The role of the interaction between polar and subtropical jet in a case of depression rejuvenation over the Eastern Mediterranean

Prezerakos, N. G.; Flocas, Helena A.; Brikas, D.

doi:10.1007/s00703-005-0142-y

Cited by 28 publications

(25 citation statements)

References 20 publications

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“…8 highlights a first configuration, affecting the southern stations of WM, with the subtropical jet stream characterised by an axis parallel to the African coastline. In the second case, the interaction between the polar jet stream (or eddy driven jet stream) with the subtropical jet is evident and implies that the WM is on a strong divergence region; a similar mechanism was also found in the case of cyclogenesis over north-western Africa (Prezerakos et al, 2006).…”

Section: Resultssupporting

confidence: 60%

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Toreti

Xoplaki

Maraun

et al. 2010

Nat. Hazards Earth Syst. Sci.

158

135

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Abstract.We present an analysis of daily extreme precipitation events for the extended winter season (OctoberMarch) at 20 Mediterranean coastal sites covering the period . The heavy tailed behaviour of precipitation extremes and estimated return levels, including associated uncertainties, are derived applying a procedure based on the Generalized Pareto Distribution, in combination with recently developed methods. Precipitation extremes have an important contribution to make seasonal totals (approximately 60% for all series). Three stations (one in the western Mediterranean and the others in the eastern basin) have a 5-year return level above 100 mm, while the lowest value (estimated for two Italian series) is equal to 58 mm. As for the 50-year return level, an Italian station (Genoa) has the highest value of 264 mm, while the other values range from 82 to 200 mm. Furthermore, six series (from stations located in France, Italy, Greece, and Cyprus) show a significant negative tendency in the probability of observing an extreme event. The relationship between extreme precipitation events and the large scale atmospheric circulation at the upper, mid and low troposphere is investigated by using NCEP/NCAR reanalysis data. A 2-step classification procedure identifies three significant anomaly patterns both for the western-central and eastern part of the Mediterranean basin. In the western Mediterranean, the anomalous southwesterly surface to mid-tropospheric flow is connected with enhanced Correspondence to: A. Toreti (toreti@giub.unibe.ch) moisture transport from the Atlantic. During ≥5-year return level events, the subtropical jet stream axis is aligned with the African coastline and interacts with the eddy-driven jet stream. This is connected with enhanced large scale ascending motions, instability and leads to the development of severe precipitation events. For the eastern Mediterranean extreme precipitation events, the identified anomaly patterns suggest warm air advection connected with anomalous ascent motions and an increase of the low-to mid-tropospheric moisture. Furthermore, the jet stream position (during ≥5-year return level events) supports the eastern basin being in a divergence area, where ascent motions are favoured. Our results contribute to an improved understanding of daily precipitation extremes in the cold season and associated large scale atmospheric features.

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Section: Resultssupporting

confidence: 60%

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Toreti

Xoplaki

Maraun

et al. 2010

Nat. Hazards Earth Syst. Sci.

158

135

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“…Many of the Mediterranean climate characteristics are associated with the upper‐air circulation [ Chaboureau and Claud , 2006; Cullen et al , 2002; Dünkeloh and Jacobeit , 2003; Eshel and Farrell , 2000; Hurrell and Van Loon , 1997; Prezerakos et al , 2006; Quadrelli et al , 2001; Xoplaki et al , 2004]. As a result, the Mediterranean climates experience a strong influence of the North Atlantic climate modes such as the North Atlantic Ridge (RDG), the Greenland‐Scandinavia (GS), and both North Atlantic Oscillation (NAO) modes [ Cassou et al , 2004; Fil and Dubus , 2005; Quadrelli et al , 2001].…”

Section: Introductionmentioning

confidence: 99%

Temperature and productivity influences on U₃₇^K′ and their possible relation to solar forcing of the Mediterranean winter

Versteegh

Leeuw

Taricco

et al. 2007

Geochem Geophys Geosyst

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[1] To assess the extent and nature of human-induced climate change, we need to understand natural climate variability. This heavily relies on proxy-based climate reconstructions, calling for excellent understanding of the conditions represented by the proxies. Here we report on an alkenone-based (U 37 K 0 ) sea surface temperature (SST) proxy record originating from south Italian marine sediments, and covering 1305 A.D. to 1979 A.D. with a 3.87 year resolution. The shallow-water cores, extracted from the Gallipoli terrace in the Gulf of Taranto, were dated by the Torino group with high accuracy over the last two millennia, using radiometric and tephroanalysis methods. On the basis of comparison with historical and satellite-derived climate and productivity data, we propose that U 37 K 0 reflects mainly SST of the cooler part of the year and is modified by variation in magnitude and timing of peak alkenone production on the seasonal temperature cycle. Comparison of the U 37 K 0 record with the record of atmospheric D 14 C, a proxy for solar energy variability, shows a high correlation (r = À0.73) for the period between 1420 A.D. and before human interference with the D 14 C record by combustion of fossil carbon and the release of radioactive isotopes by nuclear tests. This suggests a centennial-scale solar forcing. We propose that windinduced mixing resulting from Mediterranean climate dynamics plays a crucial role in translating solar activity to alkenone productivity and SST during the cooler part of the year.

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“…At 300 hpa ( Figure 4) at the same time there is an interaction between the polar and subtropical jet streams southwest of the Atlas Mountains. It may be hypothesised that this interaction causes an increase in the hydrodynamic instability [28] over this region or strengthens the synopticscale upward motion [30], which itself may lead to the development of the vigorous depression L 1 as shown in Figure 1. These views are in need of more research.…”

Section: Analysis and Discussion Of The 27th March 1992 Case Of Coloumentioning

confidence: 99%

“…The suggestion that the interaction of the two jets can initiate and develop the depression due to the increase of hydrodynamic instability which needs more research as Karein [28] based on Defant's theory [29] has studied only one case in the eastern Mediterranean. Also Prezerakos et al [30] have revealed the role of the interaction of these two jets on the rejuvenation of depression over the eastern Mediterranean. The option that these North African depressions can be treated as normal baroclinic waves [27,31,32] associated with the PFJ PV anomalies typically occurring in the winter and the spring due to the approaching of the PFJ over North Africa seems to be more satisfactory.…”

Section: Introductionmentioning

confidence: 98%

Diagnosis of the Relationship between Dust Storms over the Sahara Desert and Dust Deposit or Coloured Rain in the South Balkans

Prezerakos

Παλιατσός

Koukouletsos

2010

Advances in Meteorology

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The main objects of study in this paper are the synoptic scale atmospheric circulation systems associated with the rather frequent phenomenon of coloured rain and the very rare phenomenon of dust or sand deposits from a Saharan sandstorm triggered by a developing strong depression. Analysis of two such cases revealed that two days before the occurrence of the coloured rain or the dust deposits over Greece a sand storm appeared over the north-western Sahara desert. The flow in the entire troposphere is southerly/south-westerly with an upward vertical motion regime. If the atmospheric conditions over Greece favour rain then this rain contains a part of the dust cloud while the rest is drawn away downstream adopting a light yellow colour. In cases where the atmospheric circulation on the route of the dust cloud trajectories is not intensively anticyclonic dust deposits can occur on the surface long far from the region of the dust origin. Such was the case on 4th April, 1988, when significant synoptic-scale subsidence occurred over Italy and towards Greece. The upper air data, in the form of synoptic maps, illustrate in detail the synoptic-scale atmospheric circulations associated with the emission-transport-deposition and confirm the transportation of dust particles.

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The role of the interaction between polar and subtropical jet in a case of depression rejuvenation over the Eastern Mediterranean

Cited by 28 publications

References 20 publications

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Temperature and productivity influences on U₃₇^K′ and their possible relation to solar forcing of the Mediterranean winter

Diagnosis of the Relationship between Dust Storms over the Sahara Desert and Dust Deposit or Coloured Rain in the South Balkans

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The role of the interaction between polar and subtropical jet in a case of depression rejuvenation over the Eastern Mediterranean

Cited by 28 publications

References 20 publications

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

Temperature and productivity influences on U37K′ and their possible relation to solar forcing of the Mediterranean winter

Diagnosis of the Relationship between Dust Storms over the Sahara Desert and Dust Deposit or Coloured Rain in the South Balkans

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Temperature and productivity influences on U₃₇^K′ and their possible relation to solar forcing of the Mediterranean winter