Synoptic circulation and land surface influences on convection in the midwest U.S. "corn belt" during the summers of 1999 and 2000. Part I: Composite synoptic environments

Andrew M. Carleton, David L. Arnold, David J. Travis, Steve Curran, Jimmy O. Adegoke

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

In the Midwest U.S. Corn Belt, the 1999 and 2000 summer seasons (15 June-15 September) expressed contrasting spatial patterns and magnitudes of precipitation (1999: dry; 2000. normal to moist). Distinct from the numerical modeling approach often used in studies of land surface-climate interactions, a "synoptic climatological" (i.e., stratified composite) approach is applied to observation data (e.g., precipitation, radar, and atmospheric reanalyses) to determine the relative influences of "top-down" synoptic atmospheric circulation (Part I, this paper) and "bottom-up" land surface mesoscale conditions (Part II) on the predominantly convective precipitation variations. Because mesoscale modeling suggests that the free-atmosphere wind speed ("background wind") regulates the land surface-atmosphere mesoscale interaction, each day's spatial range of wind speed at 500 hPa [V(500)] over the Central Corn Belt (CCB) is classified into one of five categories ranging from "weak flow" to "jet maximum." Deep convective activity (i.e., presence/absence and morphological signature type) is determined for each afternoon and early evening period from the Next Generation Weather Radar (NEXRAD) imagery. Frequencies of the resulting background wind-convection joint occurrence types for the 1999 and 2000 summer seasons are examined in the context of the statistics determined for summers in the longer period of 1996-2001, and also compose categories for which NCEP-NCAR reanalysis (NNR) fields are averaged to yield synoptic composite environments for the two study seasons. The latter composites are compared visually with high-resolution (spatial) composites of precipitation to help identify the influence of top-down climate controls. The analysis confirms that reduced (increased) organization of radar-indicated deep convection tends to occur with weaker (stronger) background flow. The summers of 1999 and 2000 differ from one another in terms of background flow and convective activity, but more so with respect to the six-summer averages, indicating that a fuller explanation of the precipitation differences in the two summers must be sought in the analysis of additional synoptic meteorological variables. The composite synoptic conditions on convection (CV) days (no convection (NC) days) in 1999 and 2000 are generalized as follows: low pressure incoming from the west (high pressure or ridging), southerly (northerly) lower-tropospheric winds, positive (negative) anomalies of moisture in the lower troposphere, rising (sinking) air in the midtroposphere, and a location south of the upper-tropospheric jet maximum (absence of an upper-tropospheric jet or one located just south of the area). Features resembling the "northerly low-level jets" identified in previous studies for the Great Plains are present on some NC-day composites. On CV days the spatial synchronization of synoptic features implying baroclinity increases with increasing background wind speed. The CV and NC composites differ least on days of weaker flow, and there are small areas within the CCB having no obvious association between precipitation elevated amounts and synoptic circulation features favoring the upward motion of air. These spatial incongruities imply a contributory influence of "stationary" (i.e., climatic) land surface mesoscale processes in convective activity, which are examined in Part II.

Original languageEnglish (US)
Pages (from-to)3389-3415
Number of pages27
JournalJournal of Climate
Volume21
Issue number14
DOIs
StatePublished - Jul 15 2008

Fingerprint

land surface
convection
maize
summer
wind velocity
radar
NEXRAD
radar imagery
atmosphere
air
climate
atmospheric circulation
modeling
low pressure
troposphere
spatial resolution
moisture
anomaly

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

@article{a460e16e993743bdbf5fd7ada3b61951,
title = "Synoptic circulation and land surface influences on convection in the midwest U.S. {"}corn belt{"} during the summers of 1999 and 2000. Part I: Composite synoptic environments",
abstract = "In the Midwest U.S. Corn Belt, the 1999 and 2000 summer seasons (15 June-15 September) expressed contrasting spatial patterns and magnitudes of precipitation (1999: dry; 2000. normal to moist). Distinct from the numerical modeling approach often used in studies of land surface-climate interactions, a {"}synoptic climatological{"} (i.e., stratified composite) approach is applied to observation data (e.g., precipitation, radar, and atmospheric reanalyses) to determine the relative influences of {"}top-down{"} synoptic atmospheric circulation (Part I, this paper) and {"}bottom-up{"} land surface mesoscale conditions (Part II) on the predominantly convective precipitation variations. Because mesoscale modeling suggests that the free-atmosphere wind speed ({"}background wind{"}) regulates the land surface-atmosphere mesoscale interaction, each day's spatial range of wind speed at 500 hPa [V(500)] over the Central Corn Belt (CCB) is classified into one of five categories ranging from {"}weak flow{"} to {"}jet maximum.{"} Deep convective activity (i.e., presence/absence and morphological signature type) is determined for each afternoon and early evening period from the Next Generation Weather Radar (NEXRAD) imagery. Frequencies of the resulting background wind-convection joint occurrence types for the 1999 and 2000 summer seasons are examined in the context of the statistics determined for summers in the longer period of 1996-2001, and also compose categories for which NCEP-NCAR reanalysis (NNR) fields are averaged to yield synoptic composite environments for the two study seasons. The latter composites are compared visually with high-resolution (spatial) composites of precipitation to help identify the influence of top-down climate controls. The analysis confirms that reduced (increased) organization of radar-indicated deep convection tends to occur with weaker (stronger) background flow. The summers of 1999 and 2000 differ from one another in terms of background flow and convective activity, but more so with respect to the six-summer averages, indicating that a fuller explanation of the precipitation differences in the two summers must be sought in the analysis of additional synoptic meteorological variables. The composite synoptic conditions on convection (CV) days (no convection (NC) days) in 1999 and 2000 are generalized as follows: low pressure incoming from the west (high pressure or ridging), southerly (northerly) lower-tropospheric winds, positive (negative) anomalies of moisture in the lower troposphere, rising (sinking) air in the midtroposphere, and a location south of the upper-tropospheric jet maximum (absence of an upper-tropospheric jet or one located just south of the area). Features resembling the {"}northerly low-level jets{"} identified in previous studies for the Great Plains are present on some NC-day composites. On CV days the spatial synchronization of synoptic features implying baroclinity increases with increasing background wind speed. The CV and NC composites differ least on days of weaker flow, and there are small areas within the CCB having no obvious association between precipitation elevated amounts and synoptic circulation features favoring the upward motion of air. These spatial incongruities imply a contributory influence of {"}stationary{"} (i.e., climatic) land surface mesoscale processes in convective activity, which are examined in Part II.",
author = "Carleton, {Andrew M.} and Arnold, {David L.} and Travis, {David J.} and Steve Curran and Adegoke, {Jimmy O.}",
year = "2008",
month = "7",
day = "15",
doi = "10.1175/2007JCLI1578.1",
language = "English (US)",
volume = "21",
pages = "3389--3415",
journal = "Journal of Climate",
issn = "0894-8755",
publisher = "American Meteorological Society",
number = "14",

}

Synoptic circulation and land surface influences on convection in the midwest U.S. "corn belt" during the summers of 1999 and 2000. Part I : Composite synoptic environments. / Carleton, Andrew M.; Arnold, David L.; Travis, David J.; Curran, Steve; Adegoke, Jimmy O.

In: Journal of Climate, Vol. 21, No. 14, 15.07.2008, p. 3389-3415.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Synoptic circulation and land surface influences on convection in the midwest U.S. "corn belt" during the summers of 1999 and 2000. Part I

T2 - Composite synoptic environments

AU - Carleton, Andrew M.

AU - Arnold, David L.

AU - Travis, David J.

AU - Curran, Steve

AU - Adegoke, Jimmy O.

PY - 2008/7/15

Y1 - 2008/7/15

N2 - In the Midwest U.S. Corn Belt, the 1999 and 2000 summer seasons (15 June-15 September) expressed contrasting spatial patterns and magnitudes of precipitation (1999: dry; 2000. normal to moist). Distinct from the numerical modeling approach often used in studies of land surface-climate interactions, a "synoptic climatological" (i.e., stratified composite) approach is applied to observation data (e.g., precipitation, radar, and atmospheric reanalyses) to determine the relative influences of "top-down" synoptic atmospheric circulation (Part I, this paper) and "bottom-up" land surface mesoscale conditions (Part II) on the predominantly convective precipitation variations. Because mesoscale modeling suggests that the free-atmosphere wind speed ("background wind") regulates the land surface-atmosphere mesoscale interaction, each day's spatial range of wind speed at 500 hPa [V(500)] over the Central Corn Belt (CCB) is classified into one of five categories ranging from "weak flow" to "jet maximum." Deep convective activity (i.e., presence/absence and morphological signature type) is determined for each afternoon and early evening period from the Next Generation Weather Radar (NEXRAD) imagery. Frequencies of the resulting background wind-convection joint occurrence types for the 1999 and 2000 summer seasons are examined in the context of the statistics determined for summers in the longer period of 1996-2001, and also compose categories for which NCEP-NCAR reanalysis (NNR) fields are averaged to yield synoptic composite environments for the two study seasons. The latter composites are compared visually with high-resolution (spatial) composites of precipitation to help identify the influence of top-down climate controls. The analysis confirms that reduced (increased) organization of radar-indicated deep convection tends to occur with weaker (stronger) background flow. The summers of 1999 and 2000 differ from one another in terms of background flow and convective activity, but more so with respect to the six-summer averages, indicating that a fuller explanation of the precipitation differences in the two summers must be sought in the analysis of additional synoptic meteorological variables. The composite synoptic conditions on convection (CV) days (no convection (NC) days) in 1999 and 2000 are generalized as follows: low pressure incoming from the west (high pressure or ridging), southerly (northerly) lower-tropospheric winds, positive (negative) anomalies of moisture in the lower troposphere, rising (sinking) air in the midtroposphere, and a location south of the upper-tropospheric jet maximum (absence of an upper-tropospheric jet or one located just south of the area). Features resembling the "northerly low-level jets" identified in previous studies for the Great Plains are present on some NC-day composites. On CV days the spatial synchronization of synoptic features implying baroclinity increases with increasing background wind speed. The CV and NC composites differ least on days of weaker flow, and there are small areas within the CCB having no obvious association between precipitation elevated amounts and synoptic circulation features favoring the upward motion of air. These spatial incongruities imply a contributory influence of "stationary" (i.e., climatic) land surface mesoscale processes in convective activity, which are examined in Part II.

AB - In the Midwest U.S. Corn Belt, the 1999 and 2000 summer seasons (15 June-15 September) expressed contrasting spatial patterns and magnitudes of precipitation (1999: dry; 2000. normal to moist). Distinct from the numerical modeling approach often used in studies of land surface-climate interactions, a "synoptic climatological" (i.e., stratified composite) approach is applied to observation data (e.g., precipitation, radar, and atmospheric reanalyses) to determine the relative influences of "top-down" synoptic atmospheric circulation (Part I, this paper) and "bottom-up" land surface mesoscale conditions (Part II) on the predominantly convective precipitation variations. Because mesoscale modeling suggests that the free-atmosphere wind speed ("background wind") regulates the land surface-atmosphere mesoscale interaction, each day's spatial range of wind speed at 500 hPa [V(500)] over the Central Corn Belt (CCB) is classified into one of five categories ranging from "weak flow" to "jet maximum." Deep convective activity (i.e., presence/absence and morphological signature type) is determined for each afternoon and early evening period from the Next Generation Weather Radar (NEXRAD) imagery. Frequencies of the resulting background wind-convection joint occurrence types for the 1999 and 2000 summer seasons are examined in the context of the statistics determined for summers in the longer period of 1996-2001, and also compose categories for which NCEP-NCAR reanalysis (NNR) fields are averaged to yield synoptic composite environments for the two study seasons. The latter composites are compared visually with high-resolution (spatial) composites of precipitation to help identify the influence of top-down climate controls. The analysis confirms that reduced (increased) organization of radar-indicated deep convection tends to occur with weaker (stronger) background flow. The summers of 1999 and 2000 differ from one another in terms of background flow and convective activity, but more so with respect to the six-summer averages, indicating that a fuller explanation of the precipitation differences in the two summers must be sought in the analysis of additional synoptic meteorological variables. The composite synoptic conditions on convection (CV) days (no convection (NC) days) in 1999 and 2000 are generalized as follows: low pressure incoming from the west (high pressure or ridging), southerly (northerly) lower-tropospheric winds, positive (negative) anomalies of moisture in the lower troposphere, rising (sinking) air in the midtroposphere, and a location south of the upper-tropospheric jet maximum (absence of an upper-tropospheric jet or one located just south of the area). Features resembling the "northerly low-level jets" identified in previous studies for the Great Plains are present on some NC-day composites. On CV days the spatial synchronization of synoptic features implying baroclinity increases with increasing background wind speed. The CV and NC composites differ least on days of weaker flow, and there are small areas within the CCB having no obvious association between precipitation elevated amounts and synoptic circulation features favoring the upward motion of air. These spatial incongruities imply a contributory influence of "stationary" (i.e., climatic) land surface mesoscale processes in convective activity, which are examined in Part II.

UR - http://www.scopus.com/inward/record.url?scp=53649100711&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=53649100711&partnerID=8YFLogxK

U2 - 10.1175/2007JCLI1578.1

DO - 10.1175/2007JCLI1578.1

M3 - Article

AN - SCOPUS:53649100711

VL - 21

SP - 3389

EP - 3415

JO - Journal of Climate

JF - Journal of Climate

SN - 0894-8755

IS - 14

ER -