Variability of Indian summer monsoon: Relationship with surface air temperature anomalies over northern hemisphere

Thirty year (1950-79) time series of Monsoon Index (MI) is correlated with the gridded surface air temperature data over northern hemisphere land at various time lags of months (i.e., months preceding concurrent and succeeding to the monsoon season) to identify tele-connections of monsoon with the northern hemisphere surface air temperature anomalies. . Out of three key regions identified which show statistically significant relationship of monsoon rainfall, two regions are in the higher latitudinal belt of 40oN- 70oN over North America and Eurasia which show positive correlations with temperatures during northern winter particularly during January and February. The third region is located over northwest India and adjoining Pakistan, where the maximum positive correlation is observed to occur during the pre-li1onsoon months of April and May. These relationships suggest that cooler northern hemisphere during the preceding seasons of winter/spring over certain key regions are generally associated with below normal summer monsoon rainfall over India and vice-versa which could be useful predictors for long-range forecasting of monsoon. There are two large regions in the northern tropics, namely, Asian and African monsoons whose temperatures reveal strong negative correlations with monsoon rainfall during the seasons concurrent and subsequent to the summer monsoon season. However, persistence of this relationship for longer period of about two seasons after the monsoon, suggests the dominant influence of ENSO (El. Nino-Southern Oscillation) on tropical climate.

Brief communication: A ~50 Mm³ ice-rock avalanche on 22 March 2021 in the Sedongpu valley, southeastern Tibetan Plateau

On 22 March 2021, a ~50 M m3 ice-rock avalanche occurred from 6500 m asl in the Sedongpu basin, southeastern Tibet. The avalanche transformed into a highly mobile flow which temporarily blocked the Yarlung Tsangpo river. The avalanche flow lasted ~5 minutes and produced substantial geomorphological reworking. This event, and previous ones from the basin, occurred concurrently with, or shortly after recorded positive air temperature anomalies. The occurrence of future large mass flows from the basin cannot be ruled out, and their impacts must be carefully considered given implications for sustainable hydropower and associated socioeconomic development in the region.

Combined Effects of the British–Baikal Corridor Pattern and the Silk Road Pattern on Eurasian Surface Air Temperatures in Summer

The summer British–Baikal Corridor pattern (BBC) and the Silk Road pattern (SRP) manifest as zonally oriented teleconnections in the high and middle latitudes, respectively, of the Eurasian continent. In this study, we investigate the combined effects of the BBC and SRP on surface air temperatures over the Eurasian continent. It is found that the combination of the BBC and SRP results in two kinds of well-organized, large-scale circulation anomalies: the zonal tripole pattern and the Ω-like pattern in the 200-hPa geopotential height anomalies. The zonal tripole pattern is characterized by opposite variations between western Siberia/western Asia and Europe/central Asia/central Siberia, and the Ω-like pattern manifests as consistent variations over midlatitude Europe, western Siberia, and central Asia. Correspondingly, the resultant large-scale surface air temperature anomalies feature the same zonal tripole pattern and Ω-like pattern, respectively. Further results indicate that these two patterns resemble the two leading modes of surface air temperature anomalies over the middle to high latitudes of Eurasia. This study indicates that the temperature variations in the middle and high latitudes of Eurasia can be coordinated and evidently explained by the combination of the BBC and SRP, and it contributes to a more comprehensive understanding of the large-scale Eurasian climate variability.

Exploring Short-Term Climate Change Effects on Rangelands and Broad-Leaved Forests by Free Satellite Data in Aosta Valley (Northwest Italy)

Satellite remote sensing is a power tool for the long-term monitoring of vegetation. This work, with reference to a regional case study, investigates remote sensing potentialities for describing the annual phenology of rangelands and broad-leaved forests at the landscape level with the aim of detecting eventual effects of climate change in the Alpine region of the Aosta Valley (Northwest (NW) Italy). A first analysis was aimed at estimating phenological metrics (PMs) from satellite images time series and testing the presence of trends along time. A further investigation concerned evapotranspiration from vegetation (ET) and its variation along the years. Additionally, in both the cases the following meteorological patterns were considered: air temperature anomalies, precipitation trends and the timing of yearly seasonal snow melt. The analysis was based on the time series (TS) of different MODIS collections datasets together with Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) collection obtained through Google Earth Engine. Ground weather stations data from the Centro Funzionale VdA ranging from 2000 to 2019 were used. In particular, the MOD13Q1 v.6, MOD16A2 and MOD10A1 v.6 collections were used to derive PMs, ET and snow cover maps. The SRTM (shuttle radar topography mission) DTM (digital terrain model) was also used to describe local topography while the Coordination of Information on the Environment (CORINE) land cover map was adopted to investigate land use classes. Averagely in the area, rangelands and broad-leaved forests showed that the length of season is getting longer, with a general advance of the SOS (start of the season) and a delay in the EOS (end of the season). With reference to ET, significant increasing trends were generally observed. The water requirement from vegetation appeared to have averagely risen about 0.05 Kg·m−2 (about 0.5%) per year in the period 2000–2019, for a total increase of about 1 Kg·m−2 in 20 years (corresponding to a percentage difference in water requirement from vegetation of about 8%). This aspect can be particularly relevant in the bottom of the central valley, where the precipitations have shown a statistically significant decreasing trend in the period 2000–2019 (conversely, no significant variation was found in the whole territory). Additionally, the snowpack timing persistence showed a general reduction trend. PMs and ET and air temperature anomalies, as well as snow cover melting, proved to have significantly changed their values in the last 20 years, with a continuous progressive trend. The results encourage the adoption of remote sensing to monitor climate change effects on alpine vegetation, with particular focus on the relationship between phenology and other abiotic factors permitting an effective technological transfer.

Observational Evidence of Distinguishable Weather Patterns for Three Types of Sudden Stratospheric Warming During Northern Winter

Sudden stratospheric warming (SSW) events often lead to a cold surface air temperature anomaly over the extratropical regions. In this study, we propose, through observational evidence, that the types of SSW determine the severity of the cold anomaly. Based on the three-type classification of SSW, it is found that the surface air temperature drops notably over central to eastern North America following an SSW-type transition, especially from displacement to split. Note, however, that the differences in mean surface air temperature anomalies between SSW types are not statistically significant, even though after SSW-type transition from displacement to split, surface air temperature anomalies are colder than the other two types. The development of an anomalous tropospheric ridge in the North Pacific Arctic sector, associated with the difference in the vertical and zonal propagation of planetary waves, characterizes the post-warming period of the displacement–split type. After the occurrence of the displacement–split type transition of SSW events, upward propagation of planetary waves of zonal wavenumber 1 is suppressed, whereas planetary waves of zonal wavenumber 2 increase in the troposphere. Accompanying the ridge in the North Pacific, a trough developed downstream over North America that carries cold polar air therein. The results in this study are relevant for the subseasonal time scale, within 20 days after an SSW occurrence.

Analysys of the influence of Atlantic-European large-scale atmospheric modes on win-ter anomalies of the surface air temperature in the Black sea-Caspian region

The manifestations of the main large-scale atmospheric processes, typical for the Atlantic–European sector, in winter air temperature anomalies in the Black Sea–Caspian region (40–50 °N 28–50 °E) were clarified according to the atmospheric reanalysis NCEP 20CR V2c data at an isobaric surface of 1000 hPa for 1851–2014. After removing the linear trend, the air temperature anomalies in December-January were decomposed into empirical orthogonal functions (EOF). It is shown that the first three leading EOFs describe ~ 96% of the total air temperature variability. The first EOF is a manifestation of the East Atlantic – Western Russia mode. The second EOF is due to the North Atlantic Oscillation. The third EOF corresponds to the Scandinavian pattern.