The Response of the Northern Hemisphere Storm Tracks and Jet Streams to Climate Change in the CMIP3, CMIP5, and CMIP6 Climate Models

Abstract

The representation of the Northern Hemisphere (NH) storm tracks and jet streams and their response to climate change have been evaluated in climate model simulations from Phases 3, 5, and 6 of the Coupled Model Intercomparison Project (CMIP3, CMIP5, and CMIP6, respectively). The spatial patterns of the multimodel biases in CMIP3, CMIP5, and CMIP6 are similar; however, the magnitudes of the biases in the CMIP6 models are substantially lower. For instance, the multimodel mean RMSE of the North Atlantic storm track for the CMIP6 models (as measured by time-filtered sea-level pressure variance) is over 50% smaller than that of the CMIP3 models in both winter and summer, and over 40% smaller for the North Pacific. The magnitude of the jet stream biases is also reduced in CMIP6, but by a lesser extent. Despite this improved representation of the current climate, the spatial patterns of the climate change response of the NH storm tracks and jet streams remain similar in the CMIP3, CMIP5, and CMIP6 models. The SSP2-4.5 scenario responses in the CMIP6 models are substantially larger than in the RCP4.5 CMIP5 models, which is consistent with the larger climate sensitivities of the CMIP6 models compared to CMIP5.

Larger spatial footprint of wintertime total precipitation extremes in a warmer climate

“…Wintertime precipitation extremes in this region are typically driven by an anomalously strong jet stream configuration over the United Kingdom (Figure 3d) and associated storminess. Under a 2.0 °C warming scenario, a significant strengthening of such a configuration (Figure 3f; compare with Figure 3d) would, therefore, favor the substantial increase in precipitation extremes and associated spatial extents (Figure 3e; see also more frequent stippling compared to Figure 3d) (Harvey et al, 2020;Li et al, 2018;Zappa et al, 2013). We observe that given that precipitation over the Scandinavian Peninsula is mainly driven by cyclones (Hawcroft et al, 2012;Pfahl & Wernli, 2012) and a sustained jet stream is associated with an increased cyclone activity, such an atmospheric circulation change would be consistent with a strengthening of the regional cyclonic activity (Harvey et al, 2020;Pinto et al, 2007;Zappa et al, 2013).…”

“…The largest spatial scale extremes occur over northern Europe, Russian plains, eastern China, and oceans; that is, typically over extended low altitude areas, where the occurrence of widespread precipitation extremes is not obstructed by the orography. For example, in Moscow (Russia), the most extended events are associated with an anomalous seasonal upper-level atmospheric jet over central Europe (Figure S3) and associated cyclonic activity, which-given the flat topography-favors widespread precipitation extremes in the surrounding area (Harvey et al, 2020;Hawcroft et al, 2012). The mean altitude of the locations with the top 5% (1%) spatial scale extremes is 130 m (80 m), against an average altitude of 370 m over the analyzed area.…”

“…To begin with, the strong reduction in precipitation magnitudes over northern Africa (about −10% in Marrakesh; Morocco)-which contributes to the reduced extents of the spatial scale extremes in the surrounding region-is in line with documented changes in the atmospheric circulation that would reduce both daily precipitation extremes (Pfahl et al, 2017) and total wintertime precipitation (Zappa & Shepherd, 2017). In fact, in Marrakesh, sustained upper-level winds over northern Africa, which are associated with stormy weather (Harvey et al, 2020;Zappa, Hoskins, et al, 2015), favor high precipitation amounts around the city, northwestern Africa, and the central and western Mediterranean region (Figure 3a). In a warmer climate, this atmospheric circulation feature is expected to significantly weaken both during extremely wet winters and on average (Figure 3c; compare with Figure 3a), which is in line with a documented weakening and reduction of storm intensity and frequency Harvey et al, 2020;Pinto et al, 2007;Zappa, Hawcroft, et al, 2015).…”

“…In fact, in Marrakesh, sustained upper-level winds over northern Africa, which are associated with stormy weather (Harvey et al, 2020;Zappa, Hoskins, et al, 2015), favor high precipitation amounts around the city, northwestern Africa, and the central and western Mediterranean region (Figure 3a). In a warmer climate, this atmospheric circulation feature is expected to significantly weaken both during extremely wet winters and on average (Figure 3c; compare with Figure 3a), which is in line with a documented weakening and reduction of storm intensity and frequency Harvey et al, 2020;Pinto et al, 2007;Zappa, Hawcroft, et al, 2015). As a result, precipitation extreme magnitudes and extents would decrease (Figure 3b; see also the reduced stippling around Marrakesh compared to Figure 3a), despite a higher atmospheric moisture content (Li et al, 2018;Pfahl et al, 2017).…”

Are Cut-off Lows Simulated Better in CMIP6 Compared to CMIP5 ?

“…The Coupled Model Intercomparison Project (CMIP) has facilitated the assessment of the impact of past, present and future climate conditions on large and synoptic scale weather patterns (Bellenger et al 2014;Zappa et al 2013;Reboita et al 2019;Harvey et al 2020), providing an invaluable source for the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports. Data from the sixth generation of CMIP is now available, and represents the current state-of-the-art in global coupled climate modeling.…”