Search

The recovery of early records of maximum, minimum, and mean temperatures; pressure; and relative humidity measurements in Puerto Madryn for the period 1902–1915 is presented. A careful evaluation of the quality of the data was performed using internal coherence, tolerance, and temporal consistency tests. The monthly mean series of all the variables, constructed from daily raw data, were subject to several homogeneity tests, and only discontinuities in pressure and relative humidity were found. The homogenized monthly mean series were compared with the Twentieth Century Reanalysis series in annual and seasonal time steps. In addition, the trends of each variable were assessed using the Mann–Kendall procedure, and correlations between relative humidity and the other variables were examined. The results show a remarkably good agreement between the temperature measurements and reanalysis values with a Spearman correlation coefficient of 0.94. The raw data for minimum and maximum temperatures represent a very good upper and lower bound for the mean temperature values of both observational and reanalysis data. Agreement was found to be lower for relative humidity and pressure with the correlation coefficients being close to 0.6 in both cases. No trends were found for the variables. The correlation analysis of the humidity measurements with the other variables shows an inverse dependence of the temperatures and no relatedness with the pressure values. [ABSTRACT FROM AUTHOR]

A climate analysis of the monthly mean temperatures of Southern Patagonia during the late-XIXth and early-XXth centuries was carried out as part of the international data rescue Atmospheric Circulation Reconstructions over the Earth (ACRE) program partnership in Argentina, together with other data sources with regional and global records. The data from these diverse sources were combined to carry out a study in the coastal region of Patagonia, including Tierra del Fuego, between 42° S and 55° S for 11 locations. Furthermore, HadSST monthly/seasonal fields during the period 1880–1920 were also used. Both mean monthly and seasonal temperature values and timeseries variability were considered. Their analysis shows consistent behavior within the study region and compared to Southern Hemisphere mean results, which are characterized by a warm late-XIX century and a cooler early-XX century. This is also in agreement with SST variability along the coasts of Patagonia and hemispheric records. A comparison with present-day observations, where available, also yields consistent behavior. Low-frequency variability, i.e., in periods longer than 3 years, during the study period is consistent with present variability. Trend estimates at Trelew and Rio Gallegos for the period 1901–2020 yield significant trends, consistent with hemispheric warming at their latitudes. [ABSTRACT FROM AUTHOR]

The international Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative works to recover global climate history and build an accessible databank, with data from the past 250 years of terrestrial and marine surface. Argentina is part of that effort with ACRE Argentina recovering data from various sources that have been recorded throughout the country since the 19th century. In this paper, weather observations transcribed from the original records into digital form and taken every day during the years 1860–1879 at Bahía Blanca and from 1873–1886 at Corrientes are presented. The digitization was carried out through the project Meteorologum ad Extremum Terrae (MET) launched in the Zooniverse interface, which is currently working with near 900 citizen scientist volunteers per day. The present analysis corresponds to data retrieved from the collection 'Anales de la Oficina Meteorológica Argentina' and contains information on atmospheric pressure, air temperature, relative humidity, cloud cover, cloud types, wind direction, wind speed, rainfall and weather remarks. For the present analysis, only temperature and pressure values, measured in °C and mm of Hg, respectively, were considered, after a quality control of the digitization process was applied. Data values were tested and used to rebuild the time series of both places and correlation with SOI index and monthly pressure values for both places was tested using Spearman correlation. Results show that the influence of El Niño episode during 1877–1878 can be found in the pressure values at Corrientes. [ABSTRACT FROM AUTHOR]

An updated climatology for the occurrence of blockings in the Southern Hemisphere (SH) using daily reanalysis data from 1948–2021 is presented. Geopotential height (z) at 500 hPa was the working variable. The blocking index (BI) was defined for every 2.5° of longitude whenever z (35 °   S) − z (50 °   S) < 0 . The results were organized in longitudinal bands of a width of 10° in order to compare them with previous findings. The primary region for the occurrence of blockings was located around the date line, with a secondary region in southern South America (SSA) and its vicinities, with a third-rank region situated in southern Africa and its surroundings. The results were also stratified by the intensity and duration (persistence) of the events, and the annual and seasonal differences were discussed. Additionally, three different areas were defined to study the distribution of the blockings therein, with the Pacific region (110° E–80° W) having the maximum intensities and longest durations. Linear trends were estimated for the annual and the seasonal time series of the BI and for the number of episodes. On an annual basis, more frequent and the strongest events are expected at 180° E and their surroundings in the future. An alternative BI, using radiosonde data, was built for SSA at 58.50° W. The time evolution of this index was in general agreement with the one estimated from the reanalysis data at some longitudes. [ABSTRACT FROM AUTHOR]

Extra‐tropical cyclones are a relevant feature in the climate at middle and high latitudes. Despite their importance, most studies typically focus only on cyclones identified at a single atmospheric level and on events close to the surface. This paper provides a new perspective on the Southern Hemisphere (SH) cyclone events based on the multilevel cyclone tracking algorithm STACKER. The algorithm, using relative vorticity, detects the raw tracks at single levels and objectively combines them to provide the 3D events and their evolutionary timeline. As a result, a 3D cyclone climatology, based on ECMWF Reanalysis ERA‐I data from 12 pressure levels in the troposphere and lowermost stratosphere is presented. To the best of our knowledge, this is the first analysis carried out throughout the troposphere and the lowermost extratropical/subpolar stratosphere in order to give a comprehensive picture of the cyclone events as physical entities throughout their lifetime. Cyclone properties analysed are track densities, translational velocity, vorticity and lifetimes. For the subtropical and extra‐tropical SH, results support many previous ideas about cyclone characteristics, but new insights are also obtained. A total of 58,231 multilevel cyclone events lasting at least 2 days were detected, with vertical structures spanning two or more levels. This means an average of 303 cyclone events of all types per month, between 2001 and 2017, disregarding seasonality. Results show that cyclones are most frequently detected at the lowest levels of 925 and 700 hPa. By considering that cyclonic systems can be grouped into families according to their vertical extent, results per month on average show that shallow systems are the most frequent events with approximately 248 systems detected, followed by 43 intermediary and 11 deep events. Shallow and deep systems have a large percentage of events with genesis at 925 and 700 hPa. Density statistics show that shallow events are present at all latitude ranges mostly poleward of 30°S with high‐ and medium‐intensities, while intermediate ones are mostly restricted to mid‐latitudes and deep events are mostly confined to sub‐polar and polar latitudes. Cyclones over Antarctica seem to be mostly intermediary and deep cyclones, with longer lifetimes and lower velocities. [ABSTRACT FROM AUTHOR]

Annual anomalies of Lambertian equivalent reflectivity (LER) retrieved from the total ozone mapping spectrometer spanning the period November 1978–November 2005 were studied in the Southern Hemisphere, in a region bounded by 0° S and 60° S, and their trends were estimated. With the exception of few regions where the variable may represent the contribution of both cloudiness and snow, trends in LER anomalies provided an evolution of total cloudiness. On average, the study region experienced a net increase in LER values of 0.78 reflectivity units (RU) decade−1; if only significant trend values are considered this figure increased to 1.18 RU decade−1. The region that showed the largest upward trend, up to 4 RU decade−1, was located over the eastern Pacific, off the coasts of Chile and Peru, where the presence of marine stratocumulus is frequent. Despite the overall positive trend there were regions that yielded a negative one, most notably the tropical latitudes of South America and Africa. The yearly zonal means also showed a positive trend at all latitudes, but significance occurred beyond 20° S only. Correlation maps between LER anomalies and five different circulation indices were also introduced. The indices with the highest and lowest number of significant correlation values were the Madden–Julian oscillation at 70° E and the quasi-biennial Oscillation, respectively. [ABSTRACT FROM PUBLISHER]

Differences between lapse rate tropopauses ( LRTs) and LRT-like tropopauses retrieved from mandatory levels ( LRTMs) were studied for height, pressure and temperature at 37 locations of the Indian subcontinent on a long-term annual, summer and winter basis covering the period 1973-2015. LRTM is usually found below LRT and statistical distinctions hinder the use of the former tropopause as a replacement for the latter one, yet significant positive Spearman's correlations show a relationship through a monotonic increasing function that enable the estimation of LRT variables from the corresponding LRTM ones. The slope and the intercept for a linear function relating corresponding variables were obtained at each location. [ABSTRACT FROM AUTHOR]

A seasonal climatology for the Lambertian equivalent reflectivity (LER) in ultraviolet (UV) for southern South America is introduced. The study region was limited by 10° and 60°S and by 100° and 30°W; the data set spanned the period 1978–2015. Features of the seasonal means and of the quarterly (Q) and the interannual (IA) variabilities for each season were ascribed to atmospheric and oceanic processes of local, regional, or global origin which lead to the formation or maintenance of clouds. Shifts in the Q and IA time series were detected, most notably in the early 1990s. Linear trends were also estimated. The largest positive and negative trends in the Q time series were found along the Peruvian Andes (PA) (3.20 reflectivity units [RU] decade−1) and east of the Chapada Diamantina (CD) and the Serra do Espinhaço (SE) in Brazil (−1.40 RU decade−1), respectively. The largest positive and negative trends in the IA time series were found in PA (6 RU decade−1, summer) and east of CD and SE (−2.50 RU decade−1, spring), respectively. The linkages between UV LER and regional or global circulation indices were also studied. The largest relationships were found with the Dipole Mode Index on a Q basis and with the Southern Oscillation Index on an IA basis in winter. [ABSTRACT FROM AUTHOR]

An unrotated principal components analysis was carried out to establish the most representative modes for the joint variability between the heights of the upper and lower boundaries of cirrus clouds and three different mandatory levels (850, 500, and 100 hPa), and the associated stability of the troposphere over Buenos Aires. Discussion is limited to the first three most representative structures found, which consists of spatial patterns (or empirical orthogonal functions, EOFs) and their time-evolving coefficients (or principal components, PCs). EOF1shows a direct (indirect) mode that encompasses the cirrus slightly below (above) its mean position, with 500 and 100 hPa exhibiting a similar behaviour and 850 hPa acting the opposite way. EOF1is associated with above-normal stability (instability) for direct (indirect) modes (i.e. positive (negative) values of PC1). On a monthly average, this occurs in the austral winter (summer) months. Regarding EOF2, all three mandatory levels experience positive (negative) height anomalies in direct (indirect) modes and cirrus goes up (down) under mild stability (instability). Monthly averages show that PC2is approximately positive in summer and in early fall and negative the rest of the year. As to EOF3, it is characterized by a stability similar to that of EOF2, with direct (indirect) modes showing lowered (raised) cirrus and all three mandatory levels above (below) normal conditions; on a monthly basis, PC3is best described as having a semi-annual evolution, with maxima (minima) in March and October (January and August). Overall, EOF1has the highest stability or instability, depending upon the sign of PC1. These results are the first of their kind worldwide. [ABSTRACT FROM AUTHOR]

A method for the detection of inhomogeneities in time series was used to analyze the presence of breaks in the regime and climate shifts in monthly mean time series of single thermal tropopause pressure, height and temperature, at radiosonde stations located in India and southern South America, for the period 1973-2011. The method is based on fitting the data with a function that gets closer to a step function depending on a modifiable parameter, and to estimate the signal-to-noise ratio within a mobile window of variable width that is centered at each point of reference in the time series. There will exist an inhomogeneity at a given point of reference anytime exceeds a theoretical critical value γc. Since this value is hard to be estimated, an alternate calculation that depends on the analyzed data was carried out. Unlike similar methods for which γc = 1 is established, the analysis here determines γc for each month and for different window timescales. It is found that γc decreases with an increasing width of the timescale, fulfilling the condition γc = 0,5 i.e. a constant value, only for the longest timescales. From a joint analysis that included all cases for which γ> γc and certain time windows, inhomogeneities with climatic shift features were found over the extratropical region of South America in 1993, and over the subtropical region of India around 2001. [ABSTRACT FROM AUTHOR]

The article presents a study on the association between the standardized tropopause height anomalies (STHAs) and standardized 500 and 100-hectopascal (hPa) height anomalies based from their latitudinal heights. It says that the study utilized a FORTRAN program to compute the tropopauses which were obtained from significant levels. It mentions that using the empirical orthogonal functions (EOFs), it was revealed that tropopause height correlates with the temperature in the lower stratosphere.

An unsupervised k-means/k-means++ clustering algorithm was implemented on daily images of standardized anomalies of brightness temperature (T b) derived from the Geostationary Operational Environmental Satellite (GOES)-13 infrared data for the period 1 December 2010 to 30 November 2016. The goal was to decompose each individual T b image into four clusters that captures the characteristics of different cloud regimes. The extracted clusters were ordered by their mean value in an ascending fashion so that the lower the cluster order, the higher the clouds they represent. A linear regression between temperature and height with temperature used as the predictor was conducted to estimate cloud top heights (CTHs) from the T b values. The analysis of the results was performed in two different ways: sample dates and seasonal features. Cluster 1 is the less dominant one, representing clouds with the highest tops and variabilities. Cluster 4 is the most dominant one and represents a cloud regime that spans the lowest 2 km of the troposphere. Clusters 2 and 3 are entangled in the sense that both have their CTHs spanning the middle troposphere. Correlations between the monthly time series of the number of pixels in each cluster and of the entropy with several circulation indices are also introduced. Additionally, a fractal-related analysis was carried out on cluster 1 in order to resolve cirrus and cumulonimbus. [ABSTRACT FROM AUTHOR]