Contemporaneous and Antecedent Links of Atlantic and Pacific Circulation Features with North American Hydroclimate: Structure and Interannual Variability Scott J. Weaver Megan E. Linkin Link to Mid-term presentation

Motivation/Objective Natural modes of variability in both the Atlantic and Pacific basins generate anomalous large scale circulation patterns. Natural modes of variability in both the Atlantic and Pacific basins generate anomalous large scale circulation patterns. These patterns can result in anomalous temperature and moisture advection over North America. These patterns can result in anomalous temperature and moisture advection over North America. Attempted to ascertain the leading modes of variability in both MAM and JJA Attempted to ascertain the leading modes of variability in both MAM and JJA Obtain spatio- temporal structure of these patterns Obtain spatio- temporal structure of these patterns Determine antecedent links between spring and summer Determine antecedent links between spring and summer

Methodology/Data Performed traditional and extended empirical orthogonal function analysis (EOF and EEOF) on sea level pressure anomalies over each individual ocean basin Performed traditional and extended empirical orthogonal function analysis (EOF and EEOF) on sea level pressure anomalies over each individual ocean basin Regressed geopotential height anomalies to establish circulation anomalies Regressed geopotential height anomalies to establish circulation anomalies Regressed multiple hydroclimate variables to determine remote influences on soil moisture, moisture flux convergence and precipitation Regressed multiple hydroclimate variables to determine remote influences on soil moisture, moisture flux convergence and precipitation NCEP/NCAR monthly reanalysis used to diagnose circulation NCEP/NCAR monthly reanalysis used to diagnose circulation NARR used to diagnose hydroclimate anomalies NARR used to diagnose hydroclimate 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 1988 ENSO ending a cycle ENSO ending a cycle Shifts in convection centers in tropics induced an anomalous wave train in the upper troposphere Shifts in convection centers in tropics induced an anomalous wave train in the upper troposphere Resulted in a ridge positioned over the Great Plains Resulted in a ridge positioned over the Great Plains Ridge suppressed precipitation during summer months Ridge suppressed precipitation during summer months An already dry spring was followed by a dry summer An already dry spring was followed by a dry summer Land surface processes served to exacerbate the situation Land surface processes served to exacerbate the situation

Warm ENSO events cause an increase in precipitation in Great Plains region. During JJA1993, a long warm ENSO event was occurring ( ) Nino3.4 index was greater than zero from Resulted in anomalously large amounts of precipitation over central US Courtesy of CPC/NOAA

Summer 1993 Persistent ENSO event resulted in numerous seasons with anomalous precipitation Persistent ENSO event resulted in numerous seasons with anomalous precipitation Plenty of soil moisture present from past seasons Plenty of soil moisture present from past seasons Continuing warm ENSO conditions supplied dynamics for enhanced precipitation Continuing warm ENSO conditions supplied dynamics for enhanced precipitation NAO index was negative both spring and summer of 1993 NAO index was negative both spring and summer of 1993 Nothing to suppress anomalous precipitation that was occurring Nothing to suppress anomalous precipitation that was occurring

Future Work Assess Pacific Basin effect on MAM hydroclimate Assess Pacific Basin effect on MAM hydroclimate Perform statistical analysis to determine if patterns and teleconnections are significant Perform statistical analysis to determine if patterns and teleconnections are significant Investigate possible potential predictability of any mode (“Shanghai express”) due to its relationship with SST Investigate possible potential predictability of any mode (“Shanghai express”) due to its relationship with SST