Modeling and Radiosonde Data Investigations of Turbulence and Mixing in the Vicinity of the Tropopause

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The tropopause is the level of the atmosphere that can be thought of as a dividing line between the lower atmosphere (troposphere) and middle atmosphere (stratosphere). This level is relevant for several reasons, one of which is that it can be a turbulent region where aircraft fly. In this award, the research team will make use of a special set of weather balloon data and high-resolution numerical modeling to investigate turbulence in the tropopause region. Beyond aviation safety, the project is also relevant for understanding how water vapor and chemical constituents move from the troposphere to the stratosphere, which affects the global climate. A graduate student will also receive training under this award.This work is aimed at answering questions about instability and turbulence in the vicinity of the tropopause. The two major goals of the project are to determine where atmospheric turbulence maximizes in relation to tropopause height and to derive estimates of effective turbulent mixing in the vicinity of the tropopause. The main tools that will be used include the US High Vertical Resolution Radiosonde Data (HVRRD) archive from 2005-on and numerical modeling using direct numerical simulations (DNS). The specific questions to be addressed include: 1) Why have some previous investigations of atmospheric turbulence found the maximum turbulence in the free atmosphere to be below the tropopause, while others have found the maximum to be above the tropopause? 2) How does the profile of atmospheric turbulence in the vicinity of the tropopause derived from Thorpe analysis of U.S. HVRRD vary from station to station? How does it depend on the underlying topography? Is there a systematic variation with latitude? Are there seasonal and diurnal variations? Can we explain these variations by gravity wave breaking or Kelvin-Helmholtz instability and different tropopause configurations? 3) How does the average turbulent mixing in the vicinity of the tropopause compare to the “effective mixing”, taking account of the presence of observed intermittent, thin, turbulent layers?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.