CHAPTER VI. ATMOSPHERIC PROFILES
Wilfried Brutsaert
School of Civil and Environmental Engineering
Hollister Hall, Cornell University
Ithaca, NY 14853
A. INTRODUCTION
During the period June 9 through June 18, 1992, an intensive radiosounding program was conducted to measure atmospheric profiles of the wind velocity, the temperature and the specific humidity. The launch site was located near site MS002 in the northeastern part of the catchment of the Little Washita River; this location was selected in order to ensure that the measured profiles would reflect the catchment's surface features for the prevailing southwesterly winds during this time of the year. The launch times of the rawinsondes are shown in Table VI-1.
The measurements were carried out by a team from Cornell University consisting of Wilfried Brutsaert and Nelson Dias.
B. INSTRUMENTS AND DATA
The radiosounding equipment used was manufactured by Atmospheric Instrumentation Research (AIR), Boulder, Colorado. The ground station was compact enough that it could be placed inside a 9 x 12 ft tent. The radiosonde system (AIR3A, spin type) consisted of disposable sondes with dry- and wet-bulb temperature and pressure sensors, of a receiving unit on the ground, and of an optical theodolite to track the sonde. During flight the sonde, attached to a balloon, measures the data in cycles approximately 4.8s in the following sequence: dry-bulb temperature is measured at time zero; 0.6 and 1.8s later, wet-bulb temperature and pressure are measured, respectively; then after approximately 3.0s the dry-bulb temperature measurement is made again to begin the next cycle. According to the manufacturer, the response of the pressure sensor is practically instantaneous, but the dry- and wet-bulb sensors have time constants of 3 and 12s, respectively. Because of these time constants, it is necessary to further process the data if they are to be used for analysis in the boundary layer. One possible procedure for this purpose was outlined by Sugita and Brutsaert (1990). The height, y, of the sonde can be obtained from the pressure, temperature and humidity. The horizontal distance between the sonde and the release point can be calculated from the elevation angle measured by the theodolite and from y. This, in turn, with the measured azimuth angle yields the horizontal position of the sonde. Finally, successive horizontal positions allow the calculation of average wind velocity and direction over the interval; these average values are then to be assigned to the midpoint of the interval. For 5s cycles, and with typical balloon ascent rates of around 3 to 4 m/s, the vertical resolution of the measurements was around 15 to 20 m. The sounding was generally aborted above 600 hPa (i.e., 600 mb). In the figures, some examples are shown of the data that were obtained from the rawinsonde ascents. These comprise an example of a wind speed profile, and the diurnal evolution of the temperature and humidity profiles on two separate days.
C. REFERENCES
Sugita, M. and Brutsaert, W. 1990. Wind velocity measurements in the
neutral boundary layer above hilly prairie. Jour. Geophys. Res. (Atmos.), 95(D6),
7617-7624.
| Day | Date | Time | Time | Time | Time | Time |
|---|---|---|---|---|---|---|
| 161 | 92/06/09 | 1150 | 1540 | 1800 | ||
| 162 | 92/06/10 | 0931 | 1102 | 1307 | 1530 | 1800 |
| 163 | 92/06/11 | 0929 | 1059 | 1302 | 1531 | 1800 |
| 164 | 92/06/12 | 0932 | 1059 | 1308 | 1529 | 1800 |
| 165 | 92/06/13 | 0934 | 1102 | 1302 | 1530 | 1800 |
| 166 | 92/06/14 | 0927 | 1059 | 1302 | 1531 | 1757 |
| 167 | 92/06/15 | 0931 | 1056 | 1301 | 1530 | 1800 |
| 168 | 92/06/16 | 0932 | 1100 | 1303 | 1530 | 1805 |
| 169 | 92/06/17 | 0931 | 1102 | 1300 | 1530 | 1801 |
| 170 | 92/06/18 | 0931 | 1100 | 1302 | 1532 | 1800 |