Title Climatology of High Lapse Rates and Associated Synoptic-Scale Flow Patterns over North America and the Northeast US(1974  2007) Jason M. Cordeira*, Thomas J. Galarneau, Jr., and Lance F. Bosart Dept. of Earth and Atmospheric Sciences University at Albany/SUNY NROW X 6 November 2008 Albany, NY Research funded by the National Science Foundation #ATM and #ATM

Motivation Motivation -The influence of high lapse rates on severe weather 12Z 6  00Z 9 June Z/6 00Z/7 12Z/700Z/8 12Z/8 00Z/9 Hail (168/8) Wind (473/5) Tornado (22) H7-H5  Eastern extent of 700  500-hPa Lapse Rate Contour (8.0 K km  1 ) SPC event archive / RUC analyses 700  500-hPa Flow 00Z/900Z/806Z/706Z/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: 1974  2007 / 12Z (10  14Z) Accounted for “station advection” Normalized to t max = 12,418 (34 years * 365 days + leap = 12,418) Stations with <6,209 radiosonde observations not used (0.5 * t max ) 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 km  1 Potential Temperature 2. Data acquisition: [NCDC] Integrated Global Radiosonde Archive (IGRA) ftp://ftp.ncdc.noaa.gov/pub/data/igra/data-por/ Methodology  

Part I: Results - cumulative frequency distribution 1974  2007 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 50  70 days/yr 1  3 days/yr 15  25 days/yr

Part I: Results - monthly frequency distributions January 1974  2007 Jan Apr Jul Oct 5

April 1974  2007 Apr Part I: Results - monthly frequency distributions Jan Apr Jul Oct 10

July 1974  2007 July Part I: Results - monthly frequency distributions Jan Apr Jul Oct 1

October 1974  2007 Oct Part 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 May  June 3.Expansion of Intermountain maximum toward the California coast and Northern Plains July  August 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 Plains Regional Monthly Frequency Regional Frequency Month

SCP IMW Part II: Results - regional histograms Intermountain West (IMW) Intermountain West Regional Monthly Frequency Regional Frequency Month Note: y-axis scale has changed!

NW Part II: Results - regional histograms Northwest (NW) IMW Similar for Upper- Midwest Northwest Regional Monthly Frequency Regional Frequency Month Note: y-axis scale has changed!

CW Part II: Results - regional histograms Canada West (CW) NW Canada West Regional Monthly Frequency Regional Frequency Month Note: y-axis scale has changed!

NE Part II: Results - regional histograms Northeast (NE) Northeast Regional Monthly Frequency Regional Frequency Month Note: y-axis scale has changed! CW

SSV N Part II: Results - sub-seasonal variability  500-hPa Lapse Rate Hovmöller ‘Transitory’ Cold season Synoptic-scale periodicity 2.5  ECMWF Reanalysis 55  65  N Hovmöller Band  5  latitude of seasonal maximum 1 Jan 1 Mar 1 May 1 Jul 1 Sep 1 Nov 1 Jan W 150W135W120W 105W 90W K km  1

SSV S Part II: Results - sub-seasonal variability  500-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 Jan 120W 105W 90W75W60W 45W 30W K km   ECMWF Reanalysis 35  45  N Hovmöller Band ~Albany

Part II: Results - mean potential temperature N=52, hPa  -mean bin [  C] Pot_dist

Part II: Results - mean potential temperature N= hPa  -mean bin [  C] Pot_dist Albany (year) Albany AMJJAS Albany ONDJFM 1 Albany

Part II: Results - potential temperature stratification Pot strat Cold-season phenomenon Characteristics: Lower tropospheric warm advection Moist troposphere Low 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 hPa Lapse Anomaly           N=28

Part II: Results - potential temperature stratification Pot strat Warm-season phenomenon Characteristics: Originated as surface-based mixed layers over elevated terrain High 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 hPa Lapse Anomaly       N=14    

Summary 1.Two maxima in high lapse rates over North America –Cold season - Gulf of Alaska (55  65  N) –Warm season - Intermountain West (35  45  N) 2.Seasonal variations likely associated with –Fluctuations in the “time-mean storm track” –Surface-based sensible heating over elevated terrain –A blend of the two (especially at middle latitudes) 3.Intraseasonal variations likely associated with –Synoptic-scale variability (flow patterns, disturbances, etc.) 4.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)