| 1. |
- Hochman, Assaf, et al.
(författare)
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A new dynamical systems perspective on atmospheric predictability : Eastern Mediterranean weather regimes as a case study
- 2019
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- The atmosphere is a chaotic system displaying recurrent large-scale configurations. Recent developments in dynamical systems theory allow us to describe these configurations in terms of the local dimension-a proxy for the active number of degrees of freedom-and persistence in phase space, which can be interpreted as persistence in time. These properties provide information on the intrinsic predictability of an atmospheric state. Here, this technique is applied to atmospheric configurations in the eastern Mediterranean, grouped into synoptic classifications (SCs). It is shown that local dimension and persistence, derived from reanalysis and CMIP5 models' daily sea-level pressure fields, can serve as an extremely informative qualitative method for evaluating the predictability of the different SCs. These metrics, combined with the SC transitional probability approach, may be a valuable complement to operational weather forecasts and effective tools for climate model evaluation. This new perspective can be extended to other geographical regions.
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| 2. |
- Hochman, Assaf, et al.
(författare)
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The dynamics of cyclones in the twentyfirst century : the Eastern Mediterranean as an example
- 2020
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 54:1-2, s. 561-574
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Tidskriftsartikel (refereegranskat)abstract
- The Mediterranean region is projected to be significantly affected by climate change through warming and drying. The Eastern Mediterranean (EM) is particularly vulnerable since the bulk of the precipitation in the region is associated with a specific circulation pattern, known as Cyprus Low (CL). Here, we study the influence of increased greenhouse gases on the average properties and dynamics of CLs, using a regional semi-objective synoptic classification. The classification is applied to NCEP/NCAR reanalysis data for the present day (1986-2005) as well as to eight CMIP5 models for the present day and for the end of the century (2081-2100; RCP8.5). This is complemented by a dynamical systems analysis, which is used to investigate changes in the dynamics and intrinsic predictability of the CLs. Finally, a statistical downscaling algorithm, based on past analogues, is applied to eighteen rain stations over Israel, and is used to project precipitation changes associated with CLs. Significant changes in CL properties are found under climate change. The models project an increase in CL meridional pressure gradient (0.5-1.5 hPa/1000 km), which results primarily from a strong increase in the pressure over the southern part of the study region. Our results further point to a decrease in CL frequency (- 35%, as already noted in an earlier study) and persistence (- 8%). Furthermore, the daily precipitation associated with CL occurrences over Israel for 2081-2100 is projected to significantly reduce (- 26%). The projected drying over the EM can be partitioned between a decrease in CL frequency ( 137 mm year(-1)) and a reduction in CL-driven daily precipitation ( 67 mm year(-1)). The models further indicate that CLs will be less predictable in the future.
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