title climatology of high lapse rates and associated synoptic-scale flow patterns over north america...
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Title
Climatology of High Lapse Rates and Associated Synoptic-Scale Flow Patterns over
North America and the Northeast US(19742007)
Jason M. Cordeira*, Thomas J. Galarneau, Jr., and Lance F. Bosart
Dept. of Earth and Atmospheric Sciences
University at Albany/SUNY
NROW X6 November 2008
Albany, NY
Research funded by the National Science Foundation#ATM-0304254 and #ATM-0553017
MotivationMotivation -The influence of high lapse rates on severe weather
12Z 6 00Z 9 June 2007
12Z/600Z/7
00Z/7
12Z/7 00Z/8 12Z/8 00Z/9
Hail (168/8)Wind (473/5)Tornado (22)
H7-H5
Eastern extent of 700500-hPa Lapse Rate Contour (8.0 K km1)SPC event archive / RUC analyses
700500-hPa Flow
00Z/900Z/806Z/7 06Z/8
Objective
Using the North American radiosonde network:
Part I:• Establish an annual and monthly climatology of high
lapse rates over North America
Part II:• Examine seasonal and intraseasonal variability of
high lapse rates over regions of North America
Part III:• Synoptic-scale flow patterns associated with high
lapse rates over the Northeast US
Objective
Methodology (1/2)
1. Establish which stations to use in climatology:
Filters:19742007 / 12Z
(1014Z)
Accounted for “station advection”
Normalized to tmax = 12,418(34 years * 365 days + leap = 12,418)
Stations with <6,209 radiosonde observations not used (0.5 * tmax)
Methodology
118 stations
Methodology (2/2)
3. Station data:
• 700-hPa T,Z• 500-hPa T,Z
4. Calculated:• Lapse Rate ()
– Threshold of 8.0 K km1
• Potential Temperature
2. Data acquisition: [NCDC]Integrated Global Radiosonde Archive (IGRA)ftp://ftp.ncdc.noaa.gov/pub/data/igra/data-por/
Methodology
72429 90-08-28
72518 00-06-10
Part I: Results - cumulative frequency distribution
19742007
Maxima centered on:
• Elevated terrain
• Warm-season phenomenon
• Gulf of Alaska
• Cold-season phenomenon
Variability:
• How do these maxima evolve with time?
• What are the physical processes associated with each?
Shading represents 0.5 Barnes analysis of the station data
Annual
5070days/yr 13
days/yr
1525days/yr
Part I: Results - monthly frequency distributions
January19742007
Jan
Jan
Apr
Jul
Oct
5
April19742007
AprPart I: Results - monthly frequency distributions
Jan
Apr
Jul
Oct
10
July19742007
JulyPart I: Results - monthly frequency distributions
Jan
Apr
Jul
Oct
1
October19742007
OctPart I: Results - monthly frequency distributions
Jan
Apr
Jul
Oct
1
Part I: Summary - annual and monthly distributions
Month Sum
1. Cold-season maximum over Gulf of Alaska
2. Spring-time maximum over Mexico and southern Texas– Translated northwest over the Intermountain West from
MayJune
3. Expansion of Intermountain maximum toward the California coast and Northern Plains JulyAugust
Part II:• Examine seasonal and intraseasonal variability of
high lapse rates over regions of North America
Part II: Results - regional histograms
South Central Plains (SCP)
SCP
South Central PlainsRegional Monthly Frequency
Reg
iona
l Fre
quen
cy
Month
SCP
IMWPart II: Results - regional histograms
Intermountain West (IMW)
Intermountain WestRegional Monthly Frequency
Reg
iona
l Fre
quen
cy
MonthNote: y-axis scale has changed!
NWPart II: Results - regional histograms
Northwest (NW)
IMW
Similar for Upper-Midwest
NorthwestRegional Monthly Frequency
Reg
iona
l Fre
quen
cy
MonthNote: y-axis scale has changed!
CWPart II: Results - regional histograms
Canada West (CW)
NW
Canada WestRegional Monthly Frequency
Reg
iona
l Fre
quen
cy
MonthNote: y-axis scale has changed!
NEPart II: Results - regional histograms
Northeast (NE)
NortheastRegional Monthly Frequency
Reg
iona
l Fre
quen
cy
MonthNote: y-axis scale has changed!
CW
SSV NPart II: Results - sub-seasonal variability
1995700500-hPa Lapse Rate Hovmöller• ‘Transitory’
• Cold season
• Synoptic-scale periodicity
2.5 ECMWF Reanalysis
5565NHovmöller Band
5 latitude of seasonal maximum
1 Jan
1 Mar
1 May
1 Jul
1 Sep
1 Nov
1 Jan180 165W 150W 135W 120W 105W 90W
9.00 8.50 8.00 7.50 7.00
K km1
SSV SPart II: Results - sub-seasonal variability
1995700500-hPa Lapse Rate Hovmöller• ‘Transitory’
– Cold season– Synoptic-scale periodicity
• ‘Stationary’– Warm season– Synoptic-Planetary-scale periodicity
5 latitude of seasonal maximum
1 Jan
1 Mar
1 May
1 Jul
1 Sep
1 Nov
1 Jan120W 105W 90W 75W 60W 45W 30W
9.00 8.50 8.00 7.50 7.00
K km12.5 ECMWF Reanalysis
3545NHovmöller Band
~Albany
Part II: Results - mean potential temperature
N=52,402
700-500-hPa -mean bin [C]
Pot_dist
0
1
2
3
4
5
6
Bin
Frequency
Part II: Results - mean potential temperature
N=42
700-500-hPa -mean bin [C]
Pot_dist
Albany(year)
AlbanyAMJJAS
AlbanyONDJFM
1
Albany
Part II: Results - potential temperature stratification
€
> 30oC
Pot strat
Cold-season phenomenon
Characteristics:Lower tropospheric warm advectionMoist troposphereLow tropopause (~500 hPa)
Likely dynamically-driven associated with cold upper-level troughs
Intraseasonal movement related to fluctuations in the time-mean storm track
28
Part II: Results - ‘cold season’ flow pattern composite
Cold_strat
72 h 48 h
24 h 0 h
K/km
500-hPa Height / Wind and 700-500-hPa Lapse Anomaly
N=28
Part II: Results - potential temperature stratification
€
< 30oC
Pot strat
Warm-season phenomenon
Characteristics:Originated as surface-based mixed layers over elevated terrainHigh tropopause (~200 hPa)
Likely associated with strong surface sensible heating over elevated terrain
Intraseasonal movement related to synoptic-scale activity and critical to severe weather (EMLs)
14
Part II: Results - ‘warm season’ flow pattern composite
Warm_strat
72 h 48 h
24 h 0 h
K/km
500-hPa Height / Wind and 700-500-hPa Lapse Anomaly
N=14
Summary
Summary
1. Two maxima in high lapse rates over North America– Cold season - Gulf of Alaska (5565N)– Warm season - Intermountain West (3545N)
2. Seasonal variations likely associated with1. Fluctuations in the “time-mean storm track”
2. Surface-based sensible heating over elevated terrain
3. A blend of the two (especially at middle latitudes)
• Intraseasonal variations likely associated with– Synoptic-scale variability (flow patterns, disturbances, etc.)
• Albany composite analyses suggest– Cold (warm) season occurrences of high lapse rates originate in Alberta (Colorado) in conjunction with Alberta storm track (eastward advection of
high lapse rates)