ENSO-related marine cloud variation and new single column marine boundary layer cloud modeling
Low cloud and precipitation anomalies associated with tropical sea surface temperature (SST) variations or El Nino/Southern Oscillation (ENSO), fall into three groups: (1) modulation of tropical deep convection associated with anomalous Walker Circulation, (2) shifts and changes in intensity of mid-latitude storm track and upper level trough associated with anomalous Hadley Circulation and Pacific-North America (PNA) type wave propagation, (3) changes in marine boundary layer (MBL) properties.Anomalies in the extratropical North Pacific, western and eastern extratropical North Atlantic (including Mediterranean Sea), and extratropical South Atlantic regions correspond to the group (2). The most interesting of the group (2) are in the mid-latitude North Pacific during summer, western North Atlantic during winter and spring, and eastern North Atlantic during late summer and autumn. In the summer time mid-latitude North Pacific, southward shifts of "SST-MBL clouds-storm track" along a zonal band are coupled with southward shift of upper level jet. In the western North Atlantic, significant ENSO anomalies of clouds are associated with PNA type atmospheric teleconnection pattern. The ENSO anomalies in the eastern North Atlantic during late summer and autumn are associated with the seasonal juxtaposition of zonally symmetric tropical warming and atmospheric wave propagation. ENSO-related MBL cloud variations associated with the group (3) are observed in the eastern tropical Pacific Ocean during cold season (July∼November), northeastern subtropical Pacific Ocean during winter time, and Arabian Sea during summer monsoon season.An idealized single column MBL cloud model is developed to describe MBL stratiform cloud variations in group (3) above. The model does a good job of reproducing observed mean climatological and perturbation variations in the northeastern subtropical and eastern tropical and southeastern subtropical Pacific Ocean---including SST, lower tropospheric static stability and divergence related effects. Similarity between observation and simulation indicates that MBL stratiform cloud properties can be well described by parameterizing decoupling as a function only of decoupled layer thickness both in cold and warm advection regimes.
- Atmospheric sciences