Retrievals of Vertical Air Motion from the HIAPER Cloud Radar during CSET

Abstract:

Marine boundary layer cumulus and stratocumulus clouds are significant factors in the Earth’s climate system and hence need to be accurately represented in Global Climate Model (GCM) simulations. One feature germane to these clouds, and where GCMs encounter difficulty, is the transition from stratocumulus- to cumulus-capped marine boundary layers (MBLs). This transition is climatologically important due to the large decreases in cloud cover and to the significant changes in boundary layer structure that accompany it. An important component of understanding this transition is the ability to characterize the evolution of the vertical velocity structure of the MBL.  During the Cloud System Evolution in the Trades (CSET) field program, held in July and August 2015, the NSF/NCAR Gulfstream-V High-performance Instrumented Airborne Platform for Environmental Research (GV HIAPER) aircraft made several transects from California to Hawaii to characterize the stratocumulus to Cumulus transition. The GV-HIAPER carried several remote sensing and in situ instruments for observing aerosol, cloud, precipitation, radiation and meteorological properties. Within selected air masses, flight legs were conducted above, inside, and below the cloud layers during aircraft transits from California to Hawaii. The same air masses (as determined by parcel trajectory analysis) were resampled on the return flight to California a day later. Of particular importance to studying MBL clouds are the HIAPER Cloud Radar (HCR) and the High Spectral Resolution Lidar (HSRL), which provided mapping of aerosol, cloud, and precipitation structures. From the W-band HCR, full radar Doppler spectra were calculated at 0.5 sec resolution. The 532 nm HSRL was fully calibrated and used to retrieve the aerosol extinction profiles. We have first combined the data collected by the HCR and the HSRL to create a hydrometeor mask, which will be used to characterize changes in the cloud structure. The Doppler spectrum from the ocean surface echoes, together with aircraft motion data, will be used to ameliorate the radar beam broadening due to aircraft motion. After accounting for the aircraft motion we will explore techniques to retrieve the vertical air motion and cloud microphysical variables from the radar Doppler spectrum.