The Impact of the East Atlantic/Western Russia Pattern on the Hydroclimatology of Europe from Mid-Winter to Late Spring

Monica Ionita
2014 Climate  
In this study, the influence of the East Atlantic/Western Russia teleconnection pattern on the hydroclimatology of Europe, from mid-winter to late spring, is investigated. The influence of EAWR on the variability of precipitation (PP), temperature (TT) and standardized precipitation-evapotranspiration index (SPEI) is investigated on the base of correlation and stability maps. It is shown that EAWR has a strong impact on the coupling between the sub-tropical Atlantic Jet and the African Jet,
more » ... he African Jet, which in turn affects the climate variability over Europe from mid-winter to late spring. The strongest impact of the mid-winter EAWR over the European precipitation is found to be in mid-winter and early spring over the northern part of the Scandinavian Peninsula and the central and eastern part of Europe; while the influence of the mid-winter EAWR on European temperature persists from mid-winter to late spring, giving the possibility of a potential predictability for spring temperature over extended European regions. 297 of phase, owing to the action of such teleconnections, which modulate the location and strength of the storm tracks and poleward fluxes of heat, moisture and momentum [3] [4] [5] . Such monthly, seasonal and longer-time scales anomalies have direct impacts on humans, as they are often associated with floods, droughts, heat or cold waves and other factors that can directly affect and disrupt agriculture, water supplies, and can modulate the fresh water quality, energy demands and human health. The strength of these teleconnections and the way they influence surface climate variables varies over long time scales [1] [2] [3] . The climate over the European region is dominated by the North Atlantic Oscillation (NAO) [3, 6] . NAO is the leading mode of climate variability in the North Atlantic region and is characterized by a meridional seesaw in the atmospheric pressure between the Icelandic Low and the Azores High. Periods with positive values of the NAO index are characterized by an enhanced westerly flow across the North Atlantic and the European region and higher than normal surface pressure south of 55°N combined with a broad region of anomalously low pressure throughout the Arctic and subarctic. Consequently, this phase is associated with stronger-than-average winds across the mid-latitudes of the Atlantic onto Europe, with anomalously southerly flow over the eastern United States and anomalously northerly flows across Greenland, the northern part of Canada and the Mediterranean region and enhanced easterly trade winds over the sub-tropical North Atlantic [7] . Although NAO is one of the most prominent teleconnection patterns in all seasons [2], its relative role in regulating the variability of the European climate during non-winter months is not as clear as for the winter season. At the same time, the mechanisms which drive the European climate variability might vary from one climatic period to another and also might be different for different variables (e.g., precipitation, streamflow, air temperature). Another prominent teleconnections pattern over the North Atlantic region is the East Atlantic-West Russia (EAWR). The EAWR was originally identified through an orthogonally rotated principal component analysis (RPCA) applied to the monthly-mean geopotential height at 700 hPa and consists of four main anomaly centers [2] . The positive phase is associated with positive height anomalies located over Europe and northern China, and negative height anomalies located over the central North Atlantic and north of the Caspian Sea. During the positive (negative) phase of the EAWR, wetter (drier) conditions are observed over eastern China and drier (wetter) conditions prevail across central Europe and the Mediterranean Region. The positive (negative) phase of EAWR is also associated with above-average (below-average) temperatures over eastern Asia and below-average (above-average) temperatures over western Russia and northeastern Africa [2] . EAWR was found to have a strong influence over the precipitation in the Mediterranean region [8, 9] . According to the aforementioned studies, extreme wet (dry) winter months over the Mediterranean region were characterized by anomaly patterns which project onto the negative (positive) phase of EAWR. A strong relationship between EAWR and the temperature variability inside a cave from the north-western part of Romania has also been found [10] . High (low) temperatures inside the cave are associated with an atmospheric circulation that resembles the center of action of the EAWR pattern [11] found that both NAO as well as EAWR play a significant role on the variability of cyclones and wind activity over the Mediterranean region. According to the aforementioned study, during the positive phase of EAWR, the storm numbers over the central Mediterranean region are decreasing and the number of strong wind events over the eastern Mediterranean region is increasing.
doi:10.3390/cli2040296 fatcat:3dpthhljqnf73j4hriwnguiyxi