Variability and vertical structure of clouds and turbulence in the stratocumulus-capped boundary layer during VOCALS
Abstract
Vertical profiles of the marine atmospheric boundary layer (MABL) and lower troposphere are composited over 7 years of ship observations in the southeast tropical Pacific (EPIC, VOCALS) stratocumulus region. Surface meteorology, air-sea turbulent and radiative fluxes, and cloud properties were measured from ships on research cruises in 2001, 2003-2008. Rawinsondes released several times a day from ships measured vertical profiles of temperature, humidity, and winds. Two unique NOAA/ESRL instruments observed nearly continuous profiles of MABL turbulence in the VOCALS Regional Experiment of 2008. A motion-compensated vertically pointing 3.2-mm W-band radar measures reflectivity, Doppler velocity, and vertical velocity variance within clouds; and a scanning High-Resolution Doppler Lidar measures aerosol cross-section and velocity variance below clouds. A sonic anemometer on the ship measures turbulent motions in situ near the surface. Soundings and the turbulence measurements show the boundary layer was at different times well mixed throughout, intermittently coupled by shallow cumulus rising into the stratocumulus clouds, and weakly stratified and decoupled below the cloud layer. The ship sampled variability of the MABL over the diurnal cycle, (2) over longitude and (3) from synoptic and mesoscale circulations passing through the region of observation. We show diurnal composites of soundings and cloud, and turbulence, and surface flux measurements. Air-sea surface fluxes were relatively constant over the 7 years, yet clouds and the vertical structure of the MABL showed considerable variability due to synoptic-scale circulations. Of the 8 transects along 20S, the inversion tilted up toward the west in 2001, 2005, 2006, 2007, and 2008 leg 2 (5 transects) and did not have a noticeable westward tilt in 2003, 2004, and 2008 leg 1 (3 transects).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A13J0428D
- Keywords:
-
- 3307 ATMOSPHERIC PROCESSES / Boundary layer processes;
- 3310 ATMOSPHERIC PROCESSES / Clouds and cloud feedbacks;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols