Synoptic regime variability at the Azores site and the corresponding variability in cloud microphysical properties

 

Authors

George Tselioudis — NASA - Goddard Institute for Space Studies
Jasmine Remillard — McGill University
Andrew Ackerman — NASA - Goddard Institute for Space Studies
Ann M. Fridlind — NASA - Goddard Institute for Space Studies
Pavlos Kollias — Stony Brook University
Edward Luke — Brookhaven National Laboratory

Category

Cloud Properties

Description

The ARM Mobile Facility (AMF) deployment site in the Azores was located at the southern tier of the North Atlantic storm alley, thus experiencing frequent transitions between midlatitude and subtropical synoptic regimes that are related to the zonal placement of the North Atlantic storm track. Given that poleward shifts in midlatitude storm tracks constitute a substantial source of cloud and rain climate feedbacks, the Azores site serves as a promising location to examine relevant cloud properties and processes at scales ranging from synoptic to microphysical and to evaluate the ability of a suite of models to simulate the primary system behaviors.

Two different methods are used here to classify the synoptic regimes affecting the Azores site during the time of the AMF deployment. The first relies on a new climatology of midlatitude storminess that, in addition to locating the storm center, delineates the area of influence of a midlatitude storm. The second applies a clustering algorithm to cloud optical thickness-cloud top pressure histograms over the global domain and derives the major weather states based on the morphology of the cloud field. The two methods are used to derive the major regimes of variability over the Azores site, both from the perspective of cloud property and atmospheric dynamics variability. The relationship between the two is examined in order to isolate dynamic influences on cloud property changes. Then, data from the AMF retrievals for the period of employment are composited over regime-representative time periods in order to map the relationships between microphysical and synoptic scale changes in cloud structure and properties. In addition, recently derived microphysical retrievals of drizzle particle size distributions are statistically compared with existing regime-representative large-eddy simulations of low-lying marine clouds. The results of the study will allow us to place the AMF retrievals in the context of the global-scale cloud variability and will make possible the use of these data for the study of cloud climate feedbacks and for statistical evaluation of global model and large-eddy simulations.