Ground-based remote sensor observations during PROBE in the tropical western Pacific

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 an d 915-MHz Wind Profiler-Radio Acoustic Sounding System (RASS) observations of winds and temperatures. in addition, a dual-channel Microwave Water Subs tance Radiometer (MWSR) at 23.87 and 31.65 GHz and a Fourier Transform Infr ared Radiometer (FTIR) were operated. The FTIR operated between 500 and 200 0 cm(-1) and measured some of the first high spectral resolution (1 cm(-1)) radiation data taken in the Tropics. The microwave radiometer provided con tinuous measurements within 30-s resolution of precipitable water vapor (PW V) and integrated cloud liquid, while the RASS measured virtual temperature profiles every 30 min. In addition, occasional lidar soundings of cloud-ba se heights were available. The MWSR and FTIR data taken during PROBE were c ompared with radiosonde data. Significant differences were noted between th e MWSR and the radiosonde observations of PWV. The probability distribution of cloud liquid water was derived and is consistent with a lognormal distr ibution. During conditions that the MWSR did not indicate the presence of c loud liquid water, broadband long- and shortwave irradiance data were used to identify the presence of cirrus clouds or to confirm the presence of cle ar conditions. Comparisons are presented between measured and calculated ra diance 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 pe riod. The observations during the drying event are interpreted using PWV im ages obtained from data from the Defense Meteorological Satellite Program/S pecial Sensor Microwave/Imager and of horizontal flow measured by the wind profiler. The broadband irradiance data and the RASS soundings were also ex amined during the drying event.