Warm Season Dry Spells in the Central and Eastern United States: Diverging Skill in Climate Model Representation
The study objectively identifies three fundamental warm season dry spell patterns (occurring over the southern Great Plains, Midwest, and southeast US, respectively) along with the distinct large-scale meteorological patterns (LMPs) that drive them. It is determined that climate model skill in representing dry spell behavior is directly related to corresponding skill in representing the detailed nature of the organizing LMPs.
The research results provide an important constraint regarding the limitations of climate models in representing regional dry spells. Model shortcomings in representing large-scale meteorological patterns can directly carry over to the representation of regional extreme events.
Persistent warm season dry spell cases (>10 days) are identified in observations (NOAA-CPC daily data) and parallel CMIP5 simulations (CCSM4, GFDL-CM3, CCSM4, MPI-ESM-MR and EC-EARTH) for 1950-2005. A hierarchical cluster analysis is used to identify canonical dry spell spatial patterns. The associated large-scale meteorological patterns (LMPs), interannual variability and long-term trends of dry spells are examined. The reasons for model shortcomings in representing observed dry spell behavior are explored. Three fundamental dry spell patterns are identified with geographical centers located in the southern Great Plains, Midwest, and southeast US, respectively. LMPs generate dry spell events via (a) diversion of precipitation producing weather disturbances and (b) regional moisture transport suppression. Model skill in representing dry spell behavior is directly related to corresponding skill in representing the nature of the underlying LMP.