1 observed changes in heavy precipitation events and extratropical cyclones david r. easterling 1,...
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Observed Changes in Heavy Precipitation Events and Extratropical
CyclonesDavid R. Easterling1, Kenneth E. Kunkel2,
David Kristovitch3, Scott Applequist1, Leslie Stoecker3, Byron Gleason1, Rebecca Smith4
1NOAA/National Climatic Data Center, Asheville, NC2CICS/NOAA/National Climatic Data Center, Asheville, NC3Illinois State Water Survey, Champaign, IL4Colorado State University, Ft. Collins, CO
Supported by the NOAA Climate Program Office
Outline
Meteorological causes of observed changes in heavy precipitation events in the USA.
Changes in extra-tropical cyclones over the Northern Hemisphere.
Updated from Kunkel, K. E., D.R. Easterling, K. Redmond, and K. Hubbard, 2003: Temporal variations of extreme precipitation events in the United States: 1895–2000, Geophys. Res. Lett., 30, 1900,
10.1029/2003GL018052
What’s Causing The Increase?
Have there been secular changes in the frequency, intensity, and other characteristics of the meteorological phenomena producing heavy precipitation?
Are the recent increases primarily a result of increases in atmospheric water vapor concentrations?
Or some combination of the above?
U.S. Climate Data
U.S. Cooperative Observer Network in operation since late 1880s, used 935 long-term stations.
Daily Observations – Max and Min Temperature, Precipitation, Snowfall, Snow Depth
Extremes Definition
Event Duration – days Recurrence (threshold exceedance) –
years 1-day duration, 5-year recurrence
Meteorological Types
Extratropical Cyclones− Frontal (at least ~300 km away from
center of surface or upper low)− ETC (near surface or upper low center)
Tropical Cyclones Mesoscale Convective Systems Air Mass Convection Southwest Monsoon Upslope
Data Sources For Synoptic Types Reanalysis pressure and
temperature Tropical Cyclone tracks Surface fields of temperature and
precipitation Daily weather maps Identification of types mostly based
on judgment of authors.
Contribution of Tropical Cyclones
HURDAT tropical cyclone tracks dataset
Heavy precipitation event considered to be caused by tropical cyclone if it occurred within 5 degrees of track
Southeast
0.00
0.05
0.10
0.15
0.20
1909-1910
1911-1920
1921-1930
1931-1940
1941-1950
1951-1960
1961-1970
1971-1980
1981-1990
1991-2000
2001-2006
Decade
Nu
mb
er o
f H
eavy
Eve
nts
/Sta
tio
n
ETC Frontal Monsoon Air Mass MCC Upslope TC
Frontal
TC
Extra-tropical Cyclones: have ETC tracks shifted and have they become more intense?
Use the 100+ year Historical Re-analysis being run by NOAA/Earth System Research Lab.
Sea-level pressure, 2o grid, 6h, 56 ensemble members
ETCs defined as local minimum, surrounded by +2 hPa contour.
McCabe, G. J., M. P. Clark, and M. C. Serreze, 2001: Trends in Northern Hemisphere
surface cyclone frequency and intensity. Journal of Climate, 14, 2763-2768.
NH Mid-latitude cyclone frequency, normalized by 1959-97 mean & std dev.
Tracked ETC counts for winter season (Nov-Mar)
ending in the year indicated.
CONCLUSIONS
The observed national upward trend in heavy precipitation frequency is due primarily to trends during June through October
Statistically significant upward trends in the # of events caused by frontal systems and tropical cyclones
Upward trends in tropical cyclone events in all Atlantic and Gulf regions except for Florida
Extratropical Cyclones
Results from NOAA Historical Reanalysis compare well with previous analyses for post 1950 period.
If pre-1950 period included relative increase from 1900-1950 for mid-latitudes, relative decline from 1920s for high latitudes.