University of Washington
Fields of interest
Cloud-aerosol interactions, Boundary layer, Cloud physics
Description of scientific projects
The major goal of my research is to use observational datasets in novel ways to examine the structural and behavioral properties of cloud systems and the underlying meteorology controlling them. Simple model frameworks are used to assist in the distillation of observational datasets and to develop a quantitative basis for understanding. SPECIFIC PROJECTS: 1. Synthesis of observational datasets and modeling to improve our understanding and parameterizations of boundary layer clouds over the southeast Pacific Ocean: Coupled climate models poorly simulate subtropical stratocumulus clouds, which results in climate model biases in regional top-of atmosphere radiation balance, eastern Pacific sea-surface temperature and its seasonal cycle, precipitation distribution (e.g. ‘double ITCZ’) and surface winds, and ENSO. While simulations are improving, parameterization improvement is limited in part by gaps in our understanding of key physical processes such as aerosol-cloud interactions, drizzle, entrainment, and cloud heterogeneity. Our modeling strategy and observational synthesis is designed to optimally use SEP data being currently gathered to address these gaps. The VOCALS Program and VOCALS Regional Experiment (REx) will provide important new field, extended, spaceborne, and numerical model data to better understand the coupled climate system of the SEP, and the role that the marine stratocumulus cloud systems play in this coupling. 2. Exploring the links between cloud structure and meteorology over the oceans. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and other satellites are being used to investigate cloud structural properties (cloud optical thickness and cloud top height) of cloud ensembles over the warm regions of the tropical oceans. Many questions concerning these clouds remain unanswered: what are the relative importances of the local SST and horizontal gradients of SST in determining the cloud ensemble properties in the tropics? Is the observed cancellation between shortwave and longwave cloud forcing (SWCF and LWCF) over the tropical warm pool fortuitous or the result of physical feedbacks? Over what temporal and spatial scales does this cancellation occur? How do tropical clouds respond to climate change? What are the interactions between deep convection and the structure of the tropical tropopause? How will low clouds change under a changed climate? 3. Marine Stratocumulus Cloud Systems: The marine stratocumulus cloud system is an interconnected ensemble of marine boundary layer clouds in which both radiation and precipitation work together to provide the key forcings on the marine boundary layer (MBL). Sometimes, most commonly when these systems move within roughly 500 km of coastlines, the MSCS can become perturbed by ingesting cloud condensation nuclei from continental sources. This can alter their structure and dynamics in ways that are barely understood. The hypotheses that precipitation can be an important component of the mesoscale and turbulent dynamics of these systems are supported by the few studies that have well-documented the MSCS boundary layer. My aim is to assist in the pursuit of understanding the MSCS system. The importance of the MSCS over the global oceans is rarely disputed, but remoteness is at the heart of the sampling problem. Radars need to be designed to sample these clouds, and these radars need first-class sampling platforms, on ships, on aircraft, and in space. More effort needs to be spent in learning how to better coordinate and retrieve information from our satellite missions to sample these clouds, and in devising ways to incorporate this data into our numerical models. GPS provides a wonderful, as yet largely untapped, opportunity for sampling the MBL thermodynamic structure, and should be invested in. Scatterometry is our only true spaceborne dataset to sample lower atmosphere dynamics, and should not be neglected. CloudSat and CALIPSO are providing an unprecedented dataset on the properties and organization of the precipitation and cloud structure in MSCS, and the phalanx of colocated instruments on the other A-train satellites is providing the essential context for these groundbreaking measurements.