Atmósfera (Journal)
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Performance of cumulus parameterization schemes in the simulation of Indian Summer Monsoon using RegCM4
Get PDFThe Indian Summer Monsoon (ISM) is driven by organized large-scale convection; hence, its simulation is expected to depend on an appropriate representation of cumulus convection in the model. In the present study, the performance of different cumulus parameterization schemes is examined towards simulations of the ISM. The Regional Climate Model (RegCM4) is coupled with the Community Land Model (CLM 3.5) at 30 km resolution for the period May 1-September 30 for seasonal simulation of the ISM in three consecutive years, 2007, 2008, and 2009. Five numerical experiments with five convection schemes (Kuo, Grell, MIT, GO_ML [Grell over ocean and MIT over land], GL_MO [Grell over land and MIT over ocean]) are conducted for each of these three years. Some important features of the ISM simulated by the model, viz. low level westerly jet, upper level easterly jet, heat low, Tibetan high, etc., are analyzed and compared with that of the National Center for Environmental Prediction (NCEP) reanalysis. We found that the heat low over northwest India and Pakistan in all the three years is better simulated by the model with the MIT convection scheme compared to other convection schemes, whereas spatial distribution and accuracy of surface temperature is better simulated using GL_MO rather than MIT. The low level westerly jet is well captured by the model with MIT with slightly weaker strength compared to the National Center for Environmental Prediction (NCEP) reanalysis. The location and strength of the tropical easterly jet is well predicted in each simulation with some uncertainty in strength, and are better simulated with MIT. The comparison of the model simulated rainfall with 0.5º × 0.5º datasets from the Climate Research Unit (CRU TS3.22) indicates that seasonal and monthly average rainfall are well simulated with MIT and GO_ML; however, the same over central and western India is significantly underestimated by the model with all the convection schemes. Comparatively, higher sensible heat flux and lower latent heat flux are noticed in the model simulation with all schemes. This change of fluxes affects surface temperature and rainfall simulation significantly. The statistical analysis indicates that surface temperature and rainfall are well reproduced by the model with GL_MO and GO_ML, but circulation is better simulated with MIT only. It is observed that although the bias in the model with MIT is slightly higher than that of the two mixed schemes, the spatial distribution and other synoptic features of surface temperature and rainfall during ISM are well simulated. Thus, considering overall performances, the RegCM4 with MIT the cumulus convection scheme provides better simulation of seasonal and monthly features of the monsoon
Seasonal changes in the PM1 chemical composition north of Mexico City
Get PDFAn Aerodyne Aerosol Chemical Speciation Monitor (ACSM; Aerodyne Inc.) was deployed at a site north of Mexico City from November 13, 2013 to April 30, 2014 to investigate the seasonal variability of the chemical composition of submicron particles. The ACSM provides real time information on mass concentration of the non-refractory main species (nitrate, sulfate, ammonium, chloride and organic compounds) in particulate matter less than 1 μm (NR-PM1) with a 30-min time resolution. Meteorological variables (temperature, relative humidity, and wind speed and direction), as well as concentrations of black carbon, PM1, PM2.5, CO, SO2, NO, NO2, and O3, were also measured. The total NR-PM1 mass concentrations plus black carbon (which must be close to the PM1 total mass) showed a good correlation with PM1 mass concentration measured with a Tapered Element Oscillating Micro-Balance, an indication of the soundness of the ACSM data. In average, the composition of the aerosol as well as its diurnal variability were similar to observations in previous studies using similar instruments (MCMA-2003 and MILAGRO). However, it was observed that the aerosol was persistently acidic during November and December probably due to a higher relative humidity, lower temperature, and more frequent winds from the NW, where the Tula industrial complex is located. A lower concentration of ammonia (NH3) in the gas phase might affect the PM acidity too. These results suggest a seasonal variability in the aerosol chemistry in Mexico City, which should be verified with more long-term studies
The impact of climate on farm inputs in developing countries agriculture
Get PDFThe success of the green revolution has prompted some analysts to suggest it can be extended more broadly to all poor farmers. This paper argues that suitable natural endowments are an important precondition for high input farming. Examining production functions across China, we find that outcomes are very climate sensitive. It follows that we also find that input demand functions are climate sensitive. Efforts to intensify farming in undeveloped regions should focus on places with suitable soils and especially climate. The results also suggest that farmers will partially adapt to climate change by altering their input intensity
Characterizing and attributing the warming trend in sea and land surface temperatures
Get PDFBecause of low-frequency internal variability, the observed and underlying warming trends in temperature series can be markedly different. Important differences in the observed nonlinear trends in hemispheric temperature series suggest that the northern and southern hemispheres have responded differently to the changes in the radiative forcing. Using recent econometric techniques, we can reconcile such differences and show that all sea and land temperatures share similar time series properties and a common underlying warming trend having a dominant anthropogenic origin. We also investigate the interhemispheric temperature asymmetry (ITA) and show that the differences in warming between hemispheres are in part driven by anthropogenic forcing but that most of the observed rapid changes is likely due to natural variability. The attribution of changes in ITA is relevant since increases in the temperature contrast between hemispheres could potentially produce a shift in the Intertropical Convergence Zone and alter rainfall patterns. The existence of a current slowdown in the warming and its causes are also investigated. The results suggest that the slowdown is a common feature in global and hemispheric sea and land temperatures that can, at least partly, be attributed to changes in anthropogenic forcing
Population and trends in the global mean temperature
Get PDFThe Fisher ideal index, developed to measure price inflation, is applied to define a population-weighted temperature trend. This method has the advantages that the trend is representative for the population distribution throughout the sample but without conflating the trend in the population distribution and the trend in the temperature. I show that the trend in the global area-weighted average surface air temperature is different in key details from the population-weighted trend. I extend the index to include urbanization and the urban heat island effect. This substantially changes the trend again. I further extend the index to include international migration, but this has a minor impact on the trend
Effect of different pavements on human thermal comfort conditions
Get PDFThe urban heat island (UHI) phenomenon and outdoor human thermal comfort may be affected by several factors such as the size of the built environment, the rate of open and green spaces and different types of ground surface covers (e.g., grass and artificial covers) in urban areas. Depending on the types and structures of the pavement/covering materials, which can have effects on the albedo and surface heating, ground surfaces reflect solar radiation or heat the air above them. Pavements that can absorb more solar radiation may turn it into heat, thus warming the air, which in turn heats urban areas and make them uncomfortable for human beings. The present study investigates the effect of different materials on the UHI intensity by considering nine different types of materials (andesite, granite, basalt, travertine, impregnated wood, soil, asphalt, clinker powder and grass) in the Ata botanical garden located in the city center of Erzurum, in the Eastern Anatolia region of Turkey. Temperature data were measured on clear summer days during the month of July and compared in terms of thermal comfort. All measurements were taken 150 cm above the ground at 12:00 p.m. by using an infrared thermometer (CEM-DT-8812). In order to estimate the physiologically equivalent temperature (PET) for each soil type, data were analyzed using the RayMan 2.1 software, and the scores were statistically analyzed with analysis of variance (ANOVA). The differences in mean temperatures were evaluated with Fisher’s least significant difference (LSD) test. The results showed that mean PET scores ranged between 28.9 ºC for impregnated wood and 25.9 ºC for grass (a difference of 3.0 ºC), while the other scores were 26.1, 26.7, 27.1, 27.5, 27.8, 28.5 and 28.5 ºC for travertine, granite, andesite, soil, clinker powder, basalt, and asphalt, respectively. The analytical results indicated that all the studied materials create a slight heat stress (23.1-29.0 ºC) according to their PET indices and their predetermined comfort intervals. However, the levels of heat stress for impregnated wood, asphalt, and basalt were higher than the others. It was determined that grass, travertine and cube granite are optimal surface materials, since they exhibited a level of heat stress that is close to the comfort range (18.1-23.0 ºC)
Effects of El Niño in Mexico during rainy and dry seasons: an extended treatment
Get PDFThe effect of El Niño-Southern Oscillation (ENSO) on precipitation in Mexico is analyzed. Unlike previous studies, the amount of data used is larger and the Mexican territory is more widely covered. In this paper, daily precipitation from the CLICOM database updated to 2015 was used. The studied period spans from 1961 to 2013 and was divided into two periods: 1961-1990 and 1991-2013. For the same periods two separated seasons were considered: the cold and dry (November-April), and the warm and wet (May-October). Thus, the number of stations that exceed the amount of continuous information criteria for a certain period increases considerably. The Pearson correlation coefficient with a significance of 5% was used in order to test for the existence of a relationship between precipitation and the Multivariate ENSO Index (MEI). The results are presented in maps where regions of precipitation above or below average are observed. During the summer/warm months, the northwestern region of Mexico is clearly identified with a direct relationship between MEI and precipitation, whereas an inverse relationship in the part that lies south of latitude 22º N is seen. In the winter/cold months, there is a general increase in precipitation with increasing MEI. Distributions of normal rainfall for both winter and summer are also shown
Ozone climatology and variability over Irene, South Africa determined by ground based and satellite observations. Part 1: Vertical variations in the troposphere and stratosphere
Get PDFIn this investigation, the climatological characteristics of ozone over Irene (25.5º S, 28.1º E) are studied with the aid of both ground-based and satellite observations. The principle aim of this work is therefore to examine the variability of vertical ozone distribution over Irene. Ozonesonde measurements and satellite measurements in the mesosphere-lower thermosphere region from the Microwave Limb Sounder (MLS) onboard the Aura satellite and it measures for the period 2004-2007 are employed in this study. The MLS satellite measurements are collected when it overpasses Irene. The vertical ozone profiles are obtained from ozonesondes and the MLS and are found to be in good agreement from a 15 km altitude and above. Maximum ozone concentration is found in the altitude between 23-27 km. The monthly variation of ozone concentration measured by ozonesondes and MLS show maximum and minimum concentrations during spring and autumn, respectively. During spring, the maximum ozone concentration measured by ozonesonde is 4.5 × 1012 molecules cm–3 while that measured by the MLS instrument is ~4.1 × 1012 molecules cm–3. A difference in the range of 0.4 × 1012 to 0.8 × 1012 molecules cm–3 was obtained for all seasons except during winter, when the difference was in the range 0.6 × 1012 to 0.9 × 1012 molecules cm–3
A classification of synoptic patterns inducing heavy precipitation in Saudi Arabia during the period 2000-2014
Get PDFThis study investigates the synoptic patterns associated with the development of heavy rainfall in five different regions of Saudi Arabia. Different synoptic patterns were derived for the heavy rainfall events using a correlation-based map of pattern classifications applied to 1000 hPa gridded NCEP/UCAR reanalysis data for the period 2000-2014. The study summarizes six major synoptic features and classifies 28 detailed synoptic patterns emerging from 186 cases. The derived synoptic patterns differ significantly at lower levels but are relatively similar at upper levels. Heavy rainfall events were most frequent in winter and then spring, while a small percentage occurred during fall in all the regions of the country. In summer, heavy precipitation was restricted to the southern region, which is influenced by an upslope flow
Influence of initial soil moisture and vegetation conditions on monsoon precipitation events in northwest México
Get PDFLand surface conditions including soil moisture and vegetation states are expected to play important roles in the development of the daytime boundary layer and the formation of convective precipitation. For areas with an in-phase seasonality of radiation and precipitation, such as the North American Monsoon (NAM) region, diagnosing the direct contributions of each effect is difficult given the co-occurrence of high soil moisture and vegetation greening during the warm season. In this study, we use the WRF-Hydro modeling system to simulate the interactions between the land surface and atmosphere within a large watershed in northwest México subject to the influence of the NAM. After testing the coupled simulations against a bias-corrected reanalysis product for two summer periods in 2004 and 2013, we conduct a series of storm-scale modeling experiments that separately vary the initial soil moisture and vegetation conditions. Results reveal that both soil moisture and vegetation anomalies can positively affect convective precipitation, although their influence on boundary layer development is different. We then diagnose the specific land-atmosphere mechanisms by which the land surface states positively influence convective precipitation. Under high land surface anomalies, such as initial soil moisture equal to field capacity or the maximum vegetation greening state, storm-scale (48 h) precipitation accumulations can be increased up to 26 mm. As a result, improvements in how land surface conditions are initialized either through remote sensing or sensor networks are critical for enhancing precipitation prediction systems in the NAM region