Transcript Analysis of a Gravity Wave Traversing Oklahoma on April 26, 2011 Timothy A.

Analysis of a Gravity Wave Traversing Oklahoma
on April 26, 2011
Timothy A. Bonin and Phillip B. Chilson
Atmospheric Radar Research Center and School of Meteorology, University of Oklahoma,
Norman, OK, USA
Gravity Waves – The Basics
(from Bosart and Sanders, 1986)
• Gravity waves have a direct influence on the wind field near the surface (e.g. Brunk
1949; Ferguson, 1967)
• Often, clouds and precipitation form in regions of rising motion (pressure rise) (Uccellini,
1975) and reduction of precipitation in pressure falls (Bosart and Cussen, 1973)
• Can result in more intense convective activity/lightning (Bosart and Sanders, 1986)
• Triggering mechanisms: Geostrophic adjustment, shearing instability (Uccellini and Koch,
1987), orography, and convection
Short Overview of the SMARTSonde
• Small Multifunction Research and
Teaching Sonde
• Capable of measuring T, RH, p,
mean wind, and trace gas
concentrations (ozone)
• Use of open source autopilot
software for preconfigured flight
patterns
Flight Plan – Constant Throttle
Helical Ascent
• Used for wind best wind estimation, PBL thermodynamic profiles
Motivation - Final Flight Path on April 26
SMARTSonde seemingly
pushed downward midway
through ascent.
Why?
RUC Sounding from 19Z Over Central
Oklahoma
1.
2.
3.
4.
Thick inversion with large
N2
Conditionally unstable
layer aloft
Near-critical level aloft
High vertical wind shear
(Low Ri)
NWC Mesonet Meteogram
Meteograms from SW -> NE
Track of Gravity Wave
x – No distinguishable pressure oscillation
0.7 – Magnitude of pressure oscillation
Line – Time (LT) of pressure rise
Speed of the gravity wave
•
Winds from sodar (at NWC)
Between a trough and
crest in the wave, would
expect u and v to
increase and rising
motion
( Thanks to Charlotte
Wainwright at OU for the
sodar data)
Vertical Velocities from SMARTSonde
•
Vertical Velocities from SMARTSonde
Summary
• Gravity wave was observed traversing Oklahoma from SW -> NE
• Could be observed from satellite imagery, surface pressure field, and
winds throughout the PBL
• Wave speed close to theoretical value, but slightly larger
• Wind shift largely follows what would be expected with gravity wave
except 10 minute window where trends reverse, accompanied with
sinking motion
• Multiple wave interactions?
• Wave tilt with height?
• Gravity wave may have induced convection for a severe storm later