Ground-Based Remote Sensor Observations during PROBE in the Tropical Western Pacific

Abstract

From 6 January to 28 February 1993, the second phase of the Pilot Radiation Observation Experiment (PROBE) was conducted in Kavieng, Papua New Guinea. Routine data taken during PROBE included radiosondes released every 6 h and 915-MHz Wind Profiler–Radio Acoustic Sounding System (RASS) observations of winds and temperatures. In addition, a dual-channel Microwave Water Substance Radiometer (MWSR) at 23.87 and 31.65 GHz and a Fourier Transform Infrared Radiometer (FTIR) were operated. The FTIR operated between 500 and 2000 cm−1 and measured some of the first high spectral resolution (1 cm−1) radiation data taken in the Tropics. The microwave radiometer provided continuous measurements within 30-s resolution of precipitable water vapor (PWV) and integrated cloud liquid, while the RASS measured virtual temperature profiles every 30 min. In addition, occasional lidar soundings of cloud-base heights were available. The MWSR and FTIR data taken during PROBE were compared with radiosonde data. Significant differences were noted between the MWSR and the radiosonde observations of PWV. The probability distribution of cloud liquid water was derived and is consistent with a lognormal distribution. During conditions that the MWSR did not indicate the presence of cloud liquid water, broadband long- and shortwave irradiance data were used to identify the presence of cirrus clouds or to confirm the presence of clear conditions. Comparisons are presented between measured and calculated radiance during clear conditions, using radiosonde data as input to a line-by-line Radiative Transfer Model. A case study is given of a drying event in which the PWV dropped from about 5.5 cm to a low of 3.8 cm during a 24-h period. The observations during the drying event are interpreted using PWV images obtained from data from the Defense Meteorological Satellite Program/Special Sensor Microwave/Imager and of horizontal flow measured by the wind profiler. The broadband irradiance data and the RASS soundings were also examined during the drying event.