Applications of Satellite Atmospheric Flux/Heating Data
Our group also places a strong emphasis on using the expertise we gain in developing new satellite data products to apply these datasets to study important climate problems. We are currently exploiting products from the latest satellite platforms to document the role of clouds and radiation in a changing climate and applying these benchmarks to evaluate model predictions.
Cloud Impacts on Arctic Sea Ice
Few places on Earth are experiencing changes more dramatic than those currently occurring in the Arctic. In recent years the area covered by sea ice in the Arctic during the late summer months has reduced dramatically and reached a record low in September 2007. Our group contributed to a study that showed that cloud cover was 40 % below normal over a large portion of the Arctic in the summer months preceding this record minimum. Our radiative flux calculations suggest that these clearer skies allowed significantly more sunlight to reach the surface from May through July 2007 - enough to melt a layer of sea ice 0.3 m thick or heat the ocean mixed layer by 2.4 K. Our group continues to work with climate modeling groups at the National Center for Atmospheric Research to determine how well climate models can simulate this event and to better understand the feedbacks at work in the Arctic climate system.
Role of Radiation in the Double ITCZ
It is well-known that atmospheric circulation patterns in the tropics lead to a persistent region of precipitation just north of the equator known as the Inter-Tropical Convergence Zone (ITCZ) but the lack of an equivalent precipitation band south of the equator throughout most of the year has remained a long-standing puzzle in atmospheric research. Our radiative flux datasets in combination with a heat balance model of the ocean mixed layer recently shed light on this problem showing that the seasonal emergence of a southern hemisphere ITCZ in March-April and its subsequent disappearence can be traced to a much stronger seasonal cycle in sunlight on the ocean surface south of the equator. The fact that the Earth is closer to the sun during the southern hemisphere summer months coupled with increases in reflective cloudiness during southern hemisphere winter months allows the southern hemisphere ocean to heat much more from December through February than in June, July, and August providing the necessary energy for enhanced precipitation development in March and April and subsequent cooling that shuts down this precipitation toward the end of May.
Documenting the Vertical Structure of Atmospheric Diabatic Heating and Evaluating Models
Working with colleagues on the NASA Energy and Water Cycle Study (NEWS) science team, we are also pioneering the development of the first satellite-based estimates of the vertical structure of atmospheric diabatic heating. These benchmark estimates of atmospheric heating are being compared against similar estimates from modern reanalyses like MERRA to identify potentially important biases in model physics. There is, for example, a tendency for models to over-estimate the contribution of convective precipitation to total diabatic heating. Through collaborations with modeling groups, we are conducting similar analyses to document the evolution of diabatic heating between different phases of the Madden-Julian Oscillation (MJO) with the goal of evaluating the representation of MJOs in modern reanalyses.