A scheme for advance prediction of northeast monsoon rainfall of Tamil Nadu

Monthly means of winds. contour height and temperature of seven standard isobaric levels of ten well distributed Indian upper air stations for the months of April, June. July, August and September were subjected to correlation analysis to detect parameters that have predictive value to forecast in advance the northeast monsoon rainfall of Tamil Nadu. The period 1965-87 was taken as developmental period and 1988-94 as test period. Six predictors, out of which three were completely new, were identified. The final forecast of rainfall was obtained as the weighted average of the individual forecasts based on the six predictors by employing a screening technique different from the conventional ones. The system explained between 65-77% variation of the predict and with standard error of 13-18% and provided reasonably correct forecasts during the test period. The physical significance of the predictors has been explained based on the intensity of the subtropical anticyclone over India. The possibility of extending the study to include global parameters in the context of proven negative and significant relationship between Southern Oscillation Index (SOl) and the Indian northeast monsoon has been discussed. Scope for further studies on the topic has been spelt out.

The influence of direct radiative forcing versus indirect sea surface temperature warming on southern hemisphere subtropical anticyclones under global warming

Southern hemisphere subtropical anticyclones are projected to change in a warmer climate during both austral summer and winter. A recent study of CMIP 5 & 6 projections found a combination of local diabatic heating changes and static-stability-induced changes in baroclinic eddy growth as the dominant drivers. Yet the underlying mechanisms forcing these changes still remain uninvestigated. This study aims to enhance our mechanistic understanding of what drives these Southern Hemisphere anticyclones changes during both seasons. Using an AGCM, we decompose the response to CO2-induced warming into two components: (1) the fast atmospheric response to direct CO2 radiative forcing, and (2) the slow atmospheric response due to indirect sea surface temperature warming. Additionally, we isolate the influence of tropical diabatic heating with AGCM added heating experiments. As a complement to our numerical AGCM experiments, we analyze the Atmospheric and Cloud Feedback Model Intercomparison Project experiments. Results from sensitivity experiments show that slow subtropical sea surface temperature warming primarily forces the projected changes in subtropical anticyclones through baroclinicity change. Fast CO2 atmospheric radiative forcing on the other hand plays a secondary role, with the most notable exception being the South Atlantic subtropical anticyclone in austral winter, where it opposes the forcing by sea surface temperature changes resulting in a muted net response. Lastly, we find that tropical diabatic heating changes only significantly influence Southern Hemisphere subtropical anticyclone changes through tropospheric wind shear changes during austral winter.

The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence

Highly unusual amounts of rainfall were seen in the 2020 summer in many parts of China, Japan, and South Korea. At the intercontinental scale, case studies have attributed this exceptional event to a displacement of the climatological western North Pacific subtropical anticyclone, potentially associated Indian Ocean sea surface temperature patterns and a mid-latitude wave train emanating from the North Atlantic. Using clusters of spatial patterns of sea level pressure, we show that an unprecedented 80% of the 2020 summer days in East Asia were dominated by clusters of surface pressure greater than normal over the South China Sea. By examining the rainfall and water vapor fluxes in other years when these clusters were also prevalent, we find that the frequency of these types of clusters was likely to have been largely responsible for the unusual rainfall of 2020. From two ensembles of future climate projections, we show that summers like 2020 in East Asia may become more frequent and considerably wetter in a warmer world with an enhanced moisture supply.

High-Frequency Variability of the Surface Ocean Properties Off Central Chile During the Upwelling Season

The ocean off south-central Chile is subject to seasonal upwelling whose intensity is mainly controlled by the latitudinal migration of the southeast Pacific subtropical anticyclone. During austral spring and summer, the mean flow is equatorward favoring coastal upwelling, but periods of strong southerly winds are intermixed with periods of relaxed southerlies or weak northerly winds (downwelling favorable). This sub-seasonal, high-frequency variability of the coastal winds results in pronounced changes in oceanographic conditions and air-sea heat and gas exchanges, whose quantitative description has been limited by the lack of in-situ monitoring. In this study, high frequency fluctuations of meteorological, oceanographic and biogeochemical near surface variables were analyzed during two consecutive upwelling seasons (2016–17 and 2017–18) using observations from a coastal buoy located in the continental shelf off south-central Chile (36.4°S, 73°W), ∼10 km off the coast. The radiative-driven diel cycle is noticeable in meteorological variables but less pronounced for oceanographic and biogeochemical variables [ocean temperature, nitrate (NO3−), partial pressure of carbon dioxide (pCO2sea), pH, dissolved oxygen (DO)]. Fluorescence, as a proxy of chlorophyll-a, showed diel variations more controlled by biological processes. In the synoptic scale, 23 active upwelling events (strong southerlies, lasting between 2 and 15 days, 6 days in average) were identified, alternated with periods of relaxed southerlies of shorter duration (4.5 days in average). Upwelling events were related to the development of an atmospheric low-level coastal jet in response to an intense along-shore pressure gradient. Physical and biogeochemical surface seawater properties responded to upwelling favorable wind stress with approximately a 12-h lag. During upwelling events, SST, DO and pH decrease, while NO3−, pCO2sea, and air-sea fluxes increases. During the relaxed southerly wind periods, opposite tendencies were observed. The fluorescence response to wind variations is complex and diverse, but in many cases there was a reduction in the phytoplankton biomass during the upwelling events followed by higher values during wind relaxations. The sub-seasonal variability of the coastal ocean characterized here is important for biogeochemical and productivity studies.

Estudo da atuação do anticiclone subtropical do Atlântico Sul sobre a umidade relativa do ar no entorno do Parque Estadual do Rio Doce por meio de revisão sistêmica da literatura

O objetivo deste artigo foi realizar levantamentos na literatura em estudos sobre o Anticiclone Subtropical do Atlântico Sul e suas características relacionadas à umidade relativa do ar. O levantamento foi baseado no método de revisão bibliográfica sistemática. A pesquisa foi realizada por meio de consulta nas bases de dados: Google Acadêmico, Capes e Scielo. Verificamos que o tema “Anticiclone Subtropical do Atlântico Sul (ASAS)” é bastante discutido na literatura, tanto em relação aos mecanismos de formação dos sistemas de alta pressão quanto à sua influência sobre as condições meteorológicas. Alguns trabalhos abordaram temas referentes aos impactos advindos da presença deste sistema atmosférico e às questões socioambientais, notando-se, ainda, uma pequena quantidade de artigos e trabalhos que abordam ações preventivas que devem ser inseridas em épocas de ocorrência do ASAS. Palavras-chave: Influência do ASAS. Sistema de alta pressão. Dinâmica atmosférica. Study of the action of the subtropical anticyclone of the South Atlantic on the relative air humidity in the surroundings of the Rio Doce State Park, through a systematic literature review AbstractThe objective of this article was to carry out surveys in the literature in studies on the South Atlantic Subtropical Anticyclone and its characteristics related to the relative humidity of the air. The survey was based on the systematic bibliographic review method. The research was carried out by consulting the databases: Google Acadêmico, Capes and Scielo. We found that the theme "South Atlantic Subtropical Anticyclone - ASAS" is widely discussed in the literature, both in the mechanisms of formation of high-pressure systems and their influence on weather conditions. Some works addressed issues related to the impacts arising from the presence of this atmospheric system and socioenvironmental issues. Still there is also a smallnumber of articles and works that address preventive actions in which they should be inserted in times of occurrence of ASAS. Keywords: Influence of ASAS. High Pressure System. Atmospheric dynamics.

Climate Change and the Evolution of Phytoplankton (Abundance) in Some Lagoons on the São Miguel Island – Azores

<p>Climate change cause large, long-term impacts on human well-being and adds more pressure to terrestrial and marine ecosystems. The archipelago of the Azores is located in the subtropical region of the North Atlantic and is therefore highly influenced by the North Atlantic Subtropical Anticyclone. As it is an almost stationary high pressure system, whose development and orientation determine the nature and characteristics of the air masses that reach the region. The motivation for this research has two phases; the first was to study the effects of some meteorological parameters (temperature, radiation, wind speed, humidity, precipitation, evaporation, tank temperature and tank level) for the period 2010-2012, on the biodiversity of phytoplankton communities in relation to the abundance of these organisms in the lagoons of Fogo, Furnas, and Sete Cidades of the island of São Miguel - Azores, for the period 2010-2012, using an analysis in Principal  Components, which will allow correlating the meteorological parameters and the abundance of phytoplankton. The phytoplankton and meteorological community data were obtained from the website of the Regional Secretariat for the Environment and Climate Change of the Azores Government. In a second phase, the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis of the ERA5 project (ECMWF Re-Analyzes) was used for the 1979-2019 observation period and for the Azores region. For this region, the deviations of the surface air temperature, average annual precipitation and climatological extremes were calculated, this referring to the maximum number of consecutive days with precipitation <1 mm, and also, the number of tropical nights using the ERA5 reanalysis series in the period 1979-2019 with reference to 1961-1990. Projections were also estimated up to 2100 and according to scenarios RCP 2.6, 4.5 and 8.5 for the referred parameters. Finally, variations for the end of the century (2071-2100) were estimated with reference to the most recent situation of 1991-2020.</p><p>The thermal balance of a lagoon is associated with climatic and meteorological conditions. Much of the biological processes in the lagoons are directly affected by thermal changes in the water, and therefore, indirectly affected by climatic variation. Understanding the interaction between the lagoon-atmosphere system is important to predict the consequences of the effects of climate change on the abundance of phytoplankton. In this study, a positive correlation was verified between precipitation and abundance of Bacillariophyta, Dinophyta and Cryptophyta. From the calculations performed, the average of the models results in an increase in the maximum number of consecutive days with low rainfall (<1mm) from + 0.2 to 4.8 days / year until the year 2100, with a lower abundance of these algae being expected. On the other hand, Cyanophyta, Chlorophyta and Chrisophyta are well correlated with high values ​​of air temperature, lagoon water temperature and solar radiation. Thus, it is estimated an increase in the abundance of these algae, due to the forecasts of several models, that point to an increase in the average annual temperature in this region between 1 and 3 K until the year 2100, with reference to the period from 1961 to 1990.</p>

The Influence of South Pacific Convergence Zone Heating on the South Pacific Subtropical Anticyclone

Subtropical anticyclones and midlatitude storm tracks are key components of the large-scale atmospheric circulation. Focusing on the southern hemisphere, the seasonality of the three dominant subtropical anticyclones, situated over the South Pacific, South Atlantic, and South Indian Ocean basins, has a large influence on local weather and climate within South America, Southern Africa, and Australia, respectively. Generally speaking, sea level pressure within the southern hemisphere subtropics reaches its seasonal maximum during the winter season when the southern hemisphere Hadley Cell is at its strongest. One exception to this is the seasonal evolution of the South Pacific subtropical anticyclone. While winter maxima are seen in the South Atlantic and South Indian subtropical anticyclones, the South Pacific subtropical anticyclone reaches its seasonal maximum during local spring with elevated values extending into summer. In this study, we investigate the hypothesis that the strength of the austral summer South Pacific subtropical anticyclone is largely due to heating over the South Pacific Convergence Zone. Using added cooling and heating atmospheric-general-circulation-model experiments to artificially change the strength of austral summer diabatic heating over the South Pacific Convergence Zone, our results show that increased heating, through increased upper-level divergence, triggers a Rossby wave train that extends into the Southern Hemisphere mid-latitudes. This propagating Rossby wave train creates a high-low sea level pressure pattern that projects onto the center of the South Pacific Subtropical Anticyclone to intensify its area and strength.

Reconstructing past variations in environmental conditions and paleoproductivity over the last ∼ 8000 years off north-central Chile (30° S)

The aim of this project was to establish past variations in the main oceanographic and climatic features of a transitional semiarid ecosystem on the north-central Chilean coast. We analyzed recent sedimentary records retrieved from two bays, Guanaqueros and Tongoy (30∘ S), for geochemical and biological analyses, including the following: sensitive redox trace elements, biogenic opal, total organic carbon (TOC), diatoms and stable isotopes of organic carbon and nitrogen. Three remarkable periods were established with different environmental conditions and productivities: (1) > 6600 cal BP, (2) 4500–1800 cal BP and (3) 140 cal BP to the present (2015 CE). The first period was characterized by a remarkably higher productivity (higher diatom abundances and opal) in which large fluxes of organic compounds were also inferred from the accumulation of elements, such as Ba, Ca, Ni, Cd and P, in the sediments. Meanwhile, significantly reduced conditions at the bottom of the bays were suggested based on the large accumulation of Mo, Re and U, showing a peak at 6600 cal BP, when sulfidic conditions could have been present. According to the pollen moisture index (PMI), this was also identified as the driest interval. These conditions should be associated with an intensification of the Southern Pacific Subtropical Anticyclone (SPSA) and stronger southerly western winds, emulating La Niña-like conditions, as has been described for the SE Pacific during the early Holocene and part of the mid-Holocene. During most of the second period, lower productivity was observed; however, a small increase was identified between 3400 and 4000 cal BP, although lower amounts of diatom (valves g−1) and nutrient-type metal accumulations were evident. Anoxic conditions at the bottom of the bays changed to an almost stable suboxic condition during this time interval. The third period was marked by intense oxygenation after 1800 cal BP, as observed by a drastic change in the accumulation of U, Mo and Re. This was followed by a return to more reduced conditions over the past 2 centuries, characterized by a small productivity rise after ∼140 cal BP, as suggested by the opal accumulations. Overall, lower primary productivity, lower reduced conditions at the bottom and higher-humidity conditions were established after 6600 cal BP to the present. We suggest that the oxygenation might be associated with a weak effect from the oxygen minimum zone over the shelf and intensified El Niño activity, introducing oxygenated waters to the coastal zones through the propagation of equatorial waves and establishment of conditions that reduced the primary productivity from the mid-Holocene toward the beginning of the modern era.