The Influence of Convectively Generated Thermal Forcing on the Mesoscale Circulation around Squall Lines

Pandya, Rajul; Durran, Dale R.

doi:10.1175/1520-0469(1996)053<2924:tiocgt>2.0.co;2

Cited by 131 publications

(178 citation statements)

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“…The phase shift becomes more pronounced as the MC propagates farther to the rear. A similar phase relationship is present for disturbances behind the MC; local y f minima (dotted lines) Pandya and Alexander (1999) have noted that the lowstability layers in the upper troposphere, and the abrupt increases in stability at the tropopause trap part of the wave energy in the troposphere. Nevertheless, the phase relationships between the variables and the rearward propagation of disturbances counter to the frontward advection suggest that uppertropospheric disturbances may be identified as vertically-propagating gravity waves (cf., Fig.…”

Section: Gravity Wave Interpretationmentioning

confidence: 53%

The Role of Gravity Waves in the Meso-.BETA.-Scale Cycle of Squall-Line Type Convective Systems

Kawashima

2003

Journal of the Meteorological Society of Japan

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Observed or simulated mesoscale convective systems (MCSs) often show pulsations with time periods of a few hours. In this paper, results from a two-dimensional cloud model are used to determine the dynamical processes responsible for such self-modulating oscillations (meso-b-scale cycle, MBC) in squallline type convective systems.The simulated storms have weak cold pools and include notable pulsations with time periods of 3@4 hours. These pulsations are manifested as periodic organizations of convective-scale cells into upsheartilted meso-b-scale cells (MCs). A rearward-propagating, dissipating MC and disturbances on the downshear side have the properties of vertically propagating gravity waves, with storm-relative time periods that are about 1.5 hour less than those of the MBC. Dry model simulations driven by prescribed thermal forcings show that the waves arise in response to the reduction of latent heating in the MC in its stationary stage.The evolution of storm structure following a convective burst is related to the phasing of the uppertropospheric wave disturbances relative to the lower-tropospheric disturbances. The storm exhibits multicellular structure so long as the downward and frontward acceleration phase of gravity waves exerts suppressing effects on convections behind the gust front. As the phase propagates to the rear, it in turn enhances the convergence at the terminus of the steady lower-tropospheric front-to-rear flow, aiding the cell reinvigoration there.The time period of MBC increases as MCs tilt more horizontally in their stationary growth stage, and as the storm-relative rear-to-front upper-tropospheric wind increases. The former effect increases the intrinsic period of excited waves, and the latter increases the storm-relative period of the waves by Doppler-shifting the phase speed. These results support the argument that gravity waves generated by tilted MCs are prominent in the dynamics of MBCs.

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Section: Gravity Wave Interpretationmentioning

confidence: 53%

The Role of Gravity Waves in the Meso-.BETA.-Scale Cycle of Squall-Line Type Convective Systems

Kawashima

2003

Journal of the Meteorological Society of Japan

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“…This flow is deeper and slightly less strong further behind the front. It probably corresponds to a rear-inflow jet as described by Weisman (1992) and analysed more fully by Pandya and Durran (1996). Note that the Doppler data are only available where significant reflectivity is present.…”

Section: Observations Of a Boundary-layer Cold Pool And Associated CLmentioning

confidence: 90%

“…Furthermore, a great deal of work has focussed on propagation mechanisms involving coupling between gravity waves and convection, as summarised by Cram et al (1992), including wave-CISK (convective initiation of the second kind) theories (Raymond, 1984) and the role of upper tropospheric gravity waves in exciting the rear inflow jet (Schmidt and Cotton, 1990). Pandya and Durran (1996) show that key features of two-dimensional squall lines can be accounted for directly from the gravity-wave response to the mean heating profile, largely that arising from the leading edge convection. This includes aspects of the rear-inflow jet, though they also show that this requires the gravity-wave response to be modified by the stability profile of the cold pool.…”

Section: Introductionmentioning

confidence: 99%

The evolution of an MCS over southern England. Part 1: Observations

Clark

Browning

Morcrette

et al. 2013

Quart J Royal Meteoro Soc

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The observed MCS structure broadly followed well-established theories, including the presence of a weak rear-inflow jet. In detail, however, unsteady transitions occurred involving the formation of two distinct lines of showers ahead of the initial linear system. In each case the cold pool merged with cold downdraughts from the new showers leading to a discontinuous propagation of the system. One of these lines formed independently of the MCS, very probably on a sea-breeze convergence line. The mechanism for formation of the other is unknown, but it is possible that it was triggered by ascent associated with gravity waves generated by the MCS. The merged cold pool was deeper and colder and propagated faster than the original system, eventually forming a bow echo and arc cloud as it propagated across the English Channel. Until completion of the merger, the propagation velocity of the overall system had been controlled by a combination of the above mechanisms rather than simply by cold pool dynamics.

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“…These circulations often extend well beyond the clouds and rain of an MCS (Menard and Fritsch 1989;Pandya and Durran 1996), so what appears to be the environment in radar and satellite images may, kinematically, still be the MCS.…”

Section: A Backgroundmentioning

confidence: 99%

The Kinematics of a Midlatitude, Continental Mesoscale Convective System and Its Mesoscale Vortex

Knievel

Johnson

2002

Mon. Wea. Rev.

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The authors present a unique, scale-discriminating study of the environment-relative circulations within a mesoscale convective system (MCS) and mesoscale convective vortex (MCV). The MCS, a leading convective line and trailing stratiform region that became asymmetric, passed through the National Oceanic and Atmospheric Administration (NOAA) Profiler Network (NPN) in Kansas and Oklahoma on 1 August 1996. The MCV appeared in the MCS's stratiform region just prior to the system's mature stage and grew to a depth of over 12 km as the MCS dissipated. The MCV did not apparently survive to the next day.A spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind.A mesoscale updraft, mesoscale downdraft, and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed, so these four circulations were internal and fundamental to the MCS.The mesoscale perturbation in wind in the middle troposphere extended farther behind the MCS than ahead of it, consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of MCSs with leading convective lines and trailing stratiform regions.Deepening of the MCV appeared to be reflected in the vertical wind shear at the vortex's center: as the MCV strengthened, the mesoscale shear through its lower part decreased, perhaps as wind became more vortical at increasing altitudes. Mesoscale and synoptic vertical shears were of similar magnitude, so an average of environmental soundings outside an MCS probably does not accurately represent the shear that affects an MCV. This suggests the need to reevaluate how the kinematical settings of MCVs are diagnosed.

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The Influence of Convectively Generated Thermal Forcing on the Mesoscale Circulation around Squall Lines

Cited by 131 publications

References 0 publications

The Role of Gravity Waves in the Meso-.BETA.-Scale Cycle of Squall-Line Type Convective Systems

The Role of Gravity Waves in the Meso-.BETA.-Scale Cycle of Squall-Line Type Convective Systems

The evolution of an MCS over southern England. Part 1: Observations

The Kinematics of a Midlatitude, Continental Mesoscale Convective System and Its Mesoscale Vortex

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