The Effect of Moist Processes on Midlatitude Static Stability

University Of Washington, Seattle WA

Investigators

Abstract

Research conducted under this grant will study the static stability of that portion of the atmosphere (specifically the troposphere and lower stratosphere) which lies between the warm tropics and the cold polar caps (i.e. the midlatitudes). The static stability of the atmosphere is a key factor which influences many aspects of atmospheric behavior, including the frequency and intensity of convective precipitation, the propagation speed of various kinds of atmospheric wave motions, the horizontal size required for atmospheric circulation patterns to be strongly influenced by the Coriolis force, and even the strength of the atmospheric greenhouse effect. Stability is determined by the vertical variation of temperature with height, and processes which warm the upper atmosphere relative to the lower atmosphere (i.e. lessen the rate at which temperature decreases with height in the troposphere) cause an increase in static stability. The particular focus of this project is the extent to which the condensation of atmospheric water vapor and the attendant warming of the upper atmosphere by latent heating is important for determining the stability of the midlatitude atmosphere. Many previous studies have suggested that the stability of the midlatitude atmosphere is primarily determined by baroclinic instability, which can be thought of roughtly as the action of frontal systems in which warm air masses from the south are displaced by cold air masses from the north. However, some studies have shown that condensational heating could have a potentially large impact on the static stability, and it is generally accepted that condensational heating associated with convection is a primary determinant of static stability in the tropics. Research conducted under this grant will use a hierarchy of atmospheric models of varying degrees of complexity, in combination with the most recent and accurate observational datasets, to understand the fundamental physical and dynamical processes through which moisture influences midlatitude stability. The determination of midlatitude static stability is a classical problem in fundamental atmospheric science, but it also has practical real-world consequences. Previous work by the principal investigator and others shows that midlatitude stability increases with global warming, with potentially significant consequences for the hydrological cycle. In addition to the scientific broader impacts, the work would contribute to education by funding two graduate students. Scientists conducting the work will also present their research results to the public in a short video, prepared using the resources of their university.