A new methodology for identifying daughter cyclogenesis: application for the Mediterranean Basin

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An evaluation of 23 models, participating in the Coupled Model Inter‐comparison Project phase 5 (CMIP5), in representing extreme precipitation indices (EPI), over the Eastern Mediterranean (EM) and the Fertile Crescent (FC), was performed. The models ensemble was then used to predict the EPIs evolution in the 21st century under (Representative Concentration Pathway, RCP) RCP4.5 and RCP8.5 scenarios. Models' performance was determined with respect to gridded precipitation observations from the APHRODITE project. The ensemble mean was found to perform relatively well in capturing the EM steep precipitation gradient, the FC structure and the EPI trends in the observations period (1970–2000). Over the EM, CMIP5 models agree on a future decrease in the following three EPIs; total precipitation (TP), consecutive wet days, and number of wet days by the values of 20–35%, 10–20%, and 20–35%, respectively. In the FC, extremely wet days (P95) are expected to increase by approximately 25%, except for the south eastern coasts of the Mediterranean Sea, which show significant decreases in P95, particularly for RCP8.5 and at the end of the 21st century. Hence, while TP is expected to decrease, extreme precipitation is expected to increase, at least for the north‐eastern part of the FC. This will significantly influence agriculture and floods' potential in a region already suffering from political unrest. The changes in EPIs are related to changes in the synoptic patterns over the EM, especially the predicted changes in cyclones frequency and intensity in the 21st century, due to changes in storm tracks governed by the phase of the North Atlantic Oscillation and the expected expansion of the Hadley Cell towards the poles in a warmer climate.

Section: Introductionmentioning

confidence: 99%

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

Samuels

Hochman

Baharad

et al. 2017

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“…Figure (a) displays a composite map of DCs formed over the Gulf of Genoa, on the cold front located east of the parent. The map reflects the well‐known features of Genoa low genesis (see Figure (b) in Buzzi and Tibaldi, and Figure 8(a) in Ziv et al , ). Each DC is formed behind its parent, within the northwesterly flow which is perpendicular to the mountain barrier responsible for the Lee effect.…”

Section: Resultsmentioning

confidence: 72%

“…The study period includes the winter seasons December‐February (DJF) during 33 years, between 1979–1980 and 2011–2012. We have used the database of the cyclones archive (Ziv et al , ), which was derived from the ERA‐Interim reanalysis (Uppala et al , ; European Centre for Medium‐Range Weather Forecasts, ; Dee et al , ), with 6‐h temporal resolution and 0.75° × 0.75° spatial resolution. This archive contains all DCs with life duration greater or equal to 24 h, and details of the parent of each cyclone.…”

Section: Methodsmentioning

confidence: 99%

“…Thermal DCs can also form within the warm sector of their PCs (Figure 1(c)). Ziv et al (2015) were the first to develop an algorithm for parent-daughter identification, and they applied their methodology to MCs. In addition to detecting and tracking cyclones, their method maps the area of influence of existing cyclones, which is the region where DCs are formed.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A new classification algorithm for daughter cyclone formation with respect to the parent's frontal system – application for the Mediterranean Basin

Saaroni

Harpaz

Ziv

2016

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This article presents a semi-objective methodology to classify formation scenarios of a new 'daughter' cyclone (DC), based on the thermal field characteristics of the parent cyclone (PC). An automated algorithm assigns a DC to one of seven formation types, according to the following considerations: Whether the DC is formed on a front belonging to the parent's frontal system or to a different frontal system, and whether this frontal system is cold, warm or quasi-stationary. An additional type contains DCs formed within the warm sector of the parent. The algorithm uses measures derived from wind and temperature fields at 850-hPa: the temperature gradient, the temperature advection and the temperature Laplacian, each computed at the formation location of the DC, and also the temperature difference between the DC and the PC. The classification method was applied to 4303 Mediterranean DCs which were observed during 33 winters. Totally 85% of the DCs were identified as belonging to one of the seven predefined types, implying that the formation of the remaining 15% was not related to baroclinic or thermal factors. Among the successfully classified DCs, over half were formed on the frontal system of the parent, a third of the DCs on a separate frontal system and only 13% were formed within the warm sector. Most of the 'cold front' cyclones were formed at the major Mountain Lee locations, whereas those formed on warm fronts were generated mostly over the Adriatic, Ligurian and Aegean Seas. Inspection of composite maps of distinct formation types in various regions revealed unique formation scenarios, like DCs forming over western Morocco but belonging to third generation Genoa Lows. Other reflects discontinuous movement of cyclones, resulting from encounter with topographical obstacles, found mostly on PCs' warm fronts, or from the attraction of cyclogenetic areas left behind, mostly on PCs' cold fronts.

“…The region's climate is intensely affected by external forcing of both mid-latitude and tropical origins (e.g., Alpert et al, 2005). However, the rain in the Mediterranean part of Israel results mainly from passage or development of extratropical cyclones over the eastern Mediterranean, known as the Cyprus Lows (HMSO, 1962;Sharon and Kutiel, 1986;Alpert et al, 1990;Shay-El and Alpert, 1991;Trigo et al, 1999;Schädler and Sasse, 2006;Ziv et al, 2006Ziv et al, , 2015. Saaroni et al (2010a) found that the average contribution of Cyprus Lows to the rainfall in Israel is 83%.…”

Section: Introductionmentioning

confidence: 99%

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

Hochman

Kunin

Alpert

et al. 2019

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Global climate models provide only partial information on local‐scale phenomenon, such as precipitation, primarily due to their coarse resolution. In this study, statistical downscaling algorithms, based on both weather regimes and past analogues, are operated for 18 Israeli rain gauges with an altitude ranging between −200 and ~1,000 m above sea level (ASL). To project seasonal precipitation over Israel and its hydrologic basins, the algorithms are applied to six Coupled Model Inter‐comparison Project Phase 5 (CMIP5) models for the end of the 21st century, according to the RCP4.5 and RCP8.5 scenarios. The downscaled models can capture quite well the seasonal precipitation distribution, though with underestimation in winter and overestimation in spring. All models display a significant reduction of seasonal precipitation for the 21st century according to both scenarios. The winter reductions for the end of the century and the RCP8.5 scenario are found to be ~22 and ~37% according to the weather regimes and the analogues downscaling methods, respectively. Spring reductions are found to be ~10–20% larger than winter reductions. It is shown that the projected reduction results from a decrease in the frequency of the rain‐bearing systems, as well as a decrease in the average daily precipitation intensity. The areas with the largest reductions in seasonal precipitation are found over the central mountains, the Mediterranean coastal area, and the Sea of Galilee hydrologic basins, which are the main fresh‐water aquifers and reservoirs of Israel. The statistical downscaling methods applied in this study can be easily transferred to other regions where long‐term data sets of observed precipitation are available. This study and others may serve as a basis for priority and policy setting toward better climate adaptation with associated uncertainties related to the methods used and nonstationary of the climate system.