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Graduate Center of the City University of New York
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Papers by Matt Pfenninger
Journal of Geophysical Research, 1999
A 4-year (1993-1996) temperature and wind data set obtained from over 2000 highresolution balloon... more A 4-year (1993-1996) temperature and wind data set obtained from over 2000 highresolution balloon soundings at South Pole is used to study gravity wave characteristics in the troposphere and lower stratosphere. Extensive a, nalyses of energy density, spectra, and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at South Pole. Our results show that the gravity waves are ubiquitous and often fairly strong at South Pole, even though the generation mechanisms are not clear. Gravity wave characteristics are, in general, similar to those obtained at other high-latitude southern hemisphere stations. Potential energies vary between about 0.5 J/kg and 5 J/kg with season and altitude. Variations in kinetic energies are not well correlated with potential energy variations and range from 1 J/kg to 11 J/kg. We observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations, especially in the stratosphere. In general, the gravity waves in the stratosphere are stronger (weaker) in austral spring (fall). Wave activity in the troposphere has little seasonal dependence. Stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere. The probability of wave instability is 13.7% in the troposphere and 5.4% in the stratosphere. This is due to the less stable stratification in the troposphere, where the buoyancy period averages 8.3 rnin compared to 4.9 rnin in the stratosphere. Dynamic (shear) instability is more likely to occur than convective instability (11% versus 2.6% in the troposphere and 4.7% versus 0.7% in the stratosphere), due to the prevailing strong wind shear. The instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities (dynamic and convective instabilities combined) in both the troposphere and stratosphere.
Journal of Geophysical Research, 1999
A 4-year (1993-1996) temperature and wind data set obtained from over 2000 highresolution balloon... more A 4-year (1993-1996) temperature and wind data set obtained from over 2000 highresolution balloon soundings at South Pole is used to study gravity wave characteristics in the troposphere and lower stratosphere. Extensive a, nalyses of energy density, spectra, and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at South Pole. Our results show that the gravity waves are ubiquitous and often fairly strong at South Pole, even though the generation mechanisms are not clear. Gravity wave characteristics are, in general, similar to those obtained at other high-latitude southern hemisphere stations. Potential energies vary between about 0.5 J/kg and 5 J/kg with season and altitude. Variations in kinetic energies are not well correlated with potential energy variations and range from 1 J/kg to 11 J/kg. We observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations, especially in the stratosphere. In general, the gravity waves in the stratosphere are stronger (weaker) in austral spring (fall). Wave activity in the troposphere has little seasonal dependence. Stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere. The probability of wave instability is 13.7% in the troposphere and 5.4% in the stratosphere. This is due to the less stable stratification in the troposphere, where the buoyancy period averages 8.3 rnin compared to 4.9 rnin in the stratosphere. Dynamic (shear) instability is more likely to occur than convective instability (11% versus 2.6% in the troposphere and 4.7% versus 0.7% in the stratosphere), due to the prevailing strong wind shear. The instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities (dynamic and convective instabilities combined) in both the troposphere and stratosphere.