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