Classificação sinótica dos campos de pressão atmosférica na América do Sul e sua relação com as baixas do chaco e do noroeste argentino Synoptic classification of the atmospheric pressure fields over South America and its relation to the Chaco and the Argentinean Northwest Lows

O trabalho apresenta uma classificação dos campos de pressão atmosférica ao nível médio do mar sobre América do Sul, durante as estações de verão e inverno, com o intuito de identificar os principais padrões sinóticos associados à Baixa do Noroeste da Argentina (BNOA) e à Baixa do Chaco (BCH). Para isso, a técnica de Análise de Componentes Principais rotacionadas foi aplicada à serie de reanálises do NCEP para o período 1985-2010. Um segundo objetivo foi determinar as principais frequências de variabilidade relacionadas com a atuação de ambos os sistemas, mediante a utilização do método de Análise Espectral. Os resultados destacam cinco padrões de circulação que representam aproximadamente 80% dos casos analisados. Durante o verão, a BCH, localizada entre o norte da Argentina, Paraguai, Mato Grosso do Sul e o sul da Bolívia, está associada principalmente com dois padrões sinóticos. A BNOA está associada apenas com um padrão sinótico, similar ao campo médio sazonal. Já no inverno, a BCH não aparece, confirmando seu caráter térmico, gerada principalmente pela liberação de calor latente, produto da convecção observada na área de atuação deste sistema. A BNOA também está associada apenas com um padrão sinótico durante esta estação. Este padrão é similar ao obtido no verão, porém representando menor porcentagem de variância e relacionado principalmente com perturbações sinóticas. A análise de frequência mostra que o modo de circulação associado à BCH tem um pico de energia em torno dos 17 dias, enquanto que a BNOA apresenta um pico de energia em torno dos 22 dias durante o verão e um relativo aumento da variabilidade sinótica no inverno.<br>This work performs a classification of sea level pressure fields for South America during summer and winter, in order to identify the main synoptic patterns associated with the Northwestern Argentinean Low (NAL) and the Chaco Low (CHL). To this purpose, the Principal Component Analysis technique in rotated mode was applied to the NCEP reanalysis for the period from 1985 to 2010. A second objective was to determine the main variability frequencies related to both systems, by employing Spectral Analysis. The results provide five circulation patterns, representative of about 80% of all cases. During summer, the CHL, located between northern Argentina, Paraguay, Bolivia and southern MS, is mainly associated with two synoptic patterns. The NAL is associated with a single synoptic mode, similar to the seasonal mean field. During winter, the CHL is not recognized, in agreement with its thermal nature related to latent heat released by tropical convection. The NAL is also associated with a unique synoptic mode during this season. This mode is similar to that obtained in the summer and is also related to synoptic scale disturbances but explaining a lesser percentage of variance. The Frequency Analysis show that the circulation mode associated to the CHL has an energy peak at around 17 days, while the NAL has an energy peak around 22 days in summer and a relative increase of synoptic variability in winter

State of Climate in 2012

For the first time in several years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Niña dissipated to ENSO-neutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern equatorial Pacific uncharacteristically returned to neutral conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Niña-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in global sea level in the first half of 2011 that were linked to the effects of La Niña, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near- or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in the Western North Pacific basin. Of these, Super Typhoon Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7°N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global financial crisis, global C

State of the Climate in 2012

International audienceEditors note: For easy download the posted pdf of the State of the Climate for 2012 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download