Recent Doctoral Defenses – Part II

Two students of David Straus defended their dissertations in Spring 2018. Both students studied intraseasonal variability in the mid-latitudes of the northern hemisphere. For some other recent defenses, see Part I.

Priyanka Yadav

Priyanka Yadav’s dissertation was on “The Character of the Mid-Latitude Response to the Fast and Slow Cycles of the Madden-Julian Oscillation Heating”.

The Madden-Julian Oscillation (MJO) is a disturbance in equatorial atmospheric convection that drifts eastward along the equator. MJO’s influence far from the equator may help forecasters better predict aspects of weather over the United States. Unlike previous work on the extratropical response to the MJO, Yadav distinguished between Fast-propagating and Slow-propagating MJO episodes.

MJO’s affect the strength of the North Atlantic Oscillation (NAO) Index (a measure of Jet Stream strength), which in turn influences northern hemisphere weather in a number of ways. One difference that Yadav found was that for the MJO Slow Modes, storm track activity strengthened before the NAO, but for FAST Modes, NAO change and storm track change occurred at the same time.

You can see Yadav’s 2017 Lightning Talk about her work. She is currently a postdoctoral researcher in the Department of Geography at the University of Delaware.

Sara Amini

Sara Amini defended a dissertation on “The impact of large-scale
circulation regimes on extreme weather over Pacific and North
America”

Atmospheric scientists have identified “circulation regimes,” which
are patterns of wind and pressure extending over regions thousands of
kilometers wide. The atmosphere has a tendency to fall into one or
another of the regimes. Numerical models show reasonable skill in
simulating these regimes, but are less successful at accurately
simulating quantities that more directly affect weather of direct
interest to society, such as precipitation or storm track
location.

Amini’s research attempted to link the circulation regimes to
storm-related quantities. Using a statistical technique (k-means
cluster analysis), she identified five regimes, including for instance
the Pacific Wavetrain and the Alaskan Ridge. She showed that geographic patterns of storm tracks and atmospheric regimes are different for different circulation regimes. Furthermore, extreme precipitation or drought are more likely to occur in different regions for different circulation regimes. These results provide a foundation for using the regimes to improve forecasts of extreme weather.