Atmósfera (Journal)
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Influence of Santa Ana winds on the surface circulation of Todos Santos Bay, Baja California, Mexico
Get PDFThe influence of easterly and northeasterly dry and warm Santa Ana winds (SAw) on the surface circulation of Todos Santos Bay, Mexico, is studied from surface currents and wind data measured during the most extreme periods of activity (autumn-winter season). Sea surface currents were measured using a system of coastally-based HF radar stations between 2009 and 2015. Winter-mean surface circulation showed a cyclonic tendency. Atmospheric variables allowed the grouping of ~122 SAw events, 23% of which caused a noticeable change in the background circulation. Event-mean current patterns showed dissimilar responses to the acting winds, with some SAw events driving weak offshore currents, another that developed an eddy-pair circulation inside the bay, and one rather intense (winds of 8-10 m s–1) that developed a clockwise circulation overturning the cyclonic long-term winter-mean. In general, changes in the circulation were related to an offshore transport of surface waters into the open ocean
A rare winter thunderstorm event near Hong Kong
Get PDFA rare winter thunderstorm event near Hong Kong is documented in this paper. The thunderstorm occurrence was confirmed by the observation of one of the authors and lightning location information systems (both regional and global). It developed over the frontal cloud band associated with the winter monsoon. Observing the upper air measurements, however, the thermodynamic conditions did not seem favorable to the occurrence of the thunderstorm. The convective available potential energy could not be determined in the cool and dry lower troposphere. There was only a moister layer in the middle troposphere. The weather forecaster did not anticipate the occurrence of thunder and lightning. However, some features could have changed dynamically, which suggested the possibility that a thunderstorm would take place. For instance, waves could be identified in the middle troposphere and a broad troughing flow could be analyzed in the lower troposphere. The integrated wave vapor was also of a rather high level. It is hoped that this paper can serve as a useful reference for forecasters in assessing the possibility of thunderstorms occurring during winter over subtropical latitudes in association with frontal cloud bands
Dependence of extreme precipitable water events on temperature
Get PDFRecent IPCC reports suggest that the world is getting warmer. Consequently, the concentration of atmospheric water vapor, which determines the water for precipitation, is substantially increasing in accordance with the Clausius-Clapeyron (CC) relationship, which establishes that water vapor in the atmosphere increases at a rate of 7% per ºC of warming. In this study, we explored the relationship between extreme precipitable water events and temperature over the whole globe, its two hemispheres, and the 5º latitudinal bands by using NCEP/NCAR and MERRA-2 reanalysis data for 1980-2017. Our results indicate that extreme precipitable water events linked to temperature basically follow the CC relationship at temperatures roughly below 5 ºC and the sub-CC relationship for temperatures above ~5 ºC, globally and in both hemispheres. The relationship between extreme precipitable water events and temperature over latitudinal regions is not uniform and varies regionally. Our results further indicate that the increasing rate of extreme precipitable water events is higher in the tropics and mid-latitudes of the southern hemisphere than in the northern hemisphere. This study shows the usefulness of the principle of Clausius-Clapeyron relationship to explain extreme precipitable water events linked to temperature
Analysis of a severe air pollution episode in India during Diwali festival – a nationwide approach
Get PDFAir pollution events have been a subject of major concern worldwide in recent years, since their frequency and intensity is increasing with time. An alarmingly high air pollution episode was observed in some parts of India during late October to the end of November in the year 2016. The Air Quality Index was observed to vary from poor to severe in northern and western parts of India, while it was satisfactory to moderate in the east and south of the country. The causes of this observed high pollution episode are examined in this paper. Apart from the Diwali effect on air pollution the study findings indicated the importance of biomass burning over India.
An exploration of the aerosol indirect effects in East Asia using a regional climate model
Get PDFIn this study, the aerosol direct, semi-direct and indirect effects on the East Asia climate are investigated using the International Center for Theoretical Physics Regional Climate Model v. 4 (RegCM4.1.1), by focusing on the East Asian Summer Monsoon temperature and precipitation. The externally mixed aerosols, including sulfate (SO42–), black carbon and organic carbon, reduced the solar flux reaching the surface directly by scattering solar radiation, and indirectly by increasing the cloud droplet concentration and cloud liquid water path over East China. The combined aerosol effects (direct and indirect) decreased the temperature on the continent and increased it over the oceans, leading to the reduction of rainfall in the central regions of China and an enhancement of rainfall in the adjacent ocean regions
Spatio-temporal analysis of the droughts in Cali, Colombia and their primary relationships with the El Niño-Southern Oscillation (ENSO) between 1971 and 2011
Get PDFThis paper analyzed the spatio-temporal variability of droughts in Cali, Colombia and their primary relations to the El Niño Southern Oscillation (ENSO). The Standardized Precipitation Index (SPI) was used to detect drought events from monthly rainfall data of 24 stations well spread over Cali during 1971-2011. The SPI provided the drought intensity, magnitude, frequency, and the minimum rainfall thresholds, mainly on an annual scale (SPI-12). Eighty percent of the stations reported four events with dry conditions in Cali: 1976-1977, 1983-1984, 1990-1992 and 2009-2010. The ENSO influence was evaluated using the correlation and wavelet transform analyses. Significant (non-significant) negative correlations between SPI-12 in the northern (southern) part of Cali, the multivariate ENSO Index (MEI), and Sea Surface Temperature (SST) Niño 3.4 and Niño 4 indices were observed. The wavelet coherence analysis showed significant coherencies between ENSO and SPI-12: at interannual scale (4-6 years), the phase difference of –135º generates a lag of 6-9 months between the minimum peak of the SPI-12 and the maximum peak of the indices. On the quasi-biennial scale (2-3 years), the phase difference of –180º suggests that the maximum wet (dry) conditions coincide with the mature stage of the La Niña (El Niño) event; and on the decadal scale (8-16 years), the decreases (increases) in rainfall precede the El Niño (La Niña) mature stage by approximately 10-18 months. These results are relevant for seasonal forecasting, since changes in SST in the equatorial Pacific may take place 6-18 months ahead of the dry conditions in Cali
Trends and rainfall tropicalization in Paraná State, south of Brazil
Get PDFIn order to detect areas and periods of rainfall reduction and increase in Paraná State, south of Brazil, the objective of this manuscript is to analyze, spatially and temporally, rainfall trends from 1976 to 2011. Monthly data were collected on accumulated rainfall (mm) from 63 pluviometric stations distributed throughout the study area. The data were grouped into quarterly (autumn, winter, spring, and summer), seasonal (dry and rainy season), and annual values. All values were evaluated for homogeneity and trends using the Mann-Whitney-Pettitt, Mann-Kendall, and linear regression tests. The results indicate a rainfall transition detected in the period 1991 to 1999, with a maximum change point in 1993. The trends indicate an average increase of 4.03 mm in the rainy season, mainly in the sectors that are predominately subtropical and coastal climates. These results corroborate in a better explanation rainfall patterns and variability in the tropical regions and the Southern Hemisphere, and imply a moderate process of rainfall tropicalization in the subtropical climate of Paraná State
Evaluation of WRF parameterizations for global horizontal irradiation forecasts: A study for Turkey
Get PDFThis study deals with the evaluation of the Weather Research and Forecast (WRF) model’s parameterization schemes when used for global horizontal irradiation (GHI) forecasts, to assess the feasibility of solar energy utilization. The study area is the southeastern Anatolia (SEA) region of Turkey, with favorable weather conditions for solar energy generation. The results indicate that the values in the hourly output of GHI in the model were overestimated for all configurations at all stations compared to observations. The relative mean bias error values at five stations for all configurations vary between 10-21% for clear-sky and 17-30% for partly-cloudy conditions. Similarly, the relative RMSE values at the five stations vary between 20-39% for clear sky and 41-70% for partly-cloudy conditions. However, there are noticeable differences among the various configurations of the WRF parameterizations
A historical climatology of the easterly winds in the strait of Gibraltar
Get PDFIn this paper, we use historical wind direction observations taken aboard sailing ships to build a new index for the frequency of the easterly winds in the strait of Gibraltar, in southern Spain. The new series starts in the late 19th century, adding almost 100 years to comparable previous series. We have found large interannual and decadal fluctuations in the frequency of the easterly winds in Gibraltar along the 20th century, although no long-term trends have been revealed. We show that the changes in the frequency of the easterly winds in Gibraltar appear significantly related to the North Atlantic Oscillation and to anomalies in the sea level pressure across the North Atlantic and large areas of Europe
Streamflow modeling of five major rivers that flow into the Gulf of Mexico using SWAT
Get PDFIt has been shown that detailed and continuous riverine discharge and nutrient input data are fundamental to the successful simulation of biogeochemical processes in the ocean using numerical models. Currently, no discharge data for the river mouths on the Mexican side of the Gulf of México (GoM) is available. In the present study, the Soil and Water Assessment Tool (SWAT) was used to simulate the daily discharge of five major rivers that flow directly into the GoM. Two periods were used in the analysis: 1997 to 2013 for the Grijalva basin and 1989 to 2013 for the Usumacinta, Papaloapan, Coatzacoalcos, and Pánuco basins. The model was successfully calibrated for monthly time steps using an automatized technique for the five watersheds. The sensitivity analysis of the calibration process showed that for most of the watersheds, the model was sensitive to groundwater and soil moisture parametrizations