Synoptic classification in 21st century CMIP5 predictions over the Eastern Mediterranean with focus on cyclones

Abstract

The semi‐objective synoptic classification was used to investigate future changes in the occurrence of EM synoptic types, with an emphasis on Cyprus Lows (CL). A significant reduction in CL occurrence is found towards the end of the 21st century. The reductions in CLs are accompanied by an increase in the frequencies of Red Sea Troughs and Highs in winter. The predicted changes in the occurrence of various synoptic types will lead to a more accurate forecast of climatic hazards. The eight CMIP5 models average ensemble of winter (DJF) synoptic group frequencies (in %: Lows, Cyprus Lows; RST, Red Sea Troughs; PT, Persian Troughs; H, Highs) for the historic (1986–2005), mid‐century (2046–2065) and end of the century (2081–2100) periods for RCP4.5 and RCP8.5 scenarios. The NCEP synoptic classification is shown for reference.

Weather regimes and analogues downscaling of seasonal precipitation for the 21st century: A case study over Israel

“…Due to the absence of 12UTC data at the 1,000‐hPa level in CMIP5 models, we use U and V wind components and temperature from the 850‐hPa level, as well as sea level pressure (SLP). The compatibility between the 1,000 and the 850‐hPa levels, and that of the 12UTC with daily classifications was examined by Hochman et al (, c) and Berkovic (), respectively, and was shown to fit well. Nevertheless, the ability of the two downscaling methods used, that is, the modified algorithm for the synoptic classification (the “weather regimes”) and the “analogues” to downscale observed seasonal precipitation is evaluated here for both the NCEP/NCAR reanalysis and the CMIP5 models.…”

“…However, it should be stressed that precipitation is highly parametrized in the GCMs, therefore, this should not influence our findings. We suggest that the overestimation in the frequency of wet days and the underestimation of the daily precipitation may be mostly related to the general overestimation of the frequency of Cyprus Lows over the eastern Mediterranean (Hochman et al, ) and the location and depth of these cyclones in the GCMs. These features exert a strong control on daily precipitation over Israel (Saaroni et al, ).…”

“…Two statistical downscaling methods are applied, one is based on the regional weather types, that is, weather regimes (Rostkier‐Edelstein et al, ; Hochman et al, ) and the other, on analogues (Rostkier‐Edelstein et al, ). The downscaling algorithms, applied to the present period, for the NCEP/NCAR reanalysis and the CMIP5 models, were found to reproduce reasonably well the differences in the precipitation amounts between the seasons and between the hydrologic basins.…”

“…These models were previously utilized in Hochman et al (, c, and 2019) (list of models see Table ) and their ability to simulate annual and extreme precipitation indices over the eastern Mediterranean was previously presented by Samuels et al (). Furthermore, these models' ability to simulate the annual cycle of the prevailing eastern Mediterranean synoptic systems, their frequencies, and dynamics for the historical period were presented in Hochman et al (, c, and 2019). These authors concluded that the evaluation of CMIP5 models suggests that the models capture a number of the salient qualitative features found in reanalysis data.…”

Evaluation and projection of extreme precipitation indices in the Eastern Mediterranean based on CMIP5 multi‐model ensemble

“…Thus, the 1‐mm threshold for number of wet days and number of CWD is reasonable coinciding with Hochman et al . (), which found that about 20% of the days are classified as precipitation producing systems (Goldreich, ).…”