Siegfried Schubert (PI)
NASA Goddard Space Flight Center
siegfried.d.schubert@nasa.gov

Understanding and Quantifying the 1970's Climate Transition in the Presence of a Rapidly Changing Observing System

The mid-1970s are characterized by abrupt shifts in a number of physical and biological climate records (e.g., intensity of the Aleutian low, the Pacific Decadal Oscillation, various North Pacific fisheries time series, Alaskan glacier mass balances, etc.).  This period is also characterized by an apparent transition in the character of ENSO toward more intense and frequent warm events, and marks the beginning of accelerated trends in a number of geophysical parameters (e.g., surface temperature and precipitation) over various regions of North America.  The introduction of satellite observations also makes the 1970s a period of major change in the global climate observing system.  These changes to the observing system have unfortunately had substantial impacts on the temporal consistency of the first generation of reanalysis products, limiting their value for addressing the nature and scope of the 1970s climate shift.  The goals of this proposal are to 1) provide substantially improved estimates of the global extent of the 1970s climate transition, and to 2) improve our understanding of the fundamental cause(s) of the shift.  It is proposed to use the next generation GMAO (GEOS-5) data assimilation system to carry out experiments designed to assess the sensitivities of the reanalysis products to the changing observing system.  Adaptive bias correction techniques will be tested to evaluate their effectiveness in correcting observational bias during a period of abrupt climate change.  AMIP-style simulations will be carried out to isolate the SST contributions to the atmospheric climate shift.  The impact of model errors will be assessed by running the AMIP experiments with a number of different AGCMs, and by rerunning selected observing system experiments in which the GEOS5 AGCM is swapped with the NCEP model.  The GMAO ocean data assimilation system will be used to carry out ocean forcing experiments designed to determine the causes of the 1970s SST anomalies.  This work is highly relevant to the ESE research questions on climate variability and change: How well can transient climate variability by assessed and predicted? How well can long-term climate trends be assessed and predicted?  The work also contributes directly to the near-term CCSP deliverable: “Reanalyses of historical climate data for key atmospheric features; implications for attribution of causes of observed change”, and serves to enhance the value of the NASA MERRA project (funded to produce a reanalysis for the period 1979 onwards).

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