Notice

4.1 Scope.

This chapter outlines the operations of and issues concerning radiosondes, the ABLE profiling systems, and the radar scans that will supplement the CASES-97-1 dataset.

4.2 Radiosondes

CASES-97 will use NSF/UCAR CLASS sondes, which finds winds using LORAN navigation.

4.2.1. Locations: Radiosondes will be launched from the three ABLE profiler sites whose locations and elevations are (Fig. 1.3):

• Beaumont: Elevation 478m; Latitude 37.6254N; Longitude 96.5371W (37°37'31.44"N, 96°3213'.56")
• Oxford: Elevation 360m; Latitude 37.2743N; Longitude 97.095W (37°16'27.48"N, 97°05'42"W)
• Whitewater: Elevation 425m; Latitude 37.8421N; Longitude 97.1873 W (37°50'31.56"N, 97°11'14.28"W)

IOPs: Radiosondes will be launched at 1.5-hour intervals during the five IOPs. Operators will be notified of IOPs 12 hours in advance of the IOP. This means, if an IOP starts at 0600 LDT, the operators will be notified by 1730 the previous day. For this scenario, launches will occur at the nominal times: 0600, 0730, 0900, 1030, 1200, 1330, 1500, 1630, 1800, 1930, 2100, 2230, 2400, 0130, 0300, and 0430. Note that the even-numbered hours have been set to fit with (a) the synoptic balloon-launch schedule and (b) the launch schedule followed by JETEX.

Non-IOP days: To allow sonde operators to practice and to ensure continuity, radiosondes will be released each day at two of the three sites, at the westernmost site at 1200 CDT, and at the easternmost site at 1500 CDT..

4.2.3. Coordination of Soundings with FAA

Balloon launches constitute a potential hazard for aviation. Therefore, the CASES will fax a launch schedule to the Aircraft Operations Center daily (FAX (316) 942-2101.

4.2.4. Coordination with Sonde Operators

Non-IOP Days: A schedule for balloon launches on non-IOP days has been established. Operators can contact the CASES-97 Coordination Center message phone (775-1290 or 775-2559) after 1700 CDT to hear the schedule for the next day.

IOP days Sonde operators should check ABLE Office number on non-IOP days after 1700 to see if there is an IOP the following day. The IOP will probably begin at 0600 LDT or 1800 LDT. If these notification times are changed, the operators will be notified in advance.

The day after an IOP, the predetermined schedule continues.

4.2.5. Launch Procedure

Before launch, it must be ensured that

• Thermodynamic data are stabilized. The sonde readings must be recorded along with the reading of the surface reference for later correction, if necessary.
• The sonde has `locked on' to LORAN to ensure winds to as low a level as possible

The balloon should be inflated to insure a rise rate of ~3 m/s. It should be launched away from obstacles.

Launches should be made from outside the balloon trailer. Equilibrating the sonde with environment can be achieved by gently swinging the sonde in a pendulum motion and periodically checking the temperature and humidity. Every effort should be made to make the launch as close as possible to the planned time. However, accuracy should not be sacrificed for exact simultaneity.

In the event of balloon/sonde failure, the next launch should take place as soon as possible. However, quality control efforts should not be compromised.

Time of launch, surface weather station data, and surface balloon data should be recorded for future data checking.

Balloon should be followed to the maximum altitude before time is required to prepare for the next sounding. We need data to at least 700 mb.

4.2.6. Personnel

A minimum of 2 people will be needed for each site, to work on 12-hour shifts; 3 people (8-hour shifts) are desirable. Sonde operators will be trained before the experiment.

4.2.7. Additional Data Assurance Procedures for Thermodynamics

• Calibration of surface data. The CLASS surface sensors will be calibrated before going into the field, and after returning from the field. In the field, periodic checks will be made.
• Comparing CLASS surface data to Argonne profiler surface station.
• Comparing downwelling radiation calculated from radiosonde temperature and humidity to that sampled by aircraft or surface stations.

4.2.8 Radio Frequency Interference

The following frequencies have been assigned to the three sites

OXFORD Primary 400.5

(402 S Lamont) Secondary 405.5

BEAUMONT Primary 403.5 (default)

Secondary 401.5

WHITEWATER Primary 404.5

(4010 Hillsboro) Secondary 402.0

4.3 Profilers

The three profilers are located at the vertices at the triangle that describes that CASES-97 domain (Fig. 1.3). Exact locations and altitudes are given in Section 4.2. They are operated by Argonne National

Laboratory as part of the ABLE. The Beaumont Profiler forms part of the larger ARM-CART profiler network.

4.3.1. Profiler Data

Profiler data is normally recorded in two modes: at a high vertical resolution (60-75-m) mode and a low-resolution (200-m) mode at the Whitewater and Beaumont sites. Typically, the high-resolution winds extend through the mixed layer; while the low-resolution winds extend to heights 4 km and greater.

At the Oxford profiler, which is older, is operating at a vertical resolution of 75 m all the time, with high power. The wind is estimated from an algorithm that looks for a Gaussian distribution of the signal portion of the received spectrum and ignores it if it is not so distributed. Each profiler transmits beams in 5 directions, in the following sequence: 20 deg S of zenith, 20 deg N of zenith, 20 deg E of zenith, 20 deg W of zenith and vertical, each for 30 seconds. Spectra are computed every 30 seconds. The full sequence lasts 2.5 minutes. For the Whitewater and Beaumont profilers, high-resolution (low power) and low-resolution (high power) alternate, providing a cycle time of five minutes.

At the end of 50 minutes, ‘consensus’ winds are computed in the following way. For each beam, there are 9-10 estimates. A program searches for the maximum concentration of points in a window 2 m/s wide. The median wind for these points is the consensus wind speed along the beam. These are then resolved into the u,v,w coordinates. The time assigned to the ‘consensus wind’ is the beginning time of the sequence. This method is satisfactory, assuming no signal disruptions, such as migrating birds.

RASS virtual temperatures are typically sampled he first 10 minutes after the hour. An alternative method is to sample RASS temperatures twice each hour. This provides higher resolution but the signal may be degraded.

During the IOPs for both CASES-97-1 and JETEX, the complete raw spectral data will be collected at the three profiler sites, in order to enable removal of contamination by birds in later analysis. This is a problem mainly at night, when birds migrate in large flocks. Spectral data are already routinely collected routinely at Beaumont.

4.3.2. Notification Procedure: The CASES Operators Director will notify the ABLE Operations Director (Jerry Klazura) who will notify Argonne or notify Argonne directly when an IOP is planned, so that full-spectral data can be collected at all three sites.

4.3.3. Quality Assurance: We will use comparisons of aircraft data with profiler data. Each aircraft plan has built-in flyby's of at least two of the three profilers. Radiosondes and SODAR will also be compared.

4.4. S-POL Radar

During the 5 IOPs, the S-POL will perform clear-air scans in support of CASES-1 operations.

4.4.1. Location

The S-POL radar is located 6 mi WNW of Wichita Airport (at roughly the x in Fig. 4.1, also see Fig. 1.3), at 37 deg 40' 30'' N (37.675N), 97 deg 33' 02'' W (97.551W).

4.4.2. Scans. The radar will perform two types of scans:

TREC (Tracking Reflectivity Echoes by Correlation) Boundary-Layer Scans can be used to estimate the distribution of horizontal winds. These are described in Table 4A.1

RHI (Range-Height Indicator) Scans provide a qualitative assessment of vertical boundary-layer structure. These would be done following the scan strategy given in Table 4A.2, except at horizontal intervals of 5 degrees.

4.4.3. Data Interpretation

From Figure 4.1, the west side of the CASES-97 domain is about 25 km from the radar, and the east side is roughly 100 km. A radar beam 0.5 deg above the surface would be about 150 m above the surface (Fig. 4.2) and about 400 m across (assuming 1 degree beam width) at the western edge of the watershed. At the eastern edge of the watershed, the center of the beam would be 700 m above the ground and the beam would be 1700 m wide. This estimate is complicated by the fact that the height of the surface varies across the watershed. This implies

• The horizontal variation of inversion height will be seen only in a qualitative sense, although large vertical variance in height may smear out the signal enough in the vertical to make RHIs quite informative, at least on the side of the domain near the radar.
• Interpretation of TREC winds will have to take into account the varying distance from the radar.

APPENDIX 4A: RADAR SCANNING STRATEGIES

4A.1. TREC Scans

Table 4A.1 gives the scanning strategies for the TREC mode, which consists of a series of 360-degree scans at a sequence of low elevation angles. Ideally, the radar should be in the NON-ZDR mode, but TREC scans can be made in the ZDR mode by slightly altering the scan strategy. The elevation angle spacing can be adjusted depending on the depth of the boundary layer. The highest elevation angle should penetrate the top of the boundary layer at a range of about 30-40 km. Ideally a continuous sequence of volume scans would be repeated, but if it is desired to have other scan types mixed in, then it would be best if at least three of the trek scans were repeated back-to-back following other scan types.

Table 4A.1. S-POL Radar Characteristics and boundary-layer scans

4A.2. RHI Scans

Table 4A.2 shows the scanning strategy for the RHI mode. In this scan, the antenna scans vertically at a fixed azimuth through the sequence of angles in the table, and then repeats the scans at other azimuths as prescribed (here at intervals of 5 degrees). The sector defines the fraction of area over which the RHI scans are done. The scanning strategy should optimize looking at boundary layer structure, and can be modified to achieve that end. This is based on the ‘default’ scan used by CASES-2 investigators for their RHIs, which assumes the ZDR mode. Presumably, as in the case of TREC, it would be better to use the non-ZDR mode.

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Last Modified: 20 Aug 1997