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Title: Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Abstract

Downdrafts and cold pool characteristics for strong mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection are analyzed using multi-instrument data from the DOE Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign. Increases in column water vapor (CWV) are observed leading convection, with higher CWV preceding MCSs than for isolated cells. For both MCSs and isolated cells, increases in wind speed, decreases in surface moisture and temperature, and increases in relative humidity occur coincidentally with system passages. Composites of vertical velocity data and radar reflectivity from a radar wind profiler show that the downdrafts associated with the sharpest decreases in surface equivalent potential temperature (θe) have a probability of occurrence that increases with decreasing height below the freezing level. Both MCSs and unorganized convection show similar mean downdraft magnitudes and probabilities with height. Mixing computations suggest that, on average, air originating at heights greater than 3km must undergo substantial mixing, particularly in the case of isolated cells, to match the observed cold pool θe, implying a low typical origin level. Precipitation conditionally averaged on decreases in surface equivalent potential temperature (Δθe) exhibits a strong relationship because the most negative Δθe values are associated with a high probability of precipitation. The moremore » physically motivated conditional average of Δθe on precipitation shows that decreases in θe level off with increasing precipitation rate, bounded by the maximum difference between surface θe and its minimum in the profile aloft. In conclusion, robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.« less

Authors:
 [1]; ORCiD logo [1]
  1. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
Univ. of California, Los Angeles, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1502121
Grant/Contract Number:  
SC0011074
Resource Type:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 18; Journal Issue: 3; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Schiro, Kathleen A., and Neelin, J. David. Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection. United States: N. p., 2018. Web. doi:10.5194/acp-18-1997-2018.
Schiro, Kathleen A., & Neelin, J. David. Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection. United States. doi:10.5194/acp-18-1997-2018.
Schiro, Kathleen A., and Neelin, J. David. Mon . "Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection". United States. doi:10.5194/acp-18-1997-2018. https://www.osti.gov/servlets/purl/1502121.
@article{osti_1502121,
title = {Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection},
author = {Schiro, Kathleen A. and Neelin, J. David},
abstractNote = {Downdrafts and cold pool characteristics for strong mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection are analyzed using multi-instrument data from the DOE Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign. Increases in column water vapor (CWV) are observed leading convection, with higher CWV preceding MCSs than for isolated cells. For both MCSs and isolated cells, increases in wind speed, decreases in surface moisture and temperature, and increases in relative humidity occur coincidentally with system passages. Composites of vertical velocity data and radar reflectivity from a radar wind profiler show that the downdrafts associated with the sharpest decreases in surface equivalent potential temperature (θe) have a probability of occurrence that increases with decreasing height below the freezing level. Both MCSs and unorganized convection show similar mean downdraft magnitudes and probabilities with height. Mixing computations suggest that, on average, air originating at heights greater than 3km must undergo substantial mixing, particularly in the case of isolated cells, to match the observed cold pool θe, implying a low typical origin level. Precipitation conditionally averaged on decreases in surface equivalent potential temperature (Δθe) exhibits a strong relationship because the most negative Δθe values are associated with a high probability of precipitation. The more physically motivated conditional average of Δθe on precipitation shows that decreases in θe level off with increasing precipitation rate, bounded by the maximum difference between surface θe and its minimum in the profile aloft. In conclusion, robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.},
doi = {10.5194/acp-18-1997-2018},
journal = {Atmospheric Chemistry and Physics (Online)},
number = 3,
volume = 18,
place = {United States},
year = {2018},
month = {2}
}

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    Works referencing / citing this record:

    Mesoscale convective systems over the Amazon basin: The GoAmazon2014/5 program
    journal, June 2019

    • Rehbein, Amanda; Ambrizzi, Tercio; Mechoso, Carlos R.
    • International Journal of Climatology, Vol. 39, Issue 15
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    Mesoscale convective systems over the Amazon basin: The GoAmazon2014/5 program
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    • Rehbein, Amanda; Ambrizzi, Tercio; Mechoso, Carlos R.
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