Atmósfera (Journal)
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Changes in the characteristics of dry-wet periods in Xinjiang, China based on the SPEI index
Get PDFThe standardized precipitation evapotranspiration index (SPEI), calculated from 55 stations over the period 1961-2015, was used to analyze the spatial and temporal variability of the dry and wet climate in Xinjiang on a three and six-month time scale, so as to help to actively deal with the negative effects of climate change and reduce disaster losses. The obtained results show that precipitation and temperature in Xinjiang have an increasing trend, with rates of 8.90 mm and 0.39 ºC per decade, respectively. SPEI-3 and SPEI-6 show the same linear change trend, with a change rate of 0.005 and 0.007 per decade, respectively. Severe droughts occurred in 1997 and 2008, and particularly in 2008 considering SPEI-6, the number of meteorological stations with moderate drought and extreme drought accounted for 60 % of all stations. Analysis of Empirical Orthogonal Function (EOF) indicates that SPEI-3 and SPEI-6 have similar spatial distribution in the three EOF modes. EOF1 reflects that the overall dry and wet changes in the study area were weakening, and there was a drying trend; EOF2 was a reverse change in the northern and Southern Xinjiang; EOF3 shows that the East Tianshan had a drying trend, while the western part of Southern Xinjiang had a moistening trend. The spectra of wavelet coherence and cross wavelet transform showed that the SPEI values in Xinjiang have resonance periods of different time scales with the Atlantic Multidecadal Oscillation (AMO), El Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal oscillation (PDO), but shows differences in different time-domain correlations. Among them, AMO is the main atmospheric circulation factor that affects SPEI in the region
Behavior of the ITCZ second band near the Peruvian coast during the 2017 coastal El Niño
Get PDFThe behavior of the second band of the Intertropical Convergence Zone (ITCZ) near the Peruvian coast during early 2017 is studied, using precipitation, surface winds, sea surface temperature (SST) and atmospheric variables in different isobaric levels. The proposal of a daily index (Ia) to identify opportunely the formation of this band and the Lorenz energy terms in the region is also considered. This band was present from late January to early April 2017, associated with an anomalous dipole of sea level pressure between the east and west eastern Equatorial Pacific that configured anomalously northerly surface winds and the release of southeasterly trade winds near Peru. In medium levels, a zonally oriented positive mixing ratio anomaly was observed in early March over the ITCZ second band, associated with heavy rain systems over the northern Peruvian coastal region. In the same period, positive anomalies of divergence in high tropospheric levels were observed. The daily Ia index allowed an effective detection of the ITCZ second band 11 days before the maximum coastal precipitation, and the Lorenz energy terms showed eddy kinetic energy (KE) peaks in January and February and a contribution of barotropic instability in equatorial regions
Analysis of meteorological droughts in the Sonora river basin, Mexico
Get PDFDrought is a complex natural hazard that has numerous negative effects on ecosystems, agriculture, and the economy. For this reason, it is difficult to provide a precise definition. Nevertheless, different conceptualizations converge in one common denominator: the deficit of precipitation with respect to an average historical value. Droughts in Mexico have been recurrent and persistent, resulting from complex interactions of the atmosphere with the oceans and the geographic and physiographic characteristic of the country. Several researchers have approached this phenomenon with indices to characterize it using features such as intensity, duration and frequency. In this study we analyze droughts in a spatiotemporal context at scales of 3, 6, 12 and 24 months with SPI and SPEI indices at 19 weather stations located in middle and upper regions of the Sonora River basin, Mexico, for the period 1974-2013. The regions were defined according to mean annual rainfall behavior, applying statistical techniques and analyzing the physiographic characteristics of the study region. Results indicate that drought intensity increased at the end of the time series analyzed, and important periods were identified in the years 1997, 1999, 2000 and 2011 to 2013. SPEI defined the drought periods and the increasing intensity trend better than SPI, demonstrating the importance of including variables such as evapotranspiration in the balance of available water
Regional extreme rainfall estimation in the Middle Black Sea Region, Turkey
Get PDFThe occurrence probabilities of heavy rainfall that cause flood events have an essential role in designing water-related structures and water resource management. In many cases, data for analysis are either not available or are insufficient for reliable design of water-related structures. Regional frequency analysis is usually preferred to provide design information in sites with especially inadequate data available. Our study applied L-moment procedures to annual maximum rainfall series from 70 gauging stations in the Middle Black Sea Region (MBSR) of Turkey to estimate regional rainfall quantiles. The first attempt for regionalization aimed to evaluate the entire area as an homogeneous region. The sub-regions were initially defined with the ward’s clustering algorithm due to the presence of discordant sites under a presumption of a single homogeneous region. In compliance with the results of the discordancy and heterogeneity measures, the most promising classification was achieved with six clusters (sub-regions) that satisfied the homogeneity condition as “acceptably homogeneous”. It was decided that the GEV and GLO distributions in five sub-regions, the GNO distribution in four sub-regions, and the PE3 distribution in three sub-regions, were acceptable as regional frequency distributions. In comparison, GPA was not a candidate distribution in any of the six sub-regions
Regional patterns of vegetation, temperature, and rainfall trends in the coastal mountain range of Chiapas, Mexico
Get PDFChanges in atmospheric CO2, ocean temperature, and regional vegetation conditions in Mesoamerica indicate that significant trends in temperature and rainfall may have occurred in the Sierra Madre de Chiapas, Mexico. This is an important region for flora and fauna which could be affected by climate trends. We aimed to determine if and where climate trends had occurred in the Sierra Madre and lower elevation regions between 1990 and 2016 (27 years), if these trends were part of longer term (1960-2016 [57 years]) changes, and how changes in large-scale and regional/local conditions may be influencing these trends. In the Sierra Madre, overall minimum daily temperatures increased, maximum temperatures decreased, and the most significant mean temperature trends were cooler during the 27-yr period. Both the start and end of the wet season trended earlier in the year, and wet season rainfall increased significantly. Trends were not significant during the 57-yr period in the Sierra Madre; however, in the adjacent Pacific coast region, significant warmer temperature trends continued during this period. Within regions, there was large variation in temperature and rainfall changes and some local trends were opposite to the regional averages. Large-scale processes of warming sea surface temperatures in the east coast of Mexico, a change from the positive to negative phase of the Pacific Decadal Oscillation and increases in atmospheric CO2 may be influencing these trends. At the regional scale, increases in dense vegetation and evapotranspiration since 1990 may have created characteristics favoring a positive feedback of higher ocean-based moisture and vegetation-based precipitation cycling
Estimation of the pan evaporation coefficient in cold and dry climate conditions via the M5 regression tree model
Get PDFIn this study, class A pan coefficient (Kp) values were simulated via the M5 tree model, by using daily meteorological data of four stations in the East Azerbaijan province, which has arid and cold climate in the northwest of Iran. Firstly, the FAO-24 and FAO-56 methods, which are commonly used to calculate Kp values, were taken into consideration in the study. The Kp values calculated in the second stage were assumed to be observed values and were taken as the outputs of the M5 model. Four different training datasets consisting of 66, 70, 75 and 80% of the original data were tested. The best results were obtained when 70% of the data was used for training and 30% for testing. Results indicated that a Kp value was easily simulated with simple linear equations with high accuracy rate (R2 = 0.99) in all the stations. Furthermore, the Kp value was easily simulated using only two meteorological variables (relative humidity and wind speed), without the need for complex tables and equations. The most important finding of this study was the easy estimation of the Kp with a number of linear functions obtained from the M5 model; as a result, the simulated Kp can help us to calculate evapotranspiration accurately for more effective irrigation planning. The proposed method offers advantages as it is simpler and easier than the existing approaches in the literature
Rainfall uncertainty and water availability: Elements for planning water allocation to users in irrigation districts of Mexico. Study case: Irrigation District 041, Yaqui River
Get PDFThe aim of this work is to present a protocol for analyzing readily available climatic and hydrological information on watersheds, in order to achieve a rational planning of irrigation water allocation under rainfall uncertainty conditions. We present as case study the Yaqui River watershed and Irrigation District (ID) No. 041 in the state of Sonora, Mexico. The watershed is divided into three sub-watersheds that drain into three reservoirs. Our findings indicate a strong dependence of water availability on the reservoirs, conditioned by El Niño phenomenon. In addition, rainfall-runoff relationships indicate the capability to produce a runoff for each sub-watershed and the differentiated impact of El Niño. The three sub-watersheds require about the same amount of antecedent rainfall for initiating the runoff (5 mm). A standardized precipitation index (SPI) highlights the dynamics of dry and wet spells and the impact on the planted area within the irrigation district. Overall, the functional relationships between El Niño, the SPI, and the planted area in the irrigation district may serve for planning purposes under climate uncertainty scenarios
A climate analogue approach to understanding the future climates of six western South American capital cities
Get PDFFuture climate analogues were identified for six capital cities in western South America using a novel nonparametric technique and ensemble experiments. We applied the MRI-AGCM3.2H model with a horizontal resolution of approximately 60 km, three convection schemes, four sea surface temperature distributions, and two initial conditions. All ensemble experiments were conducted under scenario A1B of the Special Report on Emissions Scenarios, in which cumulative emissions are similar to those of the RCP 6.0 scenario. The majority of future analogue cities were at lower latitudes than their respective target cities. In general, all analogues of target cities had similarity scores of 0.1-0.3. Of the six analogues, four were located in central and southern Africa, whereas the remaining two were located in western South America. Projected seasonal variations in surface air temperature and precipitation in Santiago, Chile are similar to the current climate in Cape Town, South Africa, and the climate analogue for La Paz, Bolivia, is found in Oruro, Bolivia. The non-parametric method used in this study can be applied to a variety of impact assessments under a changing global climate
Intercomparison of FLEXPART and CALPUFF dispersion models. An application over a small tropical island
Get PDFA typical practice in air quality modeling assessment is the intercomparison between different dispersion models results and air quality measurements at different atmospheric conditions. In this study, a comparison between the results of two Lagrangian dispersion models, the Lagrangian Particle Dispersion Model FLEXPART and the Lagrangian Puff Model CALPUFF (regulatory model), coupled to the same meteorological fields produced by the Weather Research and Forecasting (WRF) model, was done. As a case study, atmospheric dispersion of anthropogenic nitrogen oxides (NOx) emissions (considered as a passive tracer) was considered, during a typical case of severe pollution over the densely populated area of the Guadeloupe archipelago (West French Indies), including complex terrain and, of course, coastal influence. Even though Lagrangian models usually provide better results of plume dispersion under strong winds, in this case study weak trade winds are dominant, in order to check both models under non-ideal atmospheric conditions. As a result, compared to NOx ground level concentration (glc) observations, FLEXPART shows better agreement than CALPUFF. However, as a regulatory model, CALPUFF overestimates both glc observations and FLEXPART maximum NOx glc results, with higher values when a higher horizontal resolution is applied. Also, differences between models results arise in the spatial distribution of NOx over a 1 × 1 km2 horizontal resolution grid domain, showing quite homogenous isopleths with smooth contours for CALPUFF vs. fragmented isopleths with irregular contours for FLEXPART
Relationship between daily atmospheric circulation patterns and South Atlantic Convergence Zone (SACZ) events
Get PDFThis study presents the daily atmospheric circulation patterns at surface and altitude related to the South Atlantic Convergence Zone (SACZ) events that occurred between 2007 and 2017. For this analysis, Principal Pattern Sequence Analysis (PPSA) and sea level pressure and geopotential height reanalysis were used. Four typical atmospheric circulation patterns associated with SACZ episodes were identified. Three of them are related to the propagation of a cold front toward southeastern Brazil with a post-frontal anticyclone moving over the Atlantic Ocean. The fourth pattern is associated with the presence of a cut-off low centered over the central-south region of Brazil that induces moisture transport from the Atlantic Ocean and from the Amazon basin to most of southeastern Brazil. Considering the first three patterns, they represent, respectively, a frontal wave, a classical cold front, and a slow-moving cold front. All of these patterns provide permanent northwesterly winds in the lower troposphere over southeastern Brazil from two days before the SACZ occurrence