Etesian winds after major volcanic eruptions

<p>Etesians winds are northerly winds in the lower atmosphere, blowing over the Aegean basin from early summer to early autumn, regulating summer time heating levels. The interannual variability of Etesians is thought to be linked to the extended Indian Summer Monsoon and tropical Pacific Region. Here, we are investigating the response of Etesians to major volcanic eruptions with the aid of ensembles of historical simulations. Specifically, we are making use of the CESM Last Millennium and Large Ensemble simulations to investigate modelled Etesian changes in the post-eruption one to three years. We find consistent changes for all major eruptions over the last millennium of reduced amplitude peaking in the first year after the eruption. Interestingly, the Laki eruption shows a similar signal to the other major tropical Eruptions. Modelled results are compared to signals in the observational record and a possible mechanism connecting Etesians to the Indian Monsoon region is discussed.</p>

The anomalous low and high temperatures of 2012 over Greece – an explanation from a meteorological and climatological perspective

2012 was the hottest year in Greece on the basis of the available record dating back to 1958, displaying at the same time the widest annual temperature range. During the summer and autumn months, numerous regions in the domain of study experienced record-breaking maximum and minimum temperatures. Conversely, the winter period was particularly cold and January one of the coldest months over the last 55 yr. The analysis of the cold period indicates that the synoptic conditions resemble the positive phase of the Eastern Mediterranean Pattern (EMP). The predominance of these cool conditions seems to be related primarily to an intense NNW or NNE atmospheric circulation, as a consequence of the positive EMP phase. Moreover, the reduction in the floating sea ice emerges as a key driver of the formation of a low-pressure pattern and the reinforcement of the trough south of Scandinavia, which in turn strengthened the Siberia High east of the trough. This reinforcement resulted in a blocking pattern and in favorable conditions for the EMP formation. The atmospheric circulation during the prolonged high-temperature period resembles, respectively, the negative phase of North Sea–Caspian Pattern teleconnection. The observed positive pole, in conjunction with the strong southwestern circulation, results in temperature increases and in the development of a smooth pressure field that contributes to the weakening of the Etesian winds and therefore to calm conditions over the continental areas.

Climatology and Dynamics of the Summer Etesian Winds over the Eastern Mediterranean*

The Etesians are persistent northerly winds that prevail over the eastern Mediterranean during summer. A climatology of Etesian outbreaks over the Aegean was compiled with the aid of the 40-yr ECMWF Re-Analysis (ERA-40) dataset and their vertical organization is investigated. Their variability arises from high-frequency variability originating in the midlatitudes, interannual and intraseasonal variability controlled by the South Asian monsoon, and a local diurnal cycle. Consistent with the monsoon influence, Etesian outbreaks are most frequent from mid-July to mid-August. In agreement with previous studies, a negative trend in the incidence of Etesian outbreaks is detected during the overall June–September period, which is strikingly strong for September but diminishes in June. The strengthening of the Etesians by day over the central and southern Aegean results from the deepening of the Anatolian thermal low because of the daytime sensible heating near the surface. The timing of an outbreak onset is controlled by wave disturbances originating over the North Atlantic that trigger the development of a strong ridge over the Balkans, which induces anomalously strong northerly flow and subsidence over the Aegean. During Etesian outbreaks, sharp tropopause folds and stratospheric intrusions of high potential vorticity descend deeply into the troposphere.

The anomalous low and high temperatures of 2012 over Greece: an explanation from a meteorological and climatological perspective

The year of 2012 is characterized, for Greece, as the hottest one in the available record dating back to 1958, presenting also the widest annual temperature range. During the summer and autumn months, numerous regions in the domain of study experienced record-breaking maximum and minimum temperatures. Conversely, the winter period was particularly cold and January was one of the coldest months in the last 55 yr. The analysis of the cold period indicates that the synoptic conditions resemble the positive phase of the Eastern Mediterranean Pattern (EMP). The predominance of these cool conditions seems to be primarily related to an intense NNW or NNE atmospheric circulation, as a consequence of the positive EMP phase. Moreover, the reduction of the floating sea ice emerged as a key driver to the formation of a low pressure pattern and the reinforcement of the trough south of Scandinavia, which in turn strengthened the Siberia High east of the trough. This reinforcement resulted in a blocking pattern and in the favorable conditions for the EMP formation The atmospheric circulation during the prolonged high-temperature period resembles, respectively, the negative phase of North Sea–Caspian Pattern teleconnection. The observed positive pole, in conjunction with the strong southwestern circulation, results in temperature increases and in the development of a smooth pressure field that contributes to the weakening of the Etesian winds and therefore to calm conditions over the continental areas.