REGIME SHIFTS IN ARCTIC OSCILLATION (AO) VARIABILITY 1951–2009

Arctic Oscillation (AO) reflects the dominating mode of SLP (or 1000hPa) variability in hemispheric scale and seems to bear an effect on the weather and, in longer time scales, on climate. The aim of the research was to identify the possible regime shifts in the multiannual course of AO index which in turn might be utilised in the identification and quantification of the regional/local meteorological field response. The data (AO monthly and daily index values) were acquired from the NOAA Climate Prediction Centre. The AO index is constructed by projecting monthly/daily anomalies of 1000hPa heights poleward of 20°N onto the loading pattern of the AO – 1st (leading) EOF of the 1000hPa height field for the same spatial domain. The temporal scope of analysis was 1951–2009. The analysis comprised the regime shift identification techniques that track the shifts in the mean values and in the magnitude of fluctuations as well as the usage of the classical linear trend identification in the annual and seasonal scale. The regime shift recognition was followed by the compositing method that allowed the analysis of spatial anomalies in SLP field in Euro-Atlantic region that reflect the response of the regional airflow to identified circulation regimes

Variability of geostrophic airflow over Poland, 1951-2014

The paper presents the analysis of the anemological conditions variability over Poland with the usage of geostrophic wind vector as an objective (and homogenous) information concerning the airflow over the area of research. The geostrophic wind vector components are calculated using SLP and air temperature (at sigma995 level) at selected gridpoints which were subsequently interpolated to a central point thus describing the average flow over the research area. The data originated from NCEP/NCAR Reanalysis and its temporal range was 1951-2014. The analysis covers statistical characteristics of the overall annual cycle as well as trend analysis of the airflow features over Poland: geostrophic wind vector module (V), and its zonal (u) and meridional (v) components. Aside from general statistical characteristics for averages and extremes (quantiles 10% & 90%) GEV distribution was fitted to maximum annual/monthly geostrophic wind speed values which allowed the estimation of return levels for selected return periods

Geostrophic wind variability in the 50–60°N zone over Europe: the role of mid-troposphere atmospheric circulation macro-forms

Circulation in the mid-troposphere in moderate and high latitudes of the Northern Hemisphere can be characterised by the Vangenheim-Girs (VG) circulation macro-forms. The aim of the research was to analyse the VG macro-forms as a factor determining the general characteristics of the atmospheric circulation in mid-troposphere in the Euro-Atlantic region and low-troposphere airflow characteristics in the profile (zonal belt) crossing Central Europe from Ireland to Kazan in Russia (5°30’W–44°00’E). Alongside the VG macro-form calendar, ERA-INTERIM data were used. The utilised meteorological variables comprised 500hPa geopotential height, SLP and air temperature at 995 sigma level. The temporal scope of the research was 35 years (1981–2015) and the resolution was 24h (12.00 UTC). The circulation in the low-troposphere was characterised by the geostrophic wind vector characteristics directly resulting from SLP and air temperature fields. Subsequently, derived indices (e.g. wind direction stability) were used. The presented results indicate that the variability of anemological conditions at SLP in the area of 50–60°N over Europe is in direct connection with the mid-troposphere circulation features. The differences are statistically significant across nearly the entire research area. This includes the reversal of the dominant air flow direction in some areas. The greatest variability in geostrophic wind characteristics due to W, E and C VG macro-forms is revealed in the central and eastern part of the 50–60°N zone – between the southern Baltic Sea and the western border of Russia

Regime Shifts in Arctic Oscillation (AO) Variability 1951–2009

Arctic Oscillation (AO) reflects the dominating mode of SLP (or 1000hPa) variability in hemispheric scale and seems to bear an effect on the weather and, in longer time scales, on climate. The aim of the research was to identify the possible regime shifts in the multiannual course of AO index which in turn might be utilised in the identification and quantification of the regional/local meteorological field response. The data (AO monthly and daily index values) were acquired from the NOAA Climate Prediction Centre. The AO index is constructed by projecting monthly/daily anomalies of 1000hPa heights poleward of 20°N onto the loading pattern of the AO – 1st (leading) EOF of the 1000hPa height field for the same spatial domain. The temporal scope of analysis was 1951–2009. The analysis comprised the regime shift identification techniques that track the shifts in the mean values and in the magnitude of fluctuations as well as the usage of the classical linear trend identification in the annual and seasonal scale. The regime shift recognition was followed by the compositing method that allowed the analysis of spatial anomalies in SLP field in Euro-Atlantic region that reflect the response of the regional airflow to identified circulation regimes

Thermal seasons onset and length in Poland – a multiannual perspective on 1971-2010

The major aim of the research is to analyze the variability of thermal seasons characteristics (onset and length), at 7 stations in Poland during the 40-year-long period of 1971–2010. The analysis comprised the selection of the optimal method for season onset identification and the statistical analysis of the season onset and length characteristics, which was augmented with the interdecadal comparison of statistics using one-way analysis of variance (ANOVA). Also, it was investigated if the season onset type (late/normal/early) induces the season length distribution characteristics. The results show that the variability of the onset of thermal seasons is most pronounced in the case of summer and early spring. Summer also shows the tendency to occur faster, whereas autumn tends to start later. The interdecadal change of the thermal seasons length is clearly visible in the case of summer which length systematically increases and winter where the trend is reversed at most of the stations. The research also confirmed that for winter, early spring, and summer, the onset type clearly determines the distribution of the season length. Other seasons either show little variability or the differences appear only at some stations

Downscaling of PDFs of daily air temperature in northern Poland: assessment of predictors

The aim of the research was to validate a set of potential predictors for daily air temperature probability density function (PDF) parameters in northern Poland. The regional forcing comprised SLP (Sea Level Pressure), relative isobaric surface topography, and advection stability coefficients in the Euro-Atlantic region as well as an additional constrained spatial domain (for the air advection stability coefficient). The local response field comprised 24 stations located in northern Poland. The downscaling procedures were carried out in a seasonal framework using monthly values. The local field was described with fitted Gaussian distribution parameters (i.e., tave$t_{ave}$, average; sdt$sd_{t}$, standard deviation) of the daily air temperature. The temporal scope of analysis was 1971 to 2010. Potential regional predictors were assessed, and models were validated, which is important when empirical-statistical downscaling (ESD) models are applied to predict future climate change in terms of the variability in the air temperature PDF parameters

Features of Multiannual Air Temperature Variability in Poland (1951–2021)

Over the last 71 years, the air temperature in Poland has increased on average by 0.28 °C per decade—which gives a total change in this period exceeding 2 °C. The subject of this study was an analysis of the long-term variability of the Polish climate in terms of thermal characteristics. The aim of the research was to verify the hypothesis on the lack of homogeneity of this change and to identify points of significant acceleration of the observed tendencies. The analysis utilized the average monthly air temperature at selected synoptic stations in Poland over the period 1951–2021. The values were then processed into a reference series using Alexandersson’s method, which provided synthetic information on the variability in thermal conditions in the country. The analyses were carried out on an annual and seasonal basis. The values of the trend coefficients (and their statistical significance) were also calculated in shorter periods (minimum 30 years), which enabled determination of the stability of the observed changes’ tendencies. In addition to the analysis of the basic characteristics, non-parametric tests (Wilcoxon, Kruskal–Wallis) were used to verify shifts between decades. The annual and seasonal analyses showed the existence of sub-periods with different directions and scales of the observed tendencies. Additionally, statistically significant changes in decadal characteristics were noted, e.g., in the decades 2001–2010 and 2011–2020 in the case of annual temperature, and 1961–1970 and 1971–1980 in the case of the winter season

The variability of PM₁₀ and PM_2.5 concentrations in selected Polish agglomerations: the role of meteorological conditions, 2006–2016

<p>The research focuses on the analysis of PM₁₀ and PM_2.5 concentrations variability at 11 stations in selected urbanized areas of Poland (Tricity, Poznań, Łódź, Kraków). Methods comprised: the analysis of basic statistical characteristics in yearly/monthly/daily/hourly scale and threshold exceedance frequencies. Also, correlations between PM₁₀ and meteorological variables were investigated. GEV distribution analysis allowed the estimation of the return levels of monthly maxima of PM₁₀ and PM_2.5. Results show that in Tricity there are fewer than 5 % of days with PM₁₀ and PM_2.5 threshold exceedance. In Kraków, the standards are only met during summer and the frequency of daily PM limit exceedance in winter was around 65–90 %. GEV analysis indicates that 10<i>y</i> return level of PM₁₀ monthly maximum daily average do not usually exceed 250 μg/m³ at most of the stations (Kraków agglomeration is an exception here). In winter, the meteorological conditions unfavourable to the pollutant’s dispersion comprise: high-pressure systems, stable equilibrium in the atmosphere and limited turbulence occur quite often together with low wind speed and reduced height of the planetary boundary layer.</p