Contemporaneous and Antecedent Links of Atlantic and Pacific Circulation Features with North...
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Transcript of Contemporaneous and Antecedent Links of Atlantic and Pacific Circulation Features with North...
Contemporaneous and Antecedent Links of Atlantic and Pacific Circulation Features with North American Hydroclimate: Structure and Interannual Variability
Scott J. WeaverScott J. Weaver
Megan E. LinkinMegan E. Linkin
Link to Mid-term presentation
Motivation/ObjectiveMotivation/Objective
Natural modes of Natural modes of variability in both the variability in both the Atlantic and Pacific Atlantic and Pacific basins generate basins generate anomalous large scale anomalous large scale circulation patterns.circulation patterns.
These patterns can These patterns can result in anomalous result in anomalous temperature and temperature and moisture advection moisture advection over North America.over North America.
Attempted to Attempted to ascertain the leading ascertain the leading modes of variability modes of variability in both MAM and JJAin both MAM and JJA
Obtain spatio-Obtain spatio-temporal structure of temporal structure of these patternsthese patterns
Determine Determine antecedent links antecedent links between spring and between spring and summersummer
Methodology/DataMethodology/Data
Performed traditional Performed traditional and extended and extended empirical orthogonal empirical orthogonal function analysis (EOF function analysis (EOF and EEOF) on sea and EEOF) on sea level pressure level pressure anomalies over each anomalies over each individual ocean basinindividual ocean basin
Regressed Regressed geopotential height geopotential height anomalies to establish anomalies to establish circulation anomaliescirculation anomalies
Regressed multiple Regressed multiple hydroclimate variables hydroclimate variables to determine remote to determine remote influences on soil influences on soil moisture, moisture moisture, moisture flux convergence and flux convergence and precipitationprecipitation
NCEP/NCAR monthly NCEP/NCAR monthly reanalysis used to reanalysis used to diagnose circulationdiagnose circulation
NARR used to NARR used to diagnose hydroclimate diagnose hydroclimate anomalies anomalies
Springtime positive NAO phase characterized by broad longitudinal ridge
Would suppress precipitation and result in anomalously warm temperatures
Also displaced jet stream further north
Antecedent condition for summertime drought
In 1988, NAO was positive during MAM
Courtesy of CPC/NOAA
Summer 1988Summer 1988
ENSO ending a cycleENSO ending a cycle Shifts in convection Shifts in convection
centers in tropics centers in tropics induced an induced an anomalous wave anomalous wave train in the upper train in the upper tropospheretroposphere
Resulted in a ridge Resulted in a ridge positioned over the positioned over the Great PlainsGreat Plains
Ridge suppressed Ridge suppressed precipitation during precipitation during summer monthssummer months
An already dry An already dry spring was followed spring was followed by a dry summerby a dry summer
Land surface Land surface processes served processes served to exacerbate the to exacerbate the situationsituation
Warm ENSO events cause an increase in precipitation in Great Plains region.
During JJA1993, a long warm ENSO event was occurring (1992-1994)
Nino3.4 index was greater than zero from 1990-1995
Resulted in anomalously large amounts of precipitation over central US
Courtesy of CPC/NOAA
Summer 1993Summer 1993
Persistent ENSO event Persistent ENSO event resulted in numerous resulted in numerous seasons with seasons with anomalous precipitationanomalous precipitation
Plenty of soil moisture Plenty of soil moisture present from past present from past seasonsseasons
Continuing warm ENSO Continuing warm ENSO conditions supplied conditions supplied dynamics for enhanced dynamics for enhanced precipitationprecipitation
NAO index was NAO index was negative both spring negative both spring and summer of 1993and summer of 1993
Nothing to suppress Nothing to suppress anomalous anomalous precipitation that was precipitation that was occurringoccurring
Future WorkFuture Work
Assess Pacific Basin effect on MAM Assess Pacific Basin effect on MAM hydroclimatehydroclimate
Perform statistical analysis to Perform statistical analysis to determine if patterns and determine if patterns and teleconnections are significantteleconnections are significant
Investigate possible potential Investigate possible potential predictability of any mode predictability of any mode (“Shanghai express”) due to its (“Shanghai express”) due to its relationship with SSTrelationship with SST