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The predominant climatological wind regime in summer over the Greek Seas and especially over the Aegean Sea is undoubtedly the Etesian winds system, very well known since the time of the ancient Greeks, who first identified and described its main characteristics. The Etesian winds have been under continuous and intensive research since early 1900s, and numerous papers have been published, which have revealed all the secrets associated with the physical mechanisms responsible for their creation and maintenance. The ordinary synoptic situation, which is closely associated with the appearance of spells of Etesian winds outbreaks over the Aegean Sea, refers to cases in which the Subtropical Jet Stream (SJS) is situated over the Greek mainland. Then the frontal surfaces associated with the Polar Jet Stream (PJS), or a polar jet streak, passing through Greece from the north can cause severe weather in northern Greece as far south as Larisa (39.39° N, 22.26° E). Precipitation does not usually occur south of Larisa, because the SJS constitutes a barrier to the southward extension of the upper half of the frontal surface. In this case, cold advection occurs in the lower troposphere, resulting in a drop in temperatures even in southern Greece, due to the establishment of an Etesian winds outbreak. Thereafter, these north-easterly winds persist for a long time, weakening gradually, following the variation of the pressure gradient due to the combination of the mobile dynamic anticyclone positioned over the Balkans, after the passage of the cold front and the permanent Cyprus surface low. The main goal of this article is to investigate how much the case of a time period around 9 July 2022 differs from the conceptual model mentioned above, as deep convection occurred over all of Greece over three successive days, breaking the Etesian winds regime and defeating the low tropospheric stability usually accompanying this wind regime. [ABSTRACT FROM AUTHOR]

Climate variation in temperature describes the fluctuations that occur above or below the average temperature over time. This study focuses on the analysis of various approaches for calculating the average temperature to better capture and represent the true average temperature over the course of a day. As the conventional approach often fails to integrate significant behaviors of temperature variations, nine mathematical formulas are employed with a different number of daily observations. Specifically, this study inserts the geometric and harmonic mean and their variations for the estimation of the average temperature. Furthermore, the application of the formulas to the time series of temperature recordings for three station locations in Greece is analyzed. For the evaluation of the results, six widely used statistical indices for quantifying errors are applied, and their relative effects are also discussed. Finally, as a practical application of the impact of the formula used for the averaging of daily temperature, the various approaches are introduced on the same observation dataset for the estimation of the heating degree-days, an index that can have significant climatological and economic implications over a region. [ABSTRACT FROM AUTHOR]

A network of low-cost sensors operates at six islands in the Aegean Sea (Lemnos, Lesvos, Chios, Samos, Syros and Rhodes) providing real-time PM2.5 concentrations to the public. In the present study, the effect of the prevailing meteorological conditions on the local air quality was examined. For this reason, data about wind direction, dry and wet temperature, wind speed and sunlight were provided by the Hellenic National Meteorological Service for the period from January to September 2022. The analysis of the hourly PM2.5 concentrations revealed different air quality patterns on each island, as well as seasonal changes for the same islands (e.g., higher concentrations in Samos during the cold period). Temperature was found to contribute significantly to the PM2.5 measurements since it affects the anthropogenic activities related to emissions. For instance, higher temperatures in winter result in limited residential heating needs. [ABSTRACT FROM AUTHOR]