Patterns of Precipitation Change and Climatological Uncertainty among CMIP5 Models, with a Focus on the Midlatitude Pacific Storm Track*

Abstract

Projections of modeled precipitation (P) change in global warming scenarios demonstrate marked intermodel disagreement at regional scales. Empirical orthogonal functions (EOFs) and maximum covariance analysis (MCA) are used to diagnose spatial patterns of disagreement in the simulated climatology and end-of-century P changes in phase 5 of the Coupled Model Intercomparison Project (CMIP5) archive. The term principal uncertainty pattern (PUP) is used for any robust mode calculated when applying these techniques to a multimodel ensemble. For selected domains in the tropics, leading PUPs highlight features at the margins of convection zones and in the Pacific cold tongue. The midlatitude Pacific storm track is emphasized given its relevance to wintertime P projections over western North America. The first storm-track PUP identifies a sensitive region of disagreement in P increases over the eastern midlatitude Pacific where the storm track terminates, related to uncertainty in an eastward extension of the climatological jet. The second PUP portrays uncertainty in a zonally asymmetric meridional shift of storm-track P, related to uncertainty in the extent of a poleward jet shift in the western Pacific. Both modes appear to arise primarily from intermodel differences in the response to radiative forcing, distinct from sampling of internal variability. The leading storm-track PUPs for P and zonal wind change exhibit similarities to the leading uncertainty patterns for the historical climatology, indicating important and parallel sensitivities in the eastern Pacific storm-track terminus region. However, expansion coefficients for climatological uncertainties tend to be weakly correlated with those for end-of-century change.

Relationships among climatological vertical moisture structure, column water vapor, and precipitation over the central Amazon in observations and CMIP5 models

“…We next evaluate the spread in AMIP ensemble q profiles by applying a multimodel analysis referred to as principal uncertainty patterns (PUPs) [see Langenbrunner et al, 2015;Lintner et al, 2016]. For our purposes here, we use empirical orthogonal function (EOF) analysis as the basis for computing PUPs.…”

Uncertainty in future projections of the North Pacific subtropical high and its implication for California winter precipitation change

“…Consistent with Langenbrunner et al . [, Figure 7a], Figure a indicates that the intermodel spread in the projected change in the E‐NPSH latitude is strongly associated with uncertainty in the SST change over the western North Pacific instead of the eastern North Pacific. Such SST pattern resembles a Pacific Decadal Oscillation (PDO)‐like sea surface temperature signature in the midlatitudes.…”

“…For instance, the models with a negative sign of PC of SST, their future projection shows the SST warming (not PDO‐like cooling) but with a relatively weak magnitude compared to the MME mean. The leading mode, which explains 62.3% of the total squared covariance, resembles a PDO‐like pattern as shown in Figure a [see also Langenbrunner et al ., , Figure 7a]. The magnitude of warming reaches 0.12 K/decade near the Kuroshio‐Oyashio extension region.…”

“…Our result is consistent with the recent studies relating California winter precipitation change in a warmer climate to large‐scale features such as the storm track and Pacific jet extent [ Chang et al ., ; Langenbrunner et al ., ]. A consensus emerging from these studies is that the uncertainty in the future wintertime California precipitation is much greater than the intermodel agreement, a factor that must be taken into consideration in the planning for adaptation and mitigation to the projected hydroclimate changes in California.…”

Characterizing CMIP5 model spread in simulated rainfall in the Pacific Intertropical Convergence and South Pacific Convergence Zones

“…[2015] performed a multivariate PUP analysis to relate CMIP5-simulated trends in SST to trends in land surface precipitation, while Langenbrunner et al [2015] applied PUP analysis to identify and attribute CMIP5 model discrepancies in the simulated meridional position and longitudinal extent of the North Pacific storm track in current climate as well as end of the 21st century projections.…”