Numerical simulations of a gravity wave event over CCOPE. Part III

The role of a mountain-plains solenoid in the generation of the second wave episode

S. E. Koch, Fuqing Zhang, M. L. Kaplan, Y. L. Lin, R. Weglarz, C. M. Trexler

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11-12 July 1981 during the Cooperative Convective Precipitation Experiment. The dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain-plains solenoid (MPS). As this updraft impinged upon a stratified shear layer above the deep, well-mixed boundary layer that developed due to strong sensible heating over the Absaroka Mountains, the gravity wave was created. This wave rapidly weakened as it propagated eastward. However, explosive convection developed directly over the remnant gravity wave as an eastward-propagating density current produced by a rainband generated within the MPS leeside convergence zone merged with a westward-propagating density current in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the movement of the incipient gravity wave as it propagated across Montana and the Dakotas. The nonlinear balance equation and Rossby number were computed to explore the role of geostrophic adjustment in the forecast gravity wave generation, as suggested in previous studies of this wave event. These fields did indicate flow imbalance, but this was merely the manifestation of the MPS-forced gravity wave. Thus, the imbalance indicator fields provided no lead time for predicting wave occurrence. Several sensitivity tests were performed to study the role of diabatic processes and topography in the initiation of the flow imbalance and the propagating gravity waves. When diabatic effects owing to precipitation were prevented, a strong gravity wave still was generated in the upper troposphere within the region of imbalance over the mountains. However, it did not have a significant impact because moist convection was necessary to maintain wave energy in the absence of an efficient wave duct. No gravity waves were present in either a simulation that disallowed surface sensible heating, or the "flat terrain" simulation, because the requisite MPS forcing could not occur. This study highlights difficulties encountered in attempting to model the generation of observed gravity waves over complex terrain in the presence of strong diabatic effects. The complex interactions that occurred between the sensible heating over complex terrain, the incipient gravity wave, and convection highlight the need for much more detailed observations between wave generation regions over mountains and the plains downstream of such regions.

Original languageEnglish (US)
Pages (from-to)909-933
Number of pages25
JournalMonthly Weather Review
Volume129
Issue number5
DOIs
StatePublished - Jan 1 2001

Fingerprint

gravity wave
mountain
simulation
convection
wave generation
complex terrain
updraft
heating
density current
plain
diabatic process
rainband
Rossby number
wave energy
mixed layer
explosive
troposphere
boundary layer
topography

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Koch, S. E. ; Zhang, Fuqing ; Kaplan, M. L. ; Lin, Y. L. ; Weglarz, R. ; Trexler, C. M. / Numerical simulations of a gravity wave event over CCOPE. Part III : The role of a mountain-plains solenoid in the generation of the second wave episode. In: Monthly Weather Review. 2001 ; Vol. 129, No. 5. pp. 909-933.
@article{01fa99299989416c848bf2ac4eee9b01,
title = "Numerical simulations of a gravity wave event over CCOPE. Part III: The role of a mountain-plains solenoid in the generation of the second wave episode",
abstract = "Mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11-12 July 1981 during the Cooperative Convective Precipitation Experiment. The dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain-plains solenoid (MPS). As this updraft impinged upon a stratified shear layer above the deep, well-mixed boundary layer that developed due to strong sensible heating over the Absaroka Mountains, the gravity wave was created. This wave rapidly weakened as it propagated eastward. However, explosive convection developed directly over the remnant gravity wave as an eastward-propagating density current produced by a rainband generated within the MPS leeside convergence zone merged with a westward-propagating density current in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the movement of the incipient gravity wave as it propagated across Montana and the Dakotas. The nonlinear balance equation and Rossby number were computed to explore the role of geostrophic adjustment in the forecast gravity wave generation, as suggested in previous studies of this wave event. These fields did indicate flow imbalance, but this was merely the manifestation of the MPS-forced gravity wave. Thus, the imbalance indicator fields provided no lead time for predicting wave occurrence. Several sensitivity tests were performed to study the role of diabatic processes and topography in the initiation of the flow imbalance and the propagating gravity waves. When diabatic effects owing to precipitation were prevented, a strong gravity wave still was generated in the upper troposphere within the region of imbalance over the mountains. However, it did not have a significant impact because moist convection was necessary to maintain wave energy in the absence of an efficient wave duct. No gravity waves were present in either a simulation that disallowed surface sensible heating, or the {"}flat terrain{"} simulation, because the requisite MPS forcing could not occur. This study highlights difficulties encountered in attempting to model the generation of observed gravity waves over complex terrain in the presence of strong diabatic effects. The complex interactions that occurred between the sensible heating over complex terrain, the incipient gravity wave, and convection highlight the need for much more detailed observations between wave generation regions over mountains and the plains downstream of such regions.",
author = "Koch, {S. E.} and Fuqing Zhang and Kaplan, {M. L.} and Lin, {Y. L.} and R. Weglarz and Trexler, {C. M.}",
year = "2001",
month = "1",
day = "1",
doi = "10.1175/1520-0493(2001)129<0909:NSOAGW>2.0.CO;2",
language = "English (US)",
volume = "129",
pages = "909--933",
journal = "Monthly Weather Review",
issn = "0027-0644",
publisher = "American Meteorological Society",
number = "5",

}

Numerical simulations of a gravity wave event over CCOPE. Part III : The role of a mountain-plains solenoid in the generation of the second wave episode. / Koch, S. E.; Zhang, Fuqing; Kaplan, M. L.; Lin, Y. L.; Weglarz, R.; Trexler, C. M.

In: Monthly Weather Review, Vol. 129, No. 5, 01.01.2001, p. 909-933.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Numerical simulations of a gravity wave event over CCOPE. Part III

T2 - The role of a mountain-plains solenoid in the generation of the second wave episode

AU - Koch, S. E.

AU - Zhang, Fuqing

AU - Kaplan, M. L.

AU - Lin, Y. L.

AU - Weglarz, R.

AU - Trexler, C. M.

PY - 2001/1/1

Y1 - 2001/1/1

N2 - Mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11-12 July 1981 during the Cooperative Convective Precipitation Experiment. The dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain-plains solenoid (MPS). As this updraft impinged upon a stratified shear layer above the deep, well-mixed boundary layer that developed due to strong sensible heating over the Absaroka Mountains, the gravity wave was created. This wave rapidly weakened as it propagated eastward. However, explosive convection developed directly over the remnant gravity wave as an eastward-propagating density current produced by a rainband generated within the MPS leeside convergence zone merged with a westward-propagating density current in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the movement of the incipient gravity wave as it propagated across Montana and the Dakotas. The nonlinear balance equation and Rossby number were computed to explore the role of geostrophic adjustment in the forecast gravity wave generation, as suggested in previous studies of this wave event. These fields did indicate flow imbalance, but this was merely the manifestation of the MPS-forced gravity wave. Thus, the imbalance indicator fields provided no lead time for predicting wave occurrence. Several sensitivity tests were performed to study the role of diabatic processes and topography in the initiation of the flow imbalance and the propagating gravity waves. When diabatic effects owing to precipitation were prevented, a strong gravity wave still was generated in the upper troposphere within the region of imbalance over the mountains. However, it did not have a significant impact because moist convection was necessary to maintain wave energy in the absence of an efficient wave duct. No gravity waves were present in either a simulation that disallowed surface sensible heating, or the "flat terrain" simulation, because the requisite MPS forcing could not occur. This study highlights difficulties encountered in attempting to model the generation of observed gravity waves over complex terrain in the presence of strong diabatic effects. The complex interactions that occurred between the sensible heating over complex terrain, the incipient gravity wave, and convection highlight the need for much more detailed observations between wave generation regions over mountains and the plains downstream of such regions.

AB - Mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11-12 July 1981 during the Cooperative Convective Precipitation Experiment. The dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain-plains solenoid (MPS). As this updraft impinged upon a stratified shear layer above the deep, well-mixed boundary layer that developed due to strong sensible heating over the Absaroka Mountains, the gravity wave was created. This wave rapidly weakened as it propagated eastward. However, explosive convection developed directly over the remnant gravity wave as an eastward-propagating density current produced by a rainband generated within the MPS leeside convergence zone merged with a westward-propagating density current in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the movement of the incipient gravity wave as it propagated across Montana and the Dakotas. The nonlinear balance equation and Rossby number were computed to explore the role of geostrophic adjustment in the forecast gravity wave generation, as suggested in previous studies of this wave event. These fields did indicate flow imbalance, but this was merely the manifestation of the MPS-forced gravity wave. Thus, the imbalance indicator fields provided no lead time for predicting wave occurrence. Several sensitivity tests were performed to study the role of diabatic processes and topography in the initiation of the flow imbalance and the propagating gravity waves. When diabatic effects owing to precipitation were prevented, a strong gravity wave still was generated in the upper troposphere within the region of imbalance over the mountains. However, it did not have a significant impact because moist convection was necessary to maintain wave energy in the absence of an efficient wave duct. No gravity waves were present in either a simulation that disallowed surface sensible heating, or the "flat terrain" simulation, because the requisite MPS forcing could not occur. This study highlights difficulties encountered in attempting to model the generation of observed gravity waves over complex terrain in the presence of strong diabatic effects. The complex interactions that occurred between the sensible heating over complex terrain, the incipient gravity wave, and convection highlight the need for much more detailed observations between wave generation regions over mountains and the plains downstream of such regions.

UR - http://www.scopus.com/inward/record.url?scp=0035334746&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0035334746&partnerID=8YFLogxK

U2 - 10.1175/1520-0493(2001)129<0909:NSOAGW>2.0.CO;2

DO - 10.1175/1520-0493(2001)129<0909:NSOAGW>2.0.CO;2

M3 - Article

VL - 129

SP - 909

EP - 933

JO - Monthly Weather Review

JF - Monthly Weather Review

SN - 0027-0644

IS - 5

ER -