Mesoscale Variability in Coastal Stratocumulus Clouds Observed During Uppef2012
Abstract
Analysis of satellite imagery shows horizontally extensive coastal stratocumulus layers with closed cell mesoscale cellular convection (MCC) near the coast transitioning to open cell MCC further offshore. The nearshore MCC region had a dominant length scale of 8.5 km. The offshore open cell region had larger length scales of 12 km to 20 km. Aircraft transects conducted through the closed cell MCC exhibited variable perturbations on two distinct length scales. Perturbations associated with MCC occurred at lengths scales identical to satellite observations. Perturbations also occurred on smaller length scales due to narrow, sub-kilometer convective downdraft events imbedded within the MCC. These events showed less spatial organization than MCC, with the distance between events ranging from .5 km to 3 km, and typical event widths of 1 km or less. Typical event perturbations include colder, dryer, downdrafts. Analysis of dynamic and thermodynamic variables has shown that typical downward velocities of .25 ms-1 exist in the middle of the cloud layer, but subsequent horizontal mixing of adjacent air reduces the magnitude of thermodynamic perturbations in the downdrafts, reduces negative buoyancy, and slows the downdraft near cloud base. These narrow downdraft events are a significant source of boundary layer vertical temperature and moisture fluxes.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2014
- Accession Number
- ADA607833
Entities
People
- Kyle B. Franklin
Organizations
- Naval Postgraduate School