Statistical study of cloud appearance using cloud profiling radar

Seasonal and diurnal variations of cloud appearance from low to high altitude are important to study cloud formation mechanisms and their effects to the earth radiation budget. Lidar is an instrument that can measure cloud height from returned signal. However, optically thicker clouds frequently conceal existence of cloud behind them. Since millimeter-wave radio can penetrate optically thicker cloud, mm-wave cloud radars are more suitable tools for measuring cloud appearance profile.

National Institute of Information and Communications Technology (NICT) developed mm-wave (W-band) cloud radar called SPIDER in 1997. Using this radar, not only measurement on the ground but also airborne or shipboard measurements have been made for over ten years. In 2003-2006, long-term cloud observations from the ground were made at Koganei Tokyo using SPIDER. Totally over 20 months cloud profile over Tokyo were collected during this period and their variations are analyzed in this study. SPIDER can measure not only cloud echo intensity but also Doppler speed and polarization property of echoes. Using Doppler speed information, rain echo and cloud echo are classified. Insect echoes near the ground are also identified from higher LDR of radar echoes.

In this study, we found monthly averaged cloud fraction profiles shows similar profiles even in different year. It means that seasonal change of cloud profiles was obtained in this study. We also analyze data of a ceilometer next to SPIDER over 6-years duration and combined its results with SPIDER results. Diurnal variation of cloud profiles will be also discussed in this study.