INTERACTION BETWEEN STRATOSPHERIC MESOSCALE GRAVITY WAVES AND CYCLONIC ACTIVITY ON THE NORTHEASTERN AMERICAN COAST
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Authors
Geagan, Clarke
Date
2025
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Stratospheric gravity wave activity has small but distinct impacts on circulation,
thermal structure, turbulence, and mixing, rendering them crucial to accurate
understanding and modeling of the middle atmosphere. When extreme weather occurs, atmospheric disturbances can interact with the tropopause and lower stratosphere, generating and/or amplifying stratospheric mesoscale gravity wave (MGW) activity.
This study aims to identity patterns present in stratospheric MGWs during
extreme Nor’easter events, which have been identified to occur in a region that is a hotspot for gravity waves in the stratosphere, but have been minimally studied due to advances in satellite technology only allowing for effective research in the past 20-30 years, and due to gravity waves as a field being relatively niche to begin with. To accomplish the stated objective, nine case studies were selected - three comprised of major Nor’easter storms, three of moderate storms, and three of weak coastal lows.
Brightness temperature (BT) perturbations and variances were retrieved from
Atmospheric Infrared Sounder (AIRS) observations at the 4.3 !m band, which were then used to extrapolate relative comparisons between wave amplitudes Additionally, brightness temperatures associated with cloud-tops were retrieved from the 8.1 !m band, along with WPC 3-hour surface analysis data, NCEI 5-minute radar data, and SPC 12-hour 250 mb upper air maps.
These supplementary data were compared against the 4.3 !m BT perturbations
and variances for 12-hour timesteps over the course of 48 hours before and 48 hours after the selected midpoint for each of the nine events. Analysis found that results matched prior studies, and additionally identified several distinct patterns. Cases that met or exceeded the bounds for a strong event (minimum pressure < 990 mb, maximum wind >=50 kt) consistently displayed heightened wave activity (above a threshold value of variance ≥ 0.05 K2) in trough or south-of-jet regions identified in previous work as a combination of both jet and convective influences. This was also somewhat present in moderate events, but not consistently in nearly all timesteps as it was in the major Nor’easters. Along with this, results showed that tropopause overshooting, a phenomenon responsible for stratospheric MGW generation and amplification, was frequently present during strong events. When this occurred, the position of wave packets with the highest variance values either mirrored the shape of the radar mosaic where overshooting was present, or did so twelve hours later, shifted further along the storm track, but in the same shape. Finally, results showed that areas of enhanced wave activity were typically bounded by fronts, with this being nearly always the case for strong events, and with a specific tendency for variance values ≥ 0.05 to follow the shape of cold cloud-top temperatures forming the comma cloud around a center low, but only on the northwest side of associated occluded fronts.