Editorial Type:
Article
Article Type:
Research Article

Analysis of a Small, Vigorous Mesoscale Convective System in a Low-Shear Environment. Part II: Evolution of the Stratiform Precipitation and Mesoscale Flows

Kevin R. Knupp Earth System Science Laboratory, University of Alabama in Huntsville, Huntsville, Alabama

Search for other papers by Kevin R. Knupp in
Current site
Google Scholar
PubMed Close
,
Bart Geerts Earth System Science Laboratory, University of Alabama in Huntsville, Huntsville, Alabama

Search for other papers by Bart Geerts in
Current site
Google Scholar
PubMed Close
, and
John D. Tuttle National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by John D. Tuttle in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jul 1998
DOI:
https://doi.org/10.1175/1520-0493(1998)126<1837:AOASVM>2.0.CO;2
Page(s):
1837–1858
Restricted access

Abstract

The evolution of the mesoscale flow and precipitation distribution are investigated for a small mesoscale convective system (MCS) that evolved in a nearly barotropic environment exhibiting moderate instability and weak wind shear. Observations primarily from a single Doppler radar detail the growth of the MCS from the merger of several clusters and lines of vigorous convective cells into a mature state consisting of a weaker convective line trailed by an expanding stratiform precipitation region. Analysis of radar reflectivity reveals that this stratiform region formed in situ in the presence of weak mesoscale updraft as decaying convective cores coalesced, rather than through rearward advection of ice particles directly from the convective region. In the absence of sufficient low-level shear, the MCS collapsed rapidly as it assumed the structure of the archetypal convective line and trailing stratiform precipitation region.

Velocity–azimuth displays reveal mesoscale updrafts of about 70 cm s−1 during the active convective stage. In the mature stratiform region, the lower-tropospheric mesoscale downdraft (∼40 cm s−1) exceeded the mesoscale updraft (∼10 cm s−1) above it, and the level separating the two was relatively high at 6.5 km, about 2 km above the 0°C level. As the MCS cloud-top anvil area colder than −52°C peaked near 60000 km2, the cloud top descended at rates of 20–40 cm s−1 despite weak but sustained mesoscale updraft within the upper part of the cloud.

A rear inflow jet was observed before convective activity peaked, remained strong while the deep convection diminished, and became the main flow feature as the MCS decayed. This jet subsided from approximately 7 km at the rear end to near the surface at the leading edge of the convection. A weaker ascending front-to-rear current was found above this rear inflow jet.

No midlevel mesoscale cyclonic vortex was apparent in the echo structure of the maturing MCS. Indirect estimates of mesoscale vorticity, based on Lagrangian conservation of radar reflectivity, indicate that cyclonic rotation was present in the mesoscale downdraft region, and anticyclonic rotation occurred aloft. The magnitude of this vorticity is about half the Coriolis parameter. A positive potential vorticity anomaly is found at midlevels within the MCS, and this anomaly intensifies in depth and in strength as the system matures. This growth is consistent with the diabatic heating profile estimated from a 1D cloud model.

* Current affiliation: Embry-Riddle Aeronautical University, Prescott, Arizona.

Corresponding author address: Dr. Kevin R. Knupp, University of Alabama in Huntsville, Huntsville, AL 35899.

Abstract

The evolution of the mesoscale flow and precipitation distribution are investigated for a small mesoscale convective system (MCS) that evolved in a nearly barotropic environment exhibiting moderate instability and weak wind shear. Observations primarily from a single Doppler radar detail the growth of the MCS from the merger of several clusters and lines of vigorous convective cells into a mature state consisting of a weaker convective line trailed by an expanding stratiform precipitation region. Analysis of radar reflectivity reveals that this stratiform region formed in situ in the presence of weak mesoscale updraft as decaying convective cores coalesced, rather than through rearward advection of ice particles directly from the convective region. In the absence of sufficient low-level shear, the MCS collapsed rapidly as it assumed the structure of the archetypal convective line and trailing stratiform precipitation region.

Velocity–azimuth displays reveal mesoscale updrafts of about 70 cm s−1 during the active convective stage. In the mature stratiform region, the lower-tropospheric mesoscale downdraft (∼40 cm s−1) exceeded the mesoscale updraft (∼10 cm s−1) above it, and the level separating the two was relatively high at 6.5 km, about 2 km above the 0°C level. As the MCS cloud-top anvil area colder than −52°C peaked near 60000 km2, the cloud top descended at rates of 20–40 cm s−1 despite weak but sustained mesoscale updraft within the upper part of the cloud.

A rear inflow jet was observed before convective activity peaked, remained strong while the deep convection diminished, and became the main flow feature as the MCS decayed. This jet subsided from approximately 7 km at the rear end to near the surface at the leading edge of the convection. A weaker ascending front-to-rear current was found above this rear inflow jet.

No midlevel mesoscale cyclonic vortex was apparent in the echo structure of the maturing MCS. Indirect estimates of mesoscale vorticity, based on Lagrangian conservation of radar reflectivity, indicate that cyclonic rotation was present in the mesoscale downdraft region, and anticyclonic rotation occurred aloft. The magnitude of this vorticity is about half the Coriolis parameter. A positive potential vorticity anomaly is found at midlevels within the MCS, and this anomaly intensifies in depth and in strength as the system matures. This growth is consistent with the diabatic heating profile estimated from a 1D cloud model.

* Current affiliation: Embry-Riddle Aeronautical University, Prescott, Arizona.

Corresponding author address: Dr. Kevin R. Knupp, University of Alabama in Huntsville, Huntsville, AL 35899.

Save
Cover Monthly Weather Review
Monthly Weather Review

  • Biggerstaff, M. I., and R. A. Houze Jr., 1991a: Kinematic and precipitation structure of the 10–11 June 1985 squall line. Mon. Wea. Rev.,119, 3035–3065.

  • ——, and ——, 1991b: Midlevel vorticity structure of the 10–11 June 1985 squall line. Mon. Wea. Rev.,119, 3066–3079.

  • ——, and ——, 1993: Kinematics and microphysics of the transition zone of the 10–11 June 1985 squall line. J. Atmos. Sci.,50, 3091–3110.

  • Bluestein, H. B., 1993: Synoptic–Dynamic Meteorology in Midlatitudes. Volume II: Observations and Theory of Weather Systems, Oxford University Press, 594 pp.

  • Bosart, L. F., and F. Sanders, 1981: The Johnstown flood of July 1977: A long-lived convective system. J. Atmos. Sci.,38, 1616–1642.

  • Brandes, E. A., 1990: Evolution and structure of the 6–7 May 1985 mesoscale convective system and associated vortex. Mon. Wea. Rev.,118, 109–127.

  • Braun, S. A., and R. A. Houze Jr., 1995: Diagnosis of hydrometeor profiles from area-mean vertical velocity data. Quart. J. Roy. Meteor. Soc.,121, 23–53.

  • Brooks, H. E., and C. A. Doswell III, 1994: On the environments of tornadic and nontornadic mesocyclones. Wea. Forecasting,9, 606–618.

  • Browning, K. A., and R. Wexler, 1968: A determination of kinematic properties of a wind field using Doppler radar. J. Appl. Meteor.,7, 105–113.

  • Chong, M., P. Amayenc, G. Scialom, and J. Testud, 1987: A tropical squall line observed during the COPT 81 experiment in West Africa. Part I: Kinematic structure inferred from dual-Doppler radar data. Mon. Wea. Rev.,115, 670–694.

  • Fovell, R. G., and Y. Ogura, 1988: Numerical simulation of a midlatitude squall line in two dimensions. J. Atmos. Sci.,45, 3846–3879.

  • Fritsch, J. M., J. D. Murphy, and J. S. Kain, 1994: Warm core vortex amplification over land. J. Atmos. Sci.,51, 1780–1807.

  • Heymsfield, A. J., 1972: Ice crystal terminal velocities. J. Atmos. Sci.,29, 1348–1357.

  • ——, and L. J. Donner, 1990: A scheme for parameterizing ice–cloud water content in general circulation models. J. Atmos. Sci.,47, 1865–1877.

  • Hobbs, P. V., T. J. Matejka, P. H. Herzegh, J. D. Locatelli, and R. A. Houze Jr., 1980: The mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones. Part I: A case study of a cold front. J. Atmos. Sci.,37, 568–596.

  • Houze, R. A., Jr., B. F. Smull, and P. Dodge, 1990: Mesoscale organization of springtime rainstorms in Oklahoma. Mon. Wea. Rev.,118, 613–654.

  • Klimowski, B. A., 1994: Initiation and development of rear inflow within the 28–29 June 1989 North Dakota mesoconvective system. Mon. Wea. Rev.,122, 765–779.

  • Knollenberg, R. G., K. Kelly, and J. C. Wilson, 1993: Measurements of high number densities of ice crystals in the tops of tropical cumulonimbus. J. Geophys. Res.,98, 8639–8664.

  • Knupp, K. R., and V. Chandrasekar, 1993: Estimation of C-band attenuation in heavy rain environments. Preprints, 26th Int. Conf. on Radar Meteorology, Norman, OK, Amer. Meteor. Soc. 543–545.

  • ——, B. Geerts, and S. J. Goodman, 1998: Analysis of a small, vigorous mesoscale convective system. Part I: Formation, radar echo structure, and lightning behavior. Mon. Wea. Rev.,126, 1812–1836.

  • Lafore, J.-P., and M. W. Moncrieff, 1989: A numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines. J. Atmos. Sci.,46, 521–544.

  • Leise, J. A., 1981: A multi-dimensional scale-telescoped filter and data extension package. NOAA Tech Memo. WPL-82, 20 pp. [Available from NOAA/ERL/ETL, 325 Broadway, Boulder, CO 80303.].

  • Lu, Y. Y., R. J. Doviak, and C. Crisp, 1996: Estimating large scale vorticity using VAD products and reflectivity. J. Atmos. Oceanic Technol.,13, 1129–1138.

  • Raymond, D. J., and H. Jiang, 1990: A theory for long-lived mesoscale convective systems. J. Atmos. Sci.,47, 3067–3077.

  • Rinehart, R. E., 1979: Internal storm motions from a single Doppler weather radar. NCAR/TN-146+STR, 262 pp. [Available from UCAR Communications, P. O. Box 3000, Boulder, CO 80307-3000.].

  • Rotunno, R., J. B. Klemp, and M. L. Weisman, 1988: A theory for strong, long-lived squall lines. J. Atmos. Sci.,45, 463–485.

  • Rutledge, S. A., and R. A. Houze Jr., 1987: A diagnostic modeling study of the trailing stratiform region of a midlatitude squall line. J. Atmos. Sci.,44, 2640–2656.

  • ——, ——, M. I. Biggerstaff, and T. J. Matejka, 1988: The Oklahoma–Kansas mesoscale convective system of 10–11 June 1985: Precipitation structure and single Doppler radar analysis. Mon. Wea. Rev.,116, 1409–1430.

  • Sasyo, Y., 1971: Study of the formation of precipitation by the aggregation of snow particles and the accretion of cloud droplets on snow flakes. Pap. Meteor. Geophys.,22, 69–142.

  • Shapiro, A., L. Zhao, J. Zhang, J. Tuttle, S. Laroche, I. Zawadski, Q. Xu, and J. Gao, 1996: Single-Doppler velocity retrievals with hailstorm data from the North Dakota Thunderstorm Project. Preprints, 18th Conf. on Severe Local Storms, San Francisco, CA, Amer. Meteor. Soc., 546–550.

  • Skamarock, W. C., M. L. Weisman, and J. B. Klemp, 1994: Three-dimensional evolution of simulated long-lived squall lines. J. Atmos. Sci.,51, 2563–2584.

  • Smull, B. F., and R. A. Houze Jr., 1987a: Rear inflow in squall lines with trailing stratiform precipitation. Mon. Wea. Rev.,115, 2869–2889.

  • ——, and ——, 1987b: Dual-Doppler analysis of a midlatitude squall line with a trailing region of stratiform rain. J. Atmos. Sci.,44, 2128–2148.

  • Srivastava, R. C., T. J. Matejka, and T. J. Lorello, 1986: Doppler-radar study of the trailing anvil region associated with a squall line. J. Atmos. Sci.,43, 356–377.

  • Tuttle, J. D., and G. B. Foote, 1990: Determination of the boundary layer airflow from a single Doppler radar. J. Atmos. Oceanic Technol.,7, 218–232.

  • ——, and R. Gall, 1995: Radar analysis of Hurricanes Andrew and Hugo. Preprints, 21st Conf. on Hurricanes and Tropical Meteorology, Miami, FL, Amer. Meteor. Soc., 608–610.

  • Verlinde, J., and W. R. Cotton, 1990: A mesoscale vortex couplet observed in the trailing anvil of a multicellular convective complex. Mon. Wea. Rev.,118, 993–1010.

  • Weisman, M. L., 1992: The role of convectively generated rear-inflow jets in the evolution of long-lived mesoconvective systems. J. Atmos. Sci.,49, 1826–1847.

  • Willis, P. T., and A. J. Heymsfield, 1989: Structure of the melting layer in mesoscale convective system stratiform precipitation. J. Atmos. Sci.,46, 2008–2025.

  • Yeh, J. D., M. A. Fortune, and W. R. Cotton, 1986: Microphysics of the stratified precipitation region of a mesoscale convective system. Preprints, 23d Conf. on Radar Meteorology, Snowmass, CO, Amer. Meteor. Soc., 151–154.

  • Yuter, S. E., and R. A. Houze Jr., 1995: Three-dimensional kinematic and microphysical evolution of Florida cumulonimbus. Part III: Vertical mass transport, mass divergence, and synthesis. Mon. Wea. Rev.,123, 1964–1983.

  • Zhang, D. L., and K. Gao, 1989: Numerical simulation of an intense squall line during 10–11 June 1985 PRE-STORM. Part II: Rear inflow, surface pressure perturbations, and stratiform precipitation. Mon. Wea. Rev.,117, 2067–2094.

  • Ziegler, C. L., 1988: Retrieval of thermal and microphysical variables in observed convective storms. Part II: Sensitivity of cloud processes to variation of the microphysical parameterization. J. Atmos. Sci.,45, 1072–1090.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 156 67 3
PDF Downloads 116 48 4