Radar-observed precipitation during NAME 2004
David A. Ahijevych
National Center for Atmospheric Research
ahijevyc@ucar.edu
Co-Authors:
Richard E. Carbone, National Center for Atmospheric Research
Timothy J. Lang, Stephen W. Nesbitt, Steven A. Rutledge, Colorado State
University
This work showcases version 2 of the NAME radar network composites,
which is available for download by the larger hydrologic and climate community
at http://data.eol.ucar.edu/master_list/?project=NAME. This version features
more accurate rain rate estimates and a better interpolation scheme than version
1. The rainfall rate estimates use the lowest unblocked radar beam at each grid
point and incorporate various bias corrections. Composite fields include
reflectivity, rainfall rate, height above sea level, and satellite IR brightness
temperature, and are available every 15 minutes on 0.05 and 0.02 degree
latitude-longitude grids.
This poster will describe the primary rainfall modes observed by the radar
network during NAME from 8 July to 22 August 2004. These are featured in a
reduced-dimension framework with one principal axis parallel to the Sierra Madre
Occidental and other perpendicular. Total rainfall will also be stratified by time of
the diurnal cycle and regime type. In the usual diurnal cycle, rainfall initiates over
the higher terrain and progresses toward the coast during the evening hours. In
disturbed conditions, the convection continues well out to sea and persists until
morning. These periods are also exhibit more propagating convection, which is
shown to be correlated to periods of enhanced low-level wind shear. Contrary to
an early hypothesis, our cursory evaluation of NCAR/NCEP reanalyses shows
little correlation between the position of easterly waves and the observed radarrainfall
regime.
Potentially-predictable summertime rainfall anomalies over the
southwestern US and their relation to climate variability
Bruce T. Anderson
Many investigations of the North American monsoon system, particularly
as it impacts northwestern Mexico and the southwestern United States, have
focused upon summertime precipitation and its interannual variations. Here we
study the interannual variance of summertime precipitation at 78 stations in the
southwestern US using daily Markov Chain models and empirical intensity
distributions. Results indicate that chain-dependent stochastic models with
stationary (i.e. non-varying) frequency/intensity characteristics can explain
approximately 85% of the interannual variance in the seasonal precipitation
amount; the remaining 15% is defined as .potentially predictable. because this
variance cannot be captured by the random evolution of daily rainfall events with
climatological rainfall characteristics. On average only about 10% of the
observed years at any given station contain statistically-significant changes in the
frequency and/or intensity characteristics that generate this potentiallypredictable
variance. Additional results indicate that stations can be clustered
into 6 different regions with similar occurrences of non-stochastic, interannual
variations in seasonal-mean precipitation. Large-scale and regional climate
anomalies during years in which the various clusters experienced potentially
predictable variations in the seasonal-mean rainfall amounts are presently being
analyzed and preliminary results will be presented.
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Representation of the diurnal cycle over the North American
monsoon during the NAME 2004 field campaign
Emily J. Becker and E. Hugo Berbery
Department of Atmospheric and Oceanic Science
University of Maryland
becker@atmos.umd.edu
The structure and forcings of the diurnal cycle of warm-season
precipitation during the North American Monsoon are examined for the core
Monsoon region and for the southwestern United States, using observations and
Eta model forecasts from the North American Monsoon Experiment of 2004, and
the North American Regional Reanalysis. The dominant characteristics of each
of the two regions are analyzed separately. The diurnal cycle within the core
region occurs earlier in the day at higher topographic elevations; this shift
appears in the observations, reanalysis, and, while less pronounced, in the
model forecasts. Examination of the forcings behind this cycle, including
thermodynamic forcing in the form of convective available potential energy
(CAPE) and dynamic forcing as represented by moisture flux convergence,
suggests a greater influence on the westward shift of precipitation from
thermodynamic forcing than dynamic. The diurnal cycle in the southwestern
United States, including southern Arizona and New Mexico, shows a strong
effect due to northward moisture surges from the Gulf of California. During these
occasional surges, precipitation is increased and both dynamic and
thermodynamic forcings are stronger.
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Hydrologic variations in the Gulf of California Watershed in the
context of climate change: Investigations of the recurrence of
extraordinary events and their possible consequences
Luis Brito-Castillo
The information concerning climate change in several regions of the world
is quite large, but in Mexico the studies dealing with this kind of investigations are
scarce. The air surface temperature has been the variable that best fitted the
predictions, because of its rapid response to greenhouse effect. The studies
examining minimum air surface temperatures revealed that, in Sonora, a warm
trend is observed to the west, but cold trend to the east. These results imply the
necessity to investigate the ecological response to regional climatic perturbations
such as the extreme hydrometeorological events: heavy or scarce rainfalls, flash
floods, extremely high and low temperatures, etc. In Mexico, the lack of detailed
studies focusing on the effects and the causes of such events over the
ecosystems has motivated the preparation of this proposal; our contribution is to
try to document the regional climate change and its ecological consequences,
such as the migration or invasion of species, and extinction and/or severe
damage to their habitats. For this research, the Gulf of California watershed
(GCW) has been chosen as the zone of study, from the Sonoyta river basin in
the north to the San Pedro river basin in the south, and the Pinacate and Gran
Desierto de Altar biosphere reserve (the reserve), as a specific case study, due
to its high ecological value, where the endemic or with some degree of taxonomic
differentiation, flora and fauna, or with some category of protection, represent
one of the most important biological and taxonomic values. For methodological
reasons, the study is aim to focus from the generality (the GCW) to the specificity
(the reserve), taking up our previous investigations in the GCW where we
reported rainfall and streamflow reconstruction; the 700 mb atmospheric flow
patterns related to moisture transportation toward hydrologic basins; and the
ENSO modulation effect and the modulating influence by the tropics and
adjoining waters. Also, because it results easier to first understand the climatic
effects of global and synoptic scales and then focusing on a specific region, the
reserve, where most of the information necessary to understand the climate
changes results insufficient. This is the reason to maintain using
dendrochronological techniques to reconstruct the current available information
in the reserve, and to take field samples to understand the changes in plant
structure and/or reductions in the genetic homogeneity of the species, to support
more global analysis results. To accomplish these goals a data base of the entire
zone of study will be created, that includes climatic variables (rainfall, air surface
temperatures, streamflow), maps (vector data files) and plant species (samplings
and reference works at museums); and by searching correlative mechanisms
with different indices of climate variability which help understand the origin of the
changes. This project try to give answer to questions such as: Extreme climate
events in the zone of study are part of the natural climate variability or are a
consequence of the climate change process in the same sense as it has been
reported in other regions? Are we prepared to face the consequences of these
changes? What kind of actions will be necessary to be done to attenuate the
negative effects of these changes in protected areas, such as the reserve?.
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Impact of PACS-SONET Pibal Sounding on NAME Analyses
Paul E. Ciesielski and Richard H. Johnson
Colorado State University
Department of Atmospheric Science
Michael Douglas
National Severe Storms Laboratory
During the summer of 2004, the North American Monsoon
Experiment (NAME) established an enhanced observational network over
Mexico and the southwestern United States aimed at determining the
sources and limits of predictability of warm season precipitation
associated with the NAM. Nested within the larger NAME observational
network, were 21 pibal sounding sites from the Pan American Climate
Studies Program - Sounding Network (PACS-SONET). During the
enhanced observing period of NAME from (1 July to 15 August), nearly
1500 pibal sounding were collected from these sites. These daytime-only
wind versus height soundings were typically taken around 8 and 17 LT
with the best coverage in the lower to mid-troposphere. These pibal winds
have been quality controlled and incorporated into an objectively gridded
analyses based primarily on NAME radiosonde data.
This presentation will show intercomparisons between pibal and
GPS radiosonde winds at six sites which were approximately colocated. In
addition, we will examine the impact of incorporating these pibal
soundings on various analyses computed from the objectively gridded
datasets including the following: (1) land-sea breeze circulations over
the Gulf of California (GOC), (2) atmospheric budgets computed over the
NAME enhanced budget network, and (3) the GOC low-level jet. We hope
to demonstrate that use of these pibal data provides an improved analysis
of the complex circulation patterns within the NAME region.
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Precipitation Recycling in the North American Monsoon System
Francina Dominguez
Bosilovich, M. G., 2003: On the vertical distribution of local and remote sources
of water for precipitation. Meteor. Atmos. Phys., 80, 31.41.
Dominguez, F., P. Kumar, X. Liang, and M. Ting, 2006: Impact of atmospheric
moisture storage on precipitation recycling. J. Climate, 19, 1513.1530.
The main focus of this work is to study precipitation recycling as part of the
dynamic North American Monsoon System (NAMS), and understand how
different land and atmospheric variables within the system modulate recycling. In
order to do this, we take a set of 18 land-atmosphere variables derived from
North American Regional Recycling (NARR) data to represent the
hydroclimatology of the monsoon. One of these variables is the recycling ratio, or
ratio of recycled to total precipitation, calculated at the daily timescale using the
dynamic recycling model (Dominguez et al, 2006). Multichannel Singular
Spectrum Analysis (M-SSA) is used to extract trends in the data while at the
same time selecting only the variability common to all of the variables. The first
five M-SSA modes of average 1985-1995 daily data capture many of the
characteristics of the monsoon that have been widely discussed in the literature,
such as the abrupt increase in precipitation and precipitable water, the
temperature peak prior to the rains, the shift from westerly to easterly winds and
consequent shift in zonal moisture flux, and the increase in northerly moisture
flux confined to the Gulf of California coastal region. Furthermore, we see an
increase in evapotranspiration and recycling ratio and a decrease is sensible
heat, humidity index, and the cloud base height.
The climatological analysis of NAMS precipitation recycling reveals a
positive feedback mechanism between monsoon precipitation and subsequent
increase in precipitation of recycled origin. In agreement with previous work using
water vapor traces (Bosilovich et al., 2003), our study finds that
evapotranspiration within the NAMS region significantly contributes to monsoon
rainfall after NAMS onset. While monsoon rainfall and evapotranspiration are
predominantly located in the southwestern part of the domain, recycling is
enhanced northwest of this region, indicating a relocation of soil moisture further
inland to drier regions in the north.
Focusing our analysis on the three years with longest monsoons in the
eleven-year period, an interesting a-synchronous pattern between precipitation
and recycling ratio is revealed. The longest monsoons present a characteristic
double peak in precipitation. Intense precipitation during late June and early July
is followed by a period of dry conditions and a subsequent peak in late August
precipitation. Contrary to what one might expect, recycling peaks during the
intermediate dry period. Further inspection of other land-atmosphere variables
during a long monsoon reveals that the period of decreased precipitation is
accompanied by changes in many other land-atmospheric conditions that lead to
the recycling peak.
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Possibilities for future monitoring of the North American Monsoon
Michael Douglas
The 2004 NAME activity has provided a snapshot of part of one monsoon
season over southwestern North America. This poster discusses some of the
challenges and possibilities for monitoring the North American monsoon region of
northwestern Mexico on daily to interannual time scales with different observing
systems. To describe synoptic to interannual variations of the moisture flux over
the Gulf of California and surroundings will require a capability to obtain high
vertical and spatial resolution in the lowest few km, coupled with the ability to
resolve (or at least account for) the strong diurnal cycle, and to monitor rainfall
with some confidence. The poster presents some options for providing
acceptable vertical and horizontal resolution of the wind and moisture fields, and
also discusses a hierarchy of observations, ranging from very simple point
measurements that might provide simple .indices. of monsoon .strength., to
more comprehensive observational systems that might allow more detailed
diagnostics of the monsoon and its variability. The relative advantages and
disadvantages of some of the options will be presented.
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Field Survey of Weather Stations
Luis M. Farfan
Preliminary results from a survey of weather stations in the southern part
of the Baja California Peninsula are discussed. These stations belong to the
regional network managed by the Mexican government and provide official
weather reports to Servicio Meteorologico Nacional.
During the summer of 2006, I am visiting a set of weather stations. My
goals are to: 1) document the current status of the equipment, 2) meet the
observers and discuss concerns, 3) verify station positions and elevations, 4)
document characteristics of the surrounding terrain, and 5) select locations for
installing additional stations.
The area of study is limited to the southern peninsula (25°N), where about
50 stations are located. The area receives significant rainfall during the summer,
with maxima (300-600 mm) at the higher elevations (400-600 m).
So far, 40 stations have been visited. Most of them report extreme
temperatures and rainfall over 24-hour periods. Some problems associated with
the instrumentation, station positions, and data transfer have been identified.
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Relationships between Tropical Cyclones and Rainfall in Baja
California, Mexico
Louis M. Farfan
M.A. Cosao, and L.M. Farfan CICESE, Unidad La Paz, Mexico
mcosio@cicese.mx
The influence of tropical cyclones in rainfall patterns over the Baja
California peninsula is discussed. The impact of systems over the southern
portion of the peninsula is analyzed and the study period is limited to the summer
(July- September) 2004.
We use the best-track dataset from the U.S. National Hurricane Center to
classify, based on distance from the circulation center, systems that approached
the peninsula at several ranges. Data from the upper-air station at La Paz is used
to evaluate humidity changes during the storm approach and rain-gauge reports
from Mexican government are used to determine the spatial distribution of
precipitation. Our analysis shows that the season of 2004 resulted in below
normal precipitation, when compared with the base period 1991-2004, over the
southern peninsula while above normal conditions occurred in the central
peninsula.
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Modeling Intra-Seasonal Features of 2004 North American
Monsoon Precipitation
Xiaogang Gao
This study examines the capabilities and limitations of the MM5 regional
climate model in predicting the precipitation and circulation features that
accompanied the 2004 North American Monsoon (NAM). When the model is
reinitialized every five days to restrain the growth of modeling errors, its results
for precipitation checked at sub-seasonal timescales (not for individual rainfall
events) become comparable with ground- and satellite-based observations as
well as with the NAM.s diagnostic characteristics. The modeled monthly
precipitation illustrates the evolution patterns of monsoon rainfall, although it
underestimates the rainfall amount and coverage area in comparison with
observations. The modeled daily precipitation shows the transition from dry to
wet episodes on the monsoon onset day over the Arizona-New Mexico region,
and the multi-day heavy rainfall (> 1 mm/day) and dry periods after the onset. All
these modeling predictions agree with observed variations. The model also
accurately simulated the onset and ending dates of four major moisture surges
over the Gulf of California during the 2004 monsoon season. The model
reproduced the strong diurnal variability of NAM precipitation, but did not predict
the observed diurnal feature of the precipitation peak.s shift from the mountains
to the coast during local afternoon to late night. In general, the model is able to
reproduce the major, critical patterns and dynamic variations of NAM rainfall at
intra-seasonal timescales, but still includes errors in precipitation quantity,
pattern, and timing. The numerical study suggests that these errors are due
largely to deficiencies in the model.s cumulus convective parameterization
scheme, which is responsible for the model.s precipitation generation.
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INTERANNUAL VARIATIONS IN WARM SEASON STREAMFLOW
IN NORTHWEST MEXICO
David J. Gochis, National Center for Atmospheric Research, Boulder, CO, USA
Luis Brito-Castillo, CIBNOR, Guaymas, Sonora, Méco
W. James Shuttleworth, Dept. of Hydrology and Water Resources, U. Arizona,
Tucson, AZ, USA
Hydroclimatological analysis of the North American Monsoon region of
northwest Mexico reveals significant regions of seasonal precipitation and
streamflow coherence. In this work, inter-annual variations in regionalized
rainfall-runoff relationships are explored. Modulation of precipitation by largescale
forcing mechanisms such as tropical and North Pacific sea surface
temperatures seems to have a non-linear effect on runoff generation whose
response varies by region. Analyses reveal that the El Nino-Southern Oscillation
(ENSO) exerts a modest but statistically significant influence on NAM streamflow.
Different ENSO indices exhibit markedly different correlation structures with NAM
sub-regions. The occurrence of ENSO also has a significant impact on the
partitioning of streamflow between the summer and winter seasons. The
summer ENSO influence is explained, in part, by changes in the lower
tropospheric pressure and wind fields. These changes result in modest increases
in moisture availability (higher PW) fields during La Nina episodes vs El Nino
episodes. Based on these results, the effects of ENSO variability need to be
accounted for in applying regional downscaling techniques to parent forecast
models which have difficulty representing warm season ENSO responses.
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RECENT FINDINGS FROM THE NAME EVENT RAIN GAUGE
NETWORK (NERN)
David J. Gochis, National Center for Atmospheric Research, Boulder, CO, USA
Christopher J. Watts, U. Sonora, Hermosillo, Sonora, MX
Julio-Cesar Rodriguez, IMADES, Hermosillo, Sonora, MX
Jaime Garatuza-Payan and Iran Cardenas, ITSON, Cd. Obregon, Sonora, MX
Wei Shi, CPC/NCEP/NWS/NOAA, Camp Springs, MD, USA
The NAME Event Raingauge Network (NERN) provides event rainfall
measurements at more than 90 locations in the core North American Monsoon
region of northwest Mexico. The value of the NERN data archive continues to
grow with the acquisition of each new season of data. Recent analyses using
NERN data have focused on characterizing the variability of precipitation
intensity, frequency and total accumulations as functions of time-scale and
season. These analyses characterize a precipitation regime that shows
significant variability at between seasons and an evolution of the precipitationelevation
relationship as a function the annual cycle. The NERN has also
recently been used to assess remotely sensed estimates of precipitation
characteristics from the PERSIANN product. Combined, NERN data and
analyses are contributing to a greatly improved process understanding of
precipitation in northwest Mexico and highlight the utility of the network as a
critical component of a regional climate observing system.
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Recommendation for permanent GPS receiver network in
Northwestern Mexico
Rob Kursinski
We recommend that a permanent GPS receiver network be implemented
in Northwestern Mexico to provide a multi-functional network for atmospheric and
solid earth research as well as surveying and to provide a backbone for an
internet network in Northwestern Mexico. Such a network could be assembled
relatively inexpensively either from existing older GPS receivers or new internet
ready receivers and low cost surface meteorological packages. The internet
could likely be paid for by the community where the internet would be placed as
was accomplished in Mazatan. A quick summary of applications include
1) Atmospheric research and operational forecasting
a) Weather forecasting which will use the network to determine the upstream
moisture before it flows into the semiarid southwestern North America.
b) Hydrology which will use observations of water in the gas phase to
complement the rain gauge and radar network in the NAM area.
c) Climatic monitoring which will use a long term, precise and all-weather
hydro-meteorological record of the important and relatively remote and
certainly poorly sampled NAM area.
2) Solid earth applications for a high-rate GPS network in Mexico
a) High-precision tectonics characterized by measuring plate boundary
deformation in and around the Gulf of California (a focus site for the NSF
MARGINs program) and possible diffuse deformation within the Mexican
Basin and Range province.
b) Seismology using surface waves (e.g., Larson et al., SCIENCE, 2003) and
records of near-field displacements captured by high-rate GPS receivers.
c) a network complementing the US-based PBO facility by extending CGPS
coverage into northern Mexico, and other relatively smaller-scale CGPS
networks in southern Mexico.
3) Surveying and mapping applications such as exist in the Southwestern US in
places like Tucson and Phoenix.
4) an Internet accessible phone/satellite network as required for data access
which would provide a series of internet hubs at relatively remote locations
across Northwestern Mexico, fulfilling the internet accessibility goal defined by
the Mexican government.
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Continuing research on radar-observed precipitation systems
during NAME 2004
Timothy Lang
Timothy J. Lang, Stephen W. Nesbitt, Robert Cifelli, Steven A. Rutledge, David
Lerach, Lee Nelson, and Gustavo Pereira
Colorado State University, Fort Collins, CO
David A. Ahijevych and Richard E. Carbone
National Center for Atmospheric Research
In this poster we will update the community on the current progress of our
research on the radar-observed characteristics of precipitation systems during
NAME 2004. First, we will describe Version 2 of the NAME regional radar
composites, which include additional days and times, improved partial beam
blockage correction, improved rainfall estimates, and the addition of satellite IR
brightness temperatures to filter out sea clutter. In addition, we will describe our
plans for merging the radar and NAME raingage datasets to create new rainfall
products. Next, we will present the status of our research into the influence of
easterly waves on NAME precipitation. Finally, we will present selected case
studies of the microphysical evolution of significant storms during NAME 2004,
including the hail-producing mesoscale convective system of 5-6 August.
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Advances on the implementation of the Simple Raingauge
Network in Support for NAME
Rene Lobato
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Evolution of Upper-Level Features over NAME Domain III
July 7-13, 2004
Robert A. Maddox
Dept. of Atmospheric Science
University of Arizona
Upper-level inverted troughs and cyclones often move across the NAME
domains during the summer months. However, the role that these features play
in the evolution of convection and precipitation over the NAME region is not well
documented. Upper-level features are analyzed for a week long period during
July 2004, i.e., during the NAME observational field program. The week
examined was characterized by subtle interactions between upper-level features
east of the Sierra Madre Occidental divide, as well as with the outflow from
Tropical Storm Blas, which developed over the eastern Pacific during this period.
An upper-level cyclone formed over northeast Texas late on the 7th,
developing to the south of a large MCS. This feature subsequently moved
eastward into northern Louisiana and then looped south-southwestward into the
western Gulf of Mexico. It apparently interacted with a second upper-level
cyclone that was moving north-northwestward from the Bay of Campeche. The
cyclone moving from low-latitudes appears to have become the dominant
circulation as it turned westward and moved inland over northern Mexico.
However, the resultant large, upper-level cyclone had a complex structure, with
at least three embedded circulation centers rotating around each other. The
upper-level cyclone apparently stalled in its westward movement and decayed
when it encountered the outflow from TS Blas.
The features analyzed here, as well as TS Blas, were related to moisture
increases over northwestern Mexico and Arizona that enhanced the onset of the
monsoon over the northern third of the NAME Tier I region.
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Examples of Potential Uses of GPS Precipitable Water Data in
Monsoon Studies
Robert A. Maddox
Carlos Minjarez-Sosa, Robert A. Maddox, Rob Kursinski, and Michael Leuthold
Dept. of Atmospheric Science
University of Arizona
During the NAME field observation program in summer 2004, data from a
number of GPS precipitable water sensing systems were gathered. Some NAME
researchers may not be aware of thess data, and this poster will show several
examples of how the data can be applied in studies of the monsoon. As per:
* Time series of precipitable water at different sites can capture the time
and space aspects of the moisture increases that precede the onset of the
summer rainy period. For example, the GPS data show that the monsoon onsets
during summer 2004 and summer 2005 were quite different in character. One
year (2004) exhibited an impulsive, rapid increase in precipitable water; whereas,
2005 was characterized by a gradual increase in precipitable water during a
period of about a week.
* Time series of GPS precipitable water and winds in middle levels can be
used to examine the character of moisture flux during periods of varying degrees
of wetness. Results, shown for Tucson, are extremely variable. Wet and very wet
days occur in conjunction with middle level wind directions from all quadrants of
the compass. The lack of distinct correlations between the wind directions and
the precipitable water at Tucson may indicate that high values of precipitable
water are advected around the SW US and NW MX from a variety of differing
directions as the summer passes. Past research on the monsoon would lead one
to expect that very wet days would be found on days having middle-level winds
from southeasterly directions.
* Model runs at the Univ. of Arizona using a high-resolution version of the
WRF model have been used to show that initial condition moisture analyses can
be improved if GPS precipitable water data are included. An example showing
model forecasts with and without GPS data included will be shown.
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A column view of the diurnal cycle in models vs. NAME
observations
Brian Mapes
As a part of the NAME Climate Process Team, NAME observations and
MOLTS type model-output column datasets are examined for clues to physical
process errors and successes. Several models, both regional and global, are
being intercompared with respect to their mean diurnal cycle, at several sites and
months. The surface heat budget, boundary layer evolution, diurnal winds, and
rain are the main metrics.
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Observations and analysis of the Moisture surge of Jul 12-18 during
NAME 2004.
John Mejia
CIMMS/University of Oklahoma
And
Michael Douglas
NOAA/National Severe Storms Laboratory
This poster describes observational aspects of coastally trapped
disturbances (CTD), called in the literature as .moisture surges., that were
observed in the Gulf of California during the North American Monsoon
Experiment (NAME). In particular, the attention is paid to the case of July 13-18,
which has been categorized as a .major. moisture surge event. Observations
from meteorological surface stations, radiosondes and aircraft data provides
information of the four-dimensional structure of this specific case. Perturbations
of the surface pressure, wind, temperature and dew point are tracked to describe
the surface propagation, amplitude and phase of the surge. Both the along-shore
and cross-shore sections are presented to describe the surge structure.
Radiosonde and WP-3D aircraft data are analyzed to study the vertical structure
and evolution of this surge. Only two flights, on July 12th and 13th, were
available during this event, which provide some clues on the surge genesis and
fine moisture flux structures. The role of strong convection associated with
mesoscale convective systems, which occurred in the central and northern part
of the gulf, during the development stage of the surge until its decay stage,
complicate the analysis but seem to have an important role in its diurnal scale
variability. Different questions related to the moisture surge's propagation and the
effect of the diurnal cycle of convection and low-level jet are addressed and
discussed.
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A Simple Characterization of each day during NAME 2004 using
precipitable water and mean middle-level wind direction
Carlos M. Minjarez-Sosa
A simple caharcterization of each day during the summer of 2004 has
been done using total precipitable water (both from GPS sensors and also from
rawinsonde data). Days are classified asvery wet, wet, dry, and very dry using
precipitable water. The thresholds used are station dependent.
The moisture character of each day has been compared to the mean wind
direction in middle levels (400 to 600 mb) at 1200 UTC. For locations where GPS
data were used the 1200 UTC wind is compared to the 24-hour daily average
precipitable water. When just sounding data are available, the 1200 UTC winds
and PWAT are compared.
Initial results show that from mid-June through August that conditions are
wet to very wet at Mazatlan and wind are highly persistent with directions from
030 to 180 predominating. Whereas results at Tucson are extremely variable.
Wet and very wet days occur in conjunction with middle level winds directions in
all quadrants of the compass. Conditions over the northern third of NAME Tier 1
are far more variable than they are over southern portions of Tier I , which is to
be expected.More surprising is the lack of distinct correlation between the wind
directions and the pwat at Tucson, indicating that high values of PWAT are
advected around the SW US and NW MX from a variety of differring dircetions.
Past research on the monsoon would lead one to expect that very wet days
would be found on days having middle level winds from southeasterly directions.
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The initiation and upscale growth of convection within the
diurnal cycle along the Sierra Madre Occidental
Stephen W. Nesbitt
(snesbitt@uiuc.edu)
This study will examine modes and variability in the diurnal cycle of deep
convection tied to topography within the NAME Tier-1 domain during the 2004
EOP. Specifically, ground-based precipitation retrievals the NAME Event Rain
gauge Network (NERN) and polarimetrically- and NERN- tuned CSU/NCAR
version 2 radar composite precipitation estimates over the southern NAME Tier-I
domain will be compared with rainfall estimates from the CMORPH, TRMM
3B42, and PERSIANN to examine the timing and magnitude of the diurnal cycle
along the western slopes of the Sierra Madre Occidental (SMO). In addition,
half-hourly images of 11-micrometer brightness temperatures from GOES will be
analyzed to examine the modes of vertical development of convection as a
function of topography and the diurnal cycle. Furthermore, vertical profiles of
radar reflectivity from the TRMM precipitation radar will be examined to elucidate
convective vertical structure as a function of topography in context with the
GOES results.
Preliminary results, confirming the inference of Hong et al. (2006,
conditionally accepted in J. Hydromet.) show that over the highest terrain (above
2000 m), shallow convection tends to form just west (downwind) of the highest
terrain just before local noon, and thus warm rain microphysical processes are
important in rainfall production early in the diurnal cycle. The onset of deep
convection (defined as cloud tops which reach a cold IR brightness temperature
less than 208K) is delayed until 1500 LT, and occurs almost exclusively in terrain
below 2000 m elevation, where it continues to grow upscale and organize into
mesoscale convective systems. In this poster, we will examine the intraseasonal
variation in these processes, as well as the environments that control deep
convective growth by examining limited surface thermodynamic data available in
the high terrain of the SMO during the NAME EOP.
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Eastern Pacific tropical cyclone development and the North
American Mosoon System
Elizabeth A. Ritchie
We describe the preliminary results of an investigation of the role of
eastern Pacific tropical cyclone activity in the North American Monsoon System
(NAMS). Tropical cyclones and their remnants account for a significant fraction of
summer rainfall across parts of the NAMS domain. The goals of this project are
to (1) assess the capabilities of a high-resolution regional model (MM5) for
simulating tropical cyclones in the context of the monsoon circulation, (2) assess
the interannual variability of eastern Pacific tropical cyclones and their tracks in
the observational record, relating such variability to monsoon precipitation
indices, and (3) use the model to examine sources of potential predictability of
cyclone activity on seasonal/interannual time scales.
The initial simulations illustrate the sensitivity of model-simulated cyclone
development and both oceanic and continental precipitation to model
parameterizations of physical processes and the location of prescribed lateral
boundary conditions. There are considerable sensitivities to the physical
parameterizations used and definite biases toward producing either realistic
continental or oceanic precipitation depending on the choice of convective
parameterization. Results of these sensitivities will be shown and an initial
assessment of MM5 to accurately predict important features of the NAMS as well
as tropical cyclone activity will be discussed.
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Analysis of the 13-14 July gulf surge event during the 2004 North
American Monsoon Experiment
Peter J. Rogers Colorado State University, Fort Collins, CO; and R. H. Johnson
Gulf surges are disturbances that move northward along the Gulf of
California (GoC) frequently advecting cool, moist air from the GoC or eastern
tropical Pacific Ocean into the deserts of the southwest United States and
northwest Mexico during the North American Monsoon (NAM). High temporal
and spatial observations collected during the 2004 North American Monsoon
Experiment (NAME) are used to investigate the structure and dynamical
mechanisms of a significant gulf surge on 13 July. Integrated Sounding Systems
(ISSs) deployed along the east coast of the GoC and an enhanced network of
rawinsonde sites across the NAM region are used in this study.
Preceded by anomalous warming and a low-level nocturnal stable layer,
the surge propagates rapidly up the length of the GoC (~17-22 m s-1) and is
characterized by sharp anomalous cooling and strengthening of the wind in the
lowest 2 km of the atmosphere. The surge arrives along the northern GoC
during the early morning hours and causes a deepening of the well-mixed
boundary layer. Surface pressures rapidly rise as well. Surge characteristics are
best observed at sites along the northern GoC.
The weight of the evidence presented in this study suggests that the initial
surge over the northern gulf may be due to bore-like disturbances that owed their
existence to convective downdrafts impinging on the nocturnal inversion over the
region. Following these initial pulses, a deeper layer of sharp cooling and strong
winds ensued, which likely represents a Kelvin wave-type disturbance. Another
possibility is that the leading edge of this Kelvin wave steepened nonlinearly into
a bore-like disturbance. The data are not adequate to delineate between these
possible mechanisms.
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Sensitivity of Warm Season Precipitation and a 2004 Gulf Surge
Event to Variability in SST Forcing in the RAMS Model
Stephen Saleeby
Saleeby, S.M., and W.R. Cotton, Aug 2006.
2006 CPPA PI-Meeting and NAME SWG-8, Tucson, AZ.
The Colorado State University - Regional Atmospheric Modeling System
(CSU-RAMS) is being used to examine the variability in monsoon-related warm
season precipitation over Mexico and the United States due to variability in SST
datasets. Given recent improvements and increased resolution in satellite
derived SSTs it is pertinent to examine the sensitivity of the RAMS model to the
variety of SST data sources that are available. If model response is large due to
variations in ocean surface forcing we need to determine the most reliable
datasets for use with RAMS when trying to improve predictions and simulations
of warm season precipitation along the west coast of Mexico and the southwest
U.S. In particular, we are examining this dependence across continental scales
over the full warm season as well as across the regional scale centered around
the Gulf of California on time scales of individual surge events. As continental
and regional scale simulations become possible at higher resolution, the use of
higher resolution SSTs for surface forcing becomes a logical step in progressing
towards improving warm season precipitation predictions. Results of these
sensitivity studies will be presented and will highlight the sensitivity of the July
13-15, 2004 surge event to variable SSTs.
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The North American Regional Reanalysis estimates of the NAME
focus years.
David Salstein
The years 1990 and 2004, subjects of the NAMAP - I and NAME
campaigns were intercompared, and compared with a long climatological series,
based on the North American Regional Reanalysis (NARR) in the NAME Region
I. We note that there was a considerable difference in precipitation, water vapor
divergence, and direction of moisture transport vectors over the North American
Monsoon region in the two years. The NARR results help identify the
characteristics of seasonal variability, and they also reveal some high frequency
signals within it, including the role of the Sea of Cortez/Gulf of California in the
moisture budgets.
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NAME CPT Project - Issues for Warm Season Prediction
J. Schemm, K. Mo, L. Williams and S. Yoo , NOAA/NWS/NCEP/CPC
D. Gutzler, Univ. of New Mexico
NAME Climate Process and Modeling Team (CPT) has been established
to address the need of linking climate process research to model development
and testing activities for warm season climate prediction. The project builds on
two existing NAME-related modeling efforts. One major component of this project
is the organization and implementation of a second phase of NAMAP, based on
the 2004 season. NAMAP2 will re-examine the metrics proposed by NAMAP,
extend the NAMAP analysis to transient variability, exploit the extensive
observational database provided by NAME 2004 to analyze simulation targets of
special interest, and expand participation. Vertical column analysis will bring local
NAME observations and model outputs together in a context where key physical
processes in the models can be evaluated and improved.
The second component builds on the current NAME-related modeling
effort focused on the diurnal cycle of precipitation in several global models,
including those implemented at NCEP, NASA and GFDL. Our activities will focus
on the ability of the operational NCEP Global Forecast System (GFS) to simulate
the diurnal and seasonal evolution of warm season precipitation during the
NAME 2004 EOP, and on changes to the treatment of deep convection in the
complicated terrain of the NAMS domain that are necessary to improve the
simulations, and ultimately predictions of warm season precipitation These
activities will be strongly tied to NAMAP2 to ensure technology transfer from
research to operations.
Results based on experiments conducted with the NCEP GFS GCM will
be reported at the meeting with emphasis on the impact of horizontal resolution
in predicting warm season precipitation over North America.
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The Impact of the NAME Simple Raingauge Network
Data on the CPC Precipitation Analysis Quality
Wei Shi, R. Wayne Higgins
NOAA/Climate Prediction Center
and
Rene Lobato Sanchez
Mexican Inst. of Water Tech.
The raingauge data collected from the CPPA funded project Enhancement
of the Daily Raingauge Network in Mexico in Support of NAME has been
incorporated into CPC.s existing US_Mexico raingauge database for the period
of 2004-present. The daily precipitation analysis based on this new database is
compared to CPC.s existing real-time analyses for the same period to investigate
the impact of the new data. Intercomparisons of daily, monthly and seasonal
precipitation statistics between the analyses, and comparisons of each analysis
to a suite of satellite estimates of precipitation provide an assessment of the
range of uncertainty in our precipitation analysis products.
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Spatiotemporal Variability of Precipitation over Complex Terrain
during the North American Monsoon
Enrique R. Vivoni
Mekonnen Gebremichael and Enrique R. Vivoni
Department of Earth and Environmental Science
New Mexico Institute of Mining and Technology
Understanding the spatiotemporal distribution of precipitation is important
to produce accurate rainfall estimates for hydrometeorological applications. This
task is challenging in mountainous terrains where there are large uncertainties
associated with sparse observations and variations in the precipitation
mechanisms over short spatial and temporal scales, especially during summer
convection. The overall goal of this work is to provide a better understanding of
the local forcing mechanisms that are associated with precipitation
characteristics (spatial organization, diurnal cycle, and temporal variation). Our
analysis utilizes remote sensing and field observations collected during the North
American Monsoon Experiment-Soil Moisture Experiment (NAME-SMEX04) in
northern Sonora, Mexico. We focus on a watershed-based approach to
understanding precipitation variability. The remote sensing data include the nearsurface
rainfall rate obtained from the Precipitation Radar (PR) onboard the
TRMM satellite and the cloud infrared data onboard GOES satellites, while the
field data include rainfall observations from fifteen continuous sites. The results
of this study should shed light on orographic precipitation phenomena, on scaling
regimes in convective precipitation variability, and on the capabilities and
limitations of remote sensing observations over complex terrains during the North
American Monsoon.
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Improved Understanding of North American Monsoon
Hydrometeorology Through Integration of Field Campaigns,
Remote Sensing and Numerical Modeling
Enrique R. Vivoni and Mekonnen Gebremichael
Department of Earth and Environmental Science
New Mexico Institute of Mining and Technology
Semiarid watersheds in the southwestern United States and northwestern
Mexico have unique characteristics due to the North American Monsoon (NAM).
Nevertheless, our understanding of NAM and its links with watershed processes
is poor, in particular due to the lack of observations in northern Mexico. In this
study, we present an overview of recent research results from the Soil Moisture
Experiment 04 (SMEX04) and North American Monsoon Experiment (NAME) in
northern Sonora, Mexico. In our analysis, we utilize data sets obtained from a
network of rainfall and soil moisture sensors, remotely-sensed observations of
precipitation and soil moisture, field data sets obtained during an intensive
observation period, and geospatial data layers describing regional topography,
soils and vegetation. Furthermore, we integrate these observations into a
predictive model of the watershed hydrology in the Rio San Miguel. We focus a
portion of our analysis and modeling on reconstructing a hydrometeorological
flood event which was observed via stream gauging, in-situ sampling stations
and remote sensing. Our studies illustrate the variability of rainfall and soil
moisture, the links between the land-surface conditions and the atmospheric
state, and the utility of field and remote sensing observations for hydrological
simulations and event reconstructions.
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Impact of the Atlantic Warm Pool on the Summer Climate of the
Western Hemisphere
Chunzai Wang
The North Atlantic subtropical high (NASH), being the strongest during the
summer, determines the strength of the tropical easterly trade winds at its
southern flank. The easterly trade winds carry moisture from the tropical North
Atlantic into the Caribbean Sea where the flow intensifies forming the Caribbean
low-level jet (CLLJ). The CLLJ then splits into two branches: one turning
northward and connecting with the Great Plains low-level jet (GPLLJ), and the
other one continuing westward across Central America into the eastern North
Pacific. This paper finds that the easterly CLLJ is maximized in the summer and
winter, whereas it is minimized in the fall and spring. The semi-annual feature of
the CLLJ results from the semi-annual variation of sea level pressure in the
Caribbean region owing to the westward extensions and eastward retreats of the
NASH.
The Atlantic warm pool (AWP) with a large area of warm water is
comprised of the Gulf of Mexico, the Caribbean Sea, and the western tropical
North Atlantic. The NCAR community atmospheric model and observational data
are used to investigate the impact of the AWP on the summer climate of the
Western Hemisphere. Two groups of the model ensemble runs with and without
the AWP are performed and compared. The model results show that the AWP.s
effect is to weaken the summertime NASH, especially at its southwestern edge.
The AWP also strengthens the summertime continental low over the North
American monsoon region. In response to these pressure changes, the CLLJ is
weakened and the GPLLJ is strengthened during the summer. The weakening of
the CLLJ decreases the westward moisture transport from the AWP and thus
suppresses rainfall in the eastern North Pacific, whereas the strengthening of the
GPLLJ enhances the northward moisture transport for summer rainfall over the
central United States. Finally, the AWP largely reduces the tropospheric vertical
wind shear in the main development region that favors the hurricanes. formation
and development during August-October.
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Changes in vegetation condition and surface fluxes during NAME 2004
Chris Watts
The vegetation in the core region of the North American Monsoon (NAME)
system changes dramatically after the onset of the summer rains so that large
changes may be expected in the surface fluxes of radiation, heat and moisture.
Most of this region lies in the rugged terrain of western Mexico and very few
measurements of these fluxes have been made in the past. Surface energy
balance measurements were made at seven sites in Sonora, Mexico and
Arizona, USA during the Enhanced Observation Period (EOP) of the NAM Field
Experiment in summer 2004 to better understand how land surface vegetation
change alters energy flux partitioning. The 2004 monsoon rainfall pattern was
somewhat erratic and there was almost no rainfall in the first three weeks of
August. Satellite data was used to obtain time series for vegetation indices and
land surface temperature for these sites. The results were analyzed to contrast
conditions before the onset of the Monsoon with those afterwards. As expected,
large changes in vegetation index were observed, especially for the subtropical
sites in Sonora. However, the changes in the broadband albedo were very small,
which was rather surprising. The surface net radiation was consistent with the
previous observations, being largest for surfaces that are transpiring and cool,
and smallest for surfaces that are dry and hot. The largest evaporation rates
were observed for the subtropical and riparian vegetation. The evaporative
fraction for the forest site was highly correlated with its vegetation index, except
during the dry spell in August. This period was clearly detected in the land
surface temperature data which rose steadily in this period to a maximum at its
end.
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Influence of Sea-Surface Temperature
On the Diurnal Cycle of the North American Monsoon
System
Pingping Xie, Wanqiu Wang,
Vernon Kousky, Wei Shi, and Wayne Higgins
NOAA / NWS / Climate Prediction Center
The diurnal cycle of cloud and precipitation associated with the North
American Monsoon System (NAMS) has been examined using three-hourly data
sets of geostationary IR of Janowiak et al. 2001), the CMORPH satellite
precipitation estimates of Joyce et al. (2004), and the Multi-Platform-Merged
(MPM) SST analysis of Wang and Xie (2006) for summer 2004. A
comprehensive diagnostic study is performed to describe the temporal-spatial
structure of the mean state and diurnal cycle of the NAMS cloud/precipitation
systems and their relationship to SST over the adjacent oceanic areas. Our
results are:
1) Variations of cloudiness and precipitation associated with the
North American Monsoon System (NAMS) are dominated by
diurnal cycle;
2) Clouds and precipitation start from higher elevation in the
morning, move toward the coast as they reach the maximum in
late afternoon;
3) The phase of the diurnal cycle is relatively stable, while the
magnitude presents changes of synoptic and intraseasonal time
scales;
4) Maximum of deep convection and precipitation appears 50-
100km west to the mountain crests, and,
5) The intensity of the NAMS convection is positively (negatively)
correlated with that of the diurnal amplitude of SSTs over the
Gulf of Mexico (the Gulf of California).
Further work is underway to examine how the NAMS diurnal cycle and its
relationship to SST are simulated by NCEP operational climate forecast models.
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The role of antecedent soil moisture on variability of the North
American Monsoon System
Chenmai Zhu, Dennis P. Lettenmaier, Yun Quian, Ruby Leung
We evaluate the influence of soil moisture anomalies on the timing and
strength of North American Monsoon system (NAMS) precipitation using the
MM5 mesoscale climate model coupled with the Variable Infiltration Capacity
(VIC) land surface model. Our experiments are motivated by results of previous
data analysis that has evaluated the role of land surface conditions on variations
in monsoon precipitation in the AZ-NM and NW Mexico subregions of the NAMS
region. These previous studies showed that soil moisture memory can
propagate winter precipitation anomalies, and hence land surface cooling,
through the dry spring season and into early summer. The effect is greater in
NW Mexico where the monsoon begins earlier than in the southwestern U.S. We
further investigate this land surface feedback mechanism through a set of
coupled model runs using MM5/VIC. These coupled runs are consistent with the
previous off-line runs to the extent that the VIC land surface scheme is the basis
for soil moisture prediction in both. MM5/VIC control runs together with a set of
sensitivity experiments in which soil moisture is prescribed to field capacity,
wilting point and VIC soil moisture climatology, respectively, during pre-monsoon
seasons (April-June) are used to examine the influence of antecedent (abovenormal,
below-normal and normal) soil moisture on pre-monsoon (May and June)
surface temperature. Surface temperature, and its contrast with sea surface
temperature, is a key driver of the onset of the NAMS. These experiments are
intended to better understand the role of land-atmosphere feedbacks on the
NAMS by testing a range of land surface and climate conditions in the coupled
modeling environment.
a) Department of Civil & Environmental Engineering, University of
Washington
b) Pacific Northwest National Laboratory
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