Vol. 129, No. 1 * Pages 1–105 * January - March 2025

This research aims to evaluate a quantitative comparison of the visibilities detected by three different methods: (i) human eye-based observations; (ii) calculated from the measured values of forward scatter visibility sensor; and (iii) evaluated from ceilometer’s vertical backscattering profiles. Visibility data observed at two meteorological stations, Pestszentlőrinc and Szeged (Hungary) were analyzed. The paper focuses on the fog events observed during the periods of October-December in 2019 and November 21-24 in 2020. The results reveal that the visibility observed by the three methods can be significantly different. Comparison of the values of visibility detected by the three different techniques shows, that visibility evaluated from the ceilometer data is the largest, and the human eye-based observation detects the smallest values. Analysis of the data about fog detection (yes or no) reveals that the ceilometer detects significantly shorter duration of the fog than the other two methods.

In this study, a temporal analysis of lightning density was performed on lightning data obtained from the Türkiye State Meteorological Service (TSMS) for the period 2017–2021, with the analysis encompassing hourly, monthly, seasonal, and annual scales. ArcGIS version 10.4.1 was used. When the annual lightning density was evaluated by regions, the highest values were observed in the Inner Aegean, Marmara, Southwest Anatolia, Western Black Sea, and Eastern Anatolia Regions. The Central Anatolia Region has the lowest lightning density. Lightning density is also the highest in late spring, early summer when the ground temperature and, thus, instability is highest. May and June were determined to have the highest lightning density, whereas December, January, and February had the lowest lightning density. Considering lightning activity hourly, the highest number of lightning strikes occurred at noon, while the lowest number occurred at night and during the morning hours. Upon examining the relationship of lightning with latitude and longitude values, it was concluded that the relationship with latitude values was more significant and positive. Lightning changes as a function of altitude: it increases between 30-150 m and 500-1000 m, while it decreases between 150-500 m and above 1000 m.

In general, there would be one monsoon depression affecting the South China Sea every summer. Such depressions are relatively short-lived and mostly last for a few days. In early June 2023, there was a relatively long-lived monsoon depression over the South China Sea with a lifespan of around 10 days. The paper documents the life of this monsoon depression, including the meteorological observations. This depression is found to have the typical structure of a monsoon depression, namely, very weak winds near the center and higher wind speed with intense convection associated with a burst of southwest monsoon in its periphery. The strong southwest monsoon was also observed as a boundary layer jet in the upper air observations. The study is unique from the perspective that there are more meteorological observations over the northern part of the South China Sea, including the weather buoys and oil platforms, which provide unprecedented meteorological observations of the depression. It is hoped that this paper could stimulate further studies of monsoon depressions in this region in the future.

Within the scope of the global climate change, monitoring and assessment of meteorological parameters gain growing importance. Hence, the analysis of long-term climate series having either increasing or decreasing trend, makes relevance to the weather patterns, and often provides further prediction of extreme meteorological events in the near future.
In this perspective, this research purposes to investigate and interpret temperature and rainfall trends as well as the effect of climate change in three main districts from the Setifian High Plains region, namely, Setif, Ain Oulmene, and Boutaleb. Meteorological data were extracted from the TerraClimate dataset available at the Google Earth Engine platform over a 42-year-long period (from 1980 to 2021). Mann-Kendall, Spearman’s rho, and Şen’s trend tests were used to assess the trend, while Pettitt’s test was applied to detect the change point in time series data. The Theil-Sen approach was used to estimate the slope magnitude in the series. Results showed significant increasing trends in the minimum, maximum, and average temperatures over time for all the three stations. The magnitude of the upward trend in temperature data was found to be at the rate of 0.023 to 0.03 °C per year for all stations. Pettitt’s test found the year 1998 as a change point both for the maximum and average annual temperatures for all stations, while the year 2013 was detected as a change point in the minimum temperature for Ain Oulmene and Boutaleb stations. However, rainfall showed non-significant decreasing trends at 5% significance level for all stations.
This study concludes that there is an increase in climate variability over the sampling period, which reveal the necessity of adopting the suitable adaptation strategies for facing the impact of climate change.

Water quantity is often analyzed throughout mean annual and seasonal discharges in various studies worldwide. This paper aims to present water discharge trends in the lower parts of the Una, Sana, and Vrbanja rivers in Bosnia and Herzegovina and the largest Serbian national river Velika Morava and its tributaries Jasenica and Resava rivers in Serbia for the period 1961–2020. Also, the paper examines air temperature and precipitation trends and their connection with discharge trends. Mann-Kendall test was applied for the determination of trends in air temperature, precipitation, and discharges; the Sen's nonparametric estimator was utilized for establishing the magnitude of the trend, while the t-test was used for determining the statistical significance of the trend. In order to determine possible changes, two periods were observed: 1961–1990 and 1991–2020. Results showed statistically insignificant changes in discharges and precipitation trends on annual and seasonal levels. On the other hand, a significant air temperature increase was recorded in the period 1991–2020, with the highest increase during the summer. The most significant increase was observed in Banja Luka due to urban heat island effect in this city.

Recent years have seen a marked increase in the number of disasters caused by the effects of global climate change. In response, a range of studies have been conducted in Türkiye and worldwide with the aim of reducing the impact of climate change.The classification of regions affected by climate change into similar classes in terms of climate parameters is crucial for the application of consistent methods in studies conducted in these regions. Consequently, the formulation of effective strategies to mitigate the repercussions of climate change in these regions is contingent upon the accurate determination of the aforementioned strategy. The observation records evaluated within the scope of the study were obtained from 31 stations of the Turkish State Meteorological Service in the Black Sea Region, encompassing the period between 1982 and 2020, encompassing precipitation, temperature, and wind speed records.. The maximum number of clusters was determined as 5, the cluster analysis study was carried out by using fuzzy c-means and k-means methods for 2, 3, 4, and 5 cluster numbers according to these three data together form a matrix. The determination of the optimum cluster numbers was carried out by silhouette index analysis. For the data matrix where precipitation, temperature, and wind speed were evaluated together, the most appropriate classification was obtained by the k-means method by choosing the number of clusters as 4.