The forecast of extreme weather events become imperative due to the emerging climate change and possible adverse effects in humans. The objective of this study is to construct predictive models in order to forecast rain intensity (mm/day) in Athens, Greece, using Artificial Neural Networks (ANN) models. The ANNs outcomes concern the projected mean, maximum and minimum monthly rain intensity for the next four consecutive months in Athens. The meteorological data used to estimate the rain intensity, were the monthly rain totals (mm) and the respective rain days, which were acquired from the National Observatory of Athens, for a 111-year period (1899–2009). The results of the developed and applied ANN models showed a fairly reliable forecast of the rain intensity for the next four months. For the evaluation of the results and the ability of the developed prognostic models, appropriate statistical indices were taken into consideration. In general, the predicted rain intensity compared with the corresponding observed one seemed to be in a very good agreement at a statistical significance level of p

Rain intensity forecast using Artificial Neural Networks in Athens, Greece

The agricultural sector in Poland is of considerable social and economic importance for the nation. Climate variability and change are of primary relevance to this largely climate-dependent sector. Changes in seven temperature-related agroclimatic indices (lengths of the growing season and of the frost-free season, days of occurrence of the last spring frost and of the first autumn frost; and annual sums of growing degree-days for three values of temperature threshold) in Poland in 1951–2010 are examined. As expected, they generally correspond to the overwhelming and ubiquitous warming. Many, but not all, detected trends are statistically significant. However, for some indices, strong natural variability overshadows eventual trends. Projections of temperature-related agroclimatic indices for the future, based on regional climate models, are also discussed.

/pdf/changes-of-temperature-related-agroclimatic-indices-in-3y25ui44ec.pdf

Changes of temperature-related agroclimatic indices in Poland

Dendrochronological research in North-Central Europe and the East Mediterranean has produced networks of long regional oak (Quercus sp.) reference chronologies that have been instrumental in dating, provenancing, and paleoclimate research applications. However, until now these two important tree-ring networks have not been successfully linked. Oak forests and historical/archaeological sites in southeastern Europe provide the key for linking the North-Central European and East Mediterra- nean tree-ring networks, but previous dendrochronological research in this region has been largely absent. This article presents the initial results of a project, in which we have built oak tree-ring chronologies from forest sites and historical/archaeological sites along a north-south transect between Poland and northwestern Turkey, with the aim of linking the North-Central European and East Mediterranean tree-ring networks and creating a new pan-European oak data set for dendrochronological dating and paleoclimatic reconstruction. Correlation among tree-ring chronologies and the spatial distribution of their teleconnections are evaluated. The southeastern European chronologies provide a solid bridge between both major European dendrochronological networks. The results indicate that a dense network of chronologies is the key for bridging spatial and temporal gaps in tree-ring records. Dendrochronological sampling should be intensively continued in southeastern Europe because resources for building long oak chronologies in the region are rapidly disappearing.

https://dendro.cornell.edu/articles/Waznyetal.2014.pdf

Bridging the Gaps in Tree-Ring Records: Creating a High-Resolution Dendrochronological Network for Southeastern Europe

Research on relationships between large scale atmospheric circulation and different climatic and environmental variables has multiplied, and with it the need for a simple description of atmospheric conditions. This has led to renewed interest for weather and circulation type classifications. The objective of cost Action 733 was to develop a classification technique scalable to any European region for a wide range of applications. A necessity to reach this goal was to develop a general numerical approach for assessing and comparing classifications of atmospheric circulation and typical weather situations in European regions. In addition, the action aimed to increase the knowledge of the relationships between atmospheric circulation and responding weather, climate and environmental variables. During five years the Action succeeded to produce an extensive, consistent catalogue of atmospheric circulation type classifications (cost733cat) based on different methodological concepts. The resulting catalogue and associated classification types are produced through an open source (GPL) software developed within the Action (cost733class), allowing to generate classifications from a wide number of algorithms and parameter options. Hence it provides a freedom to generate classifications tailored to any location or potential application. Criteria and procedures to systematically evaluate circulation type classifications are defined and tested, and several of these are included in the software. The Action has provided a unique opportunity to systematically evaluate an extensive number of classifications within a coordinated inter-disciplinary environment, and has increased the knowledge on a range of classification approaches, extremely useful for developing any new weather type classification method for European Regions.

COST Action 733. Harmonization and application of weather type classifications for European regions. Final scientific report

Long-term precipitation variability on thunderstorm days in Poland (1951–2000)

The paper proposes a classification of deep cyclones determining the weather in Poland grouped according to their track. The study used data from NCEP/NCAR reanalysis spanning the period 1971–2000. The analysis considered: values of 1000 hPa geopotential height at 12 UTC recorded at selected grid points, maps of 1000 and 500 hPa geopotential height and maps of sea-level air-pressure field at 12 UTC. Seven groups of deep cyclones were identified. The dominant groups involved cyclones originating over the North Atlantic and crossing over Iceland (T2 = 29.3%), and those moving from west to east, typically over the British Isles (T3 = 26.8%). Other large groups of cyclones involved systems travelling from the Mediterranean towards north-eastern Europe (T7 = 10.5%), and those moving from the Norwegian Sea though the Baltic Sea into northern and north-eastern Europe (T1 = 8.4%). Cyclones, with air pressure ranging from 940 to 1000 hPa, were found to have different levels of influence depending on the region. Most of the systems were recorded between October and March (86.4%), but isolated cases were also observed in summer. No statistically significant long-term trends in their occurrence were identified.

A classification of deep cyclones over Poland (1971–2000)

Wieloletnia zmienność okresu bezprzymrozkowego w Polsce w latach 1951–2006

The paper presents a classification of weather types observed in Krakow during the 20th century on days with particularly strong highs. The classification was based on daily values of a number of weather elements recorded at Krakow's Historic Weather Station during the period 1901–2000. Days with very high pressure were defined as those with an air pressure at 12 UTC equal to or greater than the 99th percentile of all the cases analysed (≥1037.5 hPa). A slightly modified version of a classification developed by Woś (1999) was used to determine weather types on each of the days identified. Very high pressure was found to have occurred solely during the cold half of the year (October–March). It was mostly accompanied by fairly frosty (9---) or moderately frosty (8---) weather types; subtype: sunny or with little cloud amount and very sunny (-02-) and very cloudy, without sunshine or with little sunshine (-20-); and weather class: without fog (---0). No significant annual or seasonal trends were found in the occurrence of days with very high pressure or in the various weather types. Copyright © 2010 Royal Meteorological Society

Weather types accompanying very high pressure in Krakow in the period 1901–2000

This study determines the frequency, location and spatial extent of such large-area monthly thermal anomalies, which are referred to in this paper as continental-scale thermal anomalies (CTAs). The research was based on monthly mean air temperature values from 210 weather stations over the 68-year period 1951-2018. A CTA is defined as an anomaly when the monthly mean temperature exceeded the long-term average by at least 2 standard deviations at a minimum of 40 stations. This study attempts to explain the occurrence of such CTAs (negative CTAs- and positive CTAs+) in relation to the circulation conditions over Europe. In the years 1951-2018, there were 16 CTAs- (mainly in winter and autumn) and 25 CTAs+ (predominantly in summer). One manifestation of climate warming is the ever less frequent occurrence of CTAs- and a growing frequency and spatial extent of CTAs+. The immediate cause behind CTAs was the occurrence of characteristic synoptic situations, leading to intensified advection of cold or hot air masses, often driven by radiation factors. The formation of CTAs- was much more often associated with very extensive and long-lasting anticyclonic systems, and that the associated synoptic situations over Europe lasted much longer than in the case of CTAs+.

http://rcin.org.pl/igipz/Content/234341/WA51_271568_r2022-t95-no1_G-Polonica-Twardosz.pdf

Zuzanna Bielec-Bakowska

Papers

Long-term precipitation variability on thunderstorm days in Poland (1951–2000)

A classification of deep cyclones over Poland (1971–2000)

Wieloletnia zmienność okresu bezprzymrozkowego w Polsce w latach 1951–2006

Weather types accompanying very high pressure in Krakow in the period 1901–2000

Continental-scale monthly thermal anomalies in Europe during the years 1951-2018 and their occurrence in relation to atmospheric circulation