Influence of Atmospheric Errors on Weeks 2-4 California Current System Predictions | CU Experts

Abstract; Understanding the forecast skill of ocean state anomalies on subseasonal timescales is critical for the effective use of ocean forecasts in marine resource management. Here, we evaluate error propagation in the European Center for Medium-range Weather Forecasting subseasonal-to-seasonal (S2S) coupled forecast system, specifically examining how atmospheric errors impact the accuracy of California Current System (CCS) ocean forecasts. Ensemble Sensitivity Analysis reveals regions where early lead-time atmospheric conditions can influence upper-ocean forecast errors, particularly in sea surface temperature and mixed layer depth. Conditioning on ensemble members with smaller atmospheric errors during the first 1-4 lead days, yields a reduction in CCS errors for lead weeks 2-4 which is statistically significant for weeks 2-3. Improvements in the strength of both low and high pressure systems lead to better representation of near surface along-shore winds, which constitutes improved atmospheric forcing of CCS ocean conditions. Here, we show how atmospheric weather patterns modulate the upper CCS by diagnosing the propagation of model errors in an operational S2S coupled forecast system. These results suggest that identifying more predictable atmospheric states early in the forecast can lead to more accurate CCS predictions for weeks 2-3.

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