Notice

1.1. Scope and Objectives

CASES-97 is the first of several anticipated field efforts under the umbrella of the Cooperative Atmosphere Surface Exchange Study (CASES). The objective of CASES is to understand and parameterize the interactions between the earth's surface and its vegetation and the atmosphere, from turbulence time scales to years. The needed observations and their interpretation will be obtained through the cooperation of scientists from diverse fields with support and instrumentation from several organizations.

CASES-97 is a confederation of loosely coordinated complimentary experiments (Table 1.1). CASES-1 focuses on features of the fair-weather boundary and its evolution, CASES-2 focuses on radar precipitation algorithm verification and development. This document focuses on the efforts labeled CASES-97-1a and CASES-97-1b, because they require tight coordination. Coordination with CASES-2 PIs, will focus on obtaining fair-weather radar scans to supplement CASES 1a and 1b measurements. The low-level Jet Experiment (JETEX) PIs may coordinate some of their IOP's with CASES-1. Little coordination will be required with CASES-1c, whose concentrated effort will follow drydown after rainfall events, but we will consult them on soil moisture conditions. CASES-97-1c involves a post-field phase data-analysis effort.

The GEWEX Continental Scale International Project (GCIP) Enhanced Observing Period (EOP) immediately preceded the CASES -97 experiment.

We envision linkages will all these efforts as data are analyzed. In addition, comparison analyses are anticipated with the Southern Great Plains Experiment, to be conducted June 18-July 18.

The objectives of CASES 1a are:

• Relate diurnal variation of atmospheric boundary layer (ABL) profiles and depth to surface processes, the presence of clouds, and entrainment.
• Improve understanding of the diurnal forcing of the ABL profiles of wind, temperature, and humidity through evaluation of their budget equations.
• Look at the effects of surface inhomogeneities on surface fluxes, boundary layer fluxes, and boundary layer structure; test the ability of the observations to quantify the effect of inhomogeneities on ABL fluxes.
• Test ABL, surface-layer, and surface-exchange parameterization schemes in numerical models
• Optimize the design of planned long-term ABL and surface observations in the Argonne Boundary Layer Experiment (ABLE) and CASES arrays, through comparing ABLE profiles to independent observational data, and through evaluating degradation of budget calculations when CASES-97 measurements are selectively eliminated.

• Investigate mesoscale circulations driven by gradients in surface conditions and their effects on surface fluxes.
• Compare surface fluxes derived from aircraft measurement to those from other methods.
• Study entrainment processes and their dependence upon surface properties.

There is considerable overlap between the objectives of CASES-97-1a and CASE-97-1b.

1.2. Location and Duration

CASES 1a and 1b will be focused on the lower part of the Walnut River watershed located east of Wichita, Kansas (Fig. 1.1), from 22 April through 22 May 1997. Supporting Synoptic data will be collected over the central U.S. (Fig. 1.2).

1.3. Instrumentation

The objectives will be met through continuous measurements at the surface from

• Three profiling systems which provide winds from a 915-MHz Doppler-radar profiler and a SODAR. and virtual temperatures from the Radio-Acoustic Sounding System (RASS) technique. These are part of the Atmospheric Boundary Layer Experiment (ABLE) facility, operated by the Argonne National Laboratory (Fig. 1.3, Chapter 4)
• Twelve Surface flux stations (1 ABLE, 1 NOAA/ARL, 1 CU, 1 ARM/CART and 8 NSF/NCAR (Fig. 1.3, Chapter 3)),
• Daily releases of radiosondes at least once a day from two of the three profiler sites (Fig. 1.3, Chapter 3).

There will be five 24-hour Intensive Operations Periods. Decisions to have IOPs will require daily monitoring of instrumentation and weather, and a formal decision process. During IOPs,

• Radiosondes will be released at 90-minute intervals (Chapter 4).
• The NSF/Wyoming King Air and the NOAA/AOC Twin Otter will perform coordinated flight patterns (Chapter 5).
• The NSF/NCAR/S-POL radar (Fig. 1.3) will perform special scans (Chapter 6).

 Large-scale meteorological and surface context for later analysis and modeling studies will include data from satellite, the U.S. synoptic network, and model (Eta and Eta/RUC) analyses and forecasts (Table 7.1).

Table 1.1. Experiments related to CASES 97

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Last Modified: 20 Aug 1997