Preferred intra-seasonal circulation patterns of the Indian summer monsoon and active-break cycles

Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean anomaly fields of 850 hPa horizontal winds from the ERA-Interim reanalysis for the boreal summer season (June–Sept. for 1979–2018) over the region (50°–100° E; 5° S–35° N). The k-means method was applied to the leading 6 principal components yielding k clusters. The degree of clustering is significant compared to synthetic data sets for any value of $$k > 3$$ k > 3 . The circulation is most likely to stay in the same cluster from one pentad to the next; significant transitions (with 95% confidence level) form a cycle. The similarity between the cycle depicted from 4 or 5 clusters and the active-break cycle, as well as the 45-day oscillation, is established by composites of 850 hPa winds, 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, precipitable water, diabatic heating and rainfall over India: Strong convection over the subtropical Indian Ocean moves to the central Bay of Bengal and central India, subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. We also find preferred transitions in which the convection moves equatorward from central India. The number of complete cycles found in 40 summers is 7 in the 4-cluster analysis. The number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). For 5 clusters only 3 complete cycles are found. sequences of five, four and three consecutive legs occur 10, 11 and 28 times, respectively.

Interconnection between the Southern South China Sea and the Java Sea through the Karimata Strait

This study aims to investigate the interconnection between the southern South China Sea (SSCS) and Java Sea (JS) by simulating seasonal circulations and associated transports using the Regional Ocean Modelling System (ROMS). The seasonal circulation was predominantly driven by monsoonal wind stress and water exchanges between the SSCS and the JS. During the boreal winter, cooler and saltier waters from the SSCS were advected into the JS, while during the boreal summer, cooler waters from the JS were advected into the SSCS, with the advection of fresher water onto the Peninsular Malaysia’s east coast in the SSCS being the new finding provided by this study. The various water transports were driven southward into the JS during the boreal winter and northward into the SSCS during the boreal summer. The various water transports estimated by ROMS peaked in May during the inflow months from the JS into the SSCS, which was attributed to the simulated anticyclonic eddy in the SSCS, which differed from previous studies that peaked between June and August. The annual mean volume, freshwater, heat, and salt transports were 0.96 Sv, 0.04 Sv, 0.10 PW, and 0.03 × 109 kg s−1, respectively, directed from the SSCS into the JS.

Preferred Intra-seasonal Circulation Patterns of the Indian Summer Monsoon and Active-Break Cycles

Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean (pentad) anomaly fields of 850 hPa horizontal winds (u,v)from the ERA-Interim reanalysis for the boreal summer season (120 days starting 01June for the years 1979 - 2018) over the broad Indian region (50 o -100 o E; 5 o S - 35 o N). The anomalies are formed with respect to a parabolic (in time) seasonal cycle computed separately for each year, thus filtering out periods of greater than 240 days. The k-means method was applied in the phase space of the leading 6 (12) principal component modes, which explain 65% (78%) of the space-time variance, yielding k clusters. The degree of clustering is significant when compared to synthetic data sets for any value of k > 3. The transition matrices for k=4 and k=5 establish that the system is most likely to stay in the same cluster from one pentad to the next, but that the significant transitions (with 95% confidence level using a modified bootstrap method) form a cycle. The similarity between the cycle as depicted from 4 or 5 clusters is established by composites of 850 hPa (u,v,), 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, and daily rainfall over India: Strong convection (with large positive divergence and vorticity) over the subtropical Indian Ocean, moves to the central Bay of Bengal and over central India, then subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. The Indian rainfall composites show a similar cycle. The phases in which strong convection is seen over central and northern India are seen for about 60% of the time for both k=4 and k=5 analyses. However the 4 cluster analysis also shows a preferred transition in which the convection moves equatorward from central India. The number of complete cycles (including a return to the starting cluster) found in the 40 years of data is 7 in the 4-cluster analysis, while the number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). Fewer instances of complete cycles are found for 5 clusters (only 3), but sequences of five, four and three consecutive legs occur 10, 11 and 28 times respectively. Composites of the tropics-wide vertically integrated diabatic heating (estimated from ERA5 reanalyses) reproduce the characteristics of the boreal summer intra-seasonal oscillation, with northwest-to-southeast oriented bands of heating moving northward from the tropical Indian Ocean into the subtropics. This depiction of the active-break cycle is particularly useful for diagnosing the cycle in short-range forecasts: as long as pentad anomalies can be formed, they can be assigned to one of the observed clusters described in this paper without the need for further time-filtering.

Improvement of Odin/SMR water vapour and temperature measurements and validation of the obtained data sets

Its long photochemical lifetime makes H2O a good tracer for mesospheric dynamics. Temperature is also an important tracer of seasonal circulation as well as multi-year trends. In this study we present the reprocessing of 18 years of mesospheric H2O and temperature measurements from the Sub-Millimetre Radiometer (SMR) on board the Odin satellite, resulting in a part of the SMR version 3.0 level 2 data set. The previous version of the dataset showed poor accordance with measurements from other instruments, which suggested that the retrieved concentrations and temperature were subject to instrumental artifacts. Different hypotheses have been explored, and the idea of an underestimation of the single sideband leakage turned out to be the most reasonable one. The value of the lowest transmission achievable has therefore been raised to account for greater sideband leakage, and new retrievals have been performed with the new settings. The retrieved profiles extend between 40–100 km altitude and cover the whole globe to reach 85° latitudes. A validation study has been carried out, revealing an overall better accordance with the compared instruments. In particular, relative differences in H2O concentration are always in the ±20 % range between 40 and 70 km and diverge at higher altitudes, while temperature absolute differences are within ± 5 K between 40–80 km (with the exception of FM13 SMR–MLS difference reaching almost 10 K) and also diverge at higher altitudes.

THE IMPACT OF SEASONAL CHANGES ON HEAVY MINERALS CONCENTRATION FROM A PART OF EAST COAST OF INDIA

Pre and post monsoonal changes in the environment have led to a noticeable variation in sediment characteristics, heavy mineral concentrations and their distribution. The current study aimed to find out the effect of seasonal fluctuations on the concentration of heavy minerals along the coast and the variations in sediment textures and distribution. The study has revealed the effect of seasons on the sediments supply and its distribution along coast in the study area. The total heavy minerals concentrations are more in post monsoon than in pre monsoon and the concentration also increases from south to north in parts of the study area because of seasonal circulation of currents from south to north along the shore. The micro textural study of the heavy mineral grains from different locations in the study area revealed the mechanical and chemical erosions on the grain surfaces.

Autochthonous West Nile virus infection outbreak in humans, Leipzig, Germany, August to September 2020

Following a distinct summer heat wave, nine autochthonous cases of West Nile fever and West Nile neuroinvasive disease, including one fatality, were observed in Leipzig, Germany, in August and September 2020. Phylogenetic analysis demonstrated close relationships in viruses from humans, animals and mosquitos in eastern Germany, obtained during the preceding 2 years. The described large cluster of autochthonous West Nile virus infections in Germany indicates endemic seasonal circulation of lineage 2 viruses in the area.