2005 Volume 83 Issue 5 Pages 895-908
A radar remote-sensing technique of humidity profiles, which was originally developed for the middle and upper atmosphere radar (the MU radar), is applied to the lower troposphere radar (LTR) with Radio Acoustic Sounding System (RASS) operated on L-band (1357.5 MHz) in order to expand the height range into the atmospheric boundary layer. Radar volume reflectivity and turbulence energy dissipation rate are derived from LTR observations of turbulence echoes. Virtual temperature profiles are simultaneously monitored by using the RASS technique. The mixing ratio of water vapor (q) is then calculated by solving a first-order differential equation of q versus height. An observational campaign of the LTR with RASS was conducted on May 28-29, 2002 at a meteorological station in Feixi, China as a part of the Coordinated Enhanced Observing Period (CEOP) project. From the observed clear air echo intensity we successfully determined a humidity profile at the height of 0.2-2.2 km. Precipitable water vapor (PWV) derived from the propagation delay of GPS radio signals was incorporated in the estimation algorithm as a constraint of the q profiles.
A kytoon was moored at about 160 m during the radar operation, and monitored temperature, pressure and humidity, though not continuously, which are used for defining the lower boundary values in retrieving q profiles. By using the RASS temperature, and kytoon data, we could successfully estimate continuous q profiles. The radar-derived q profiles generally agreed with radiosonde data. This study successfully demonstrated a potential of the humidity estimation with the LTR in the atmospheric boundary layer. Future long-term observation is expected to investigate the precision under various meteorological conditions.
