Notice

6.1 Desired Weather Conditions for IOPs

It has already been specified that there will be no rain for 24 hours.

It is desired that IOPs monitor a variety of surface-flux regimes, ranging from soaked ground (evaporation and Bowen ratio high) to nearly dry ground (minimal evaporation and evapotranspiration, low Bowen ratio, and most of solar radiation going into heat). Patchiness (almost guaranteed on the drier days) is desirable but not necessary for every mission.

An ideal sequence of IOPs would follow a general soaking of the area, and follow a two-week dry-down.

Preferred wind direction for IOPs is from the south, although north is acceptable. Best wind directions are from SE (134 deg) to N (00 deg) in a clockwise direction (4 o’clock to 12 o’clock).

6.2 Intercomparison Procedures

Intercomparisons of all instrumentation is necessary to account for instrument biases (important for coordinated aircraft missions and integration of aircraft, profiler, and surface data) and instrument drift (important for isolating effects of ground wetness and greenup). Procedures for each system are disscussed below.

6.2.1. Profilers

• Every flight pattern is designed to compare with at least two or the three profilers at one or more heights.
• CLASS radiosondes will be released at each profiler site.
• Grossman has arranged with Gary Johnson of Manhattan, Kansas, to compare the winds from the Beaumont profiler to those from the 150-m tower he instrumented about 3 miles to the south.

 6.2.2. Aircraft

• Every dual-aircraft flight pattern (as opposed to sequential single-aircraft patterns) includes intercomparison enroute to the Oxford profiler west of Augusta. Comparison will be attempted in sequential flight patterns.
• Low-level flight patterns will be designed to enable comparison with as many of the surface towers as possible.
• Aircraft thermodynamic and wind data will be compared to that from the radiosondes and surface, as well as the profilers.
• Physically-Based Instrument Evaluations must also be done. These include the Kissing-Cloud Base Maneuver, which enables evaluation of dew-point depression, and Stack Patterns, which enable comparison of downwelling radiation calculated from aircraft humidities to downwelling radiation sampled at the surface.

• Can be compared to aircraft.
• Radiation measurements can be compared compared to those measured or estimated from aircraft or radiosondes.
• ‘Standards’ could be carried around and compared to surface stations during weekly visits to estimates.

• Before release, sonde will be swung in a pendulum motion to equilibrate with surface station.
• If PAM stations are compared to a standard, surface stations should be subjected to same comparison.
• CLASS surface stations will be compared to Argonne automated weather stations.
• Will be compared to profilers and aircraft.

6.2.5. Surface Temperature

Comparison among the infra-red surface temperature instruments at the ASTER base, aircraft, and as many surface stations as possible can be accomplished in two ways (listed in order of confidence):

• Roving black body. Use a common black-body calibration unit for occasional comparisons.
• Lake overflight

6.2.6. Post-Experiment Calibration

Instrumentation should be subjected to post-experiment calibration.

Intercomparison Status: A running tally of all intercomparisons will be part of the duties of the CASES Coordination Center.

6.4 Instrumentation Priorities

The priorities for CASES 97 are outlined in Section 1. From an operational standpoint, the goals in the field can be translated into four categories of observations: those needed to document budgets, diurnal cycle, mesoscale variations, and comparisons to profiler data. Documentation of the first three categories contributes to a comprehensive definition of the observational data needed for model and parameterization scheme verification.

Table 6.1 shows the data systems and instruments which are most important in reaching each of the general scientific objectives.

Table 6.1. Observing priorities with respect to the scientific objectives of CASES 97-1a. (x=major; o=minor; (-)= would not be used.

Instrument Scientific Objectives

PAM and ASTER Surface Stations

S-POL Radar

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Last Modified: 20 Aug 1997