Atmósfera (Journal)
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Thermodynamic simulation of the seasonal cycle of temperature, pressure and ice caps on Mars
Get PDFWe present a thermodynamic model to simulate the atmospheric temperature and pressure, the regolith temperature and the polar CO2 ice caps vertical thickness and horizontal extent of Mars. This is done using the temperatures of the atmosphere and regolith for each Martian day of the year, determined from the thermodynamic equation. Assuming a CO2 atmosphere, we calculate its emission spectrum using the spectral calculator E-Trans with the HITRAN database (E-Trans/HITRAN), resulting in only a band at 15 mm and the rest transparent, through which the radiation emitted by the regolith and ice caps (considered as black bodies) goes toward space. We also include the solar radiation extinction and longwave emission of atmospheric dust. The equation calculates the energy balance between the absorbed solar radiation and the outgoing longwave radiation, incorporating also the latent heat released by CO2 condensation, the sensible heat flux from the surface to the atmosphere, the latent heat flux due to the CO2 ice sublimation and the heat exchange between the surface regolith layer and its lower layers. The atmospheric planetary scale horizontal turbulent heat transport is parameterized with an exchange coefficient, which is an order of magnitude smaller than that employed in the terrestrial troposphere. Considering a long-time average, the regolith vertical temperature profile is explicitly found using the thermal inertia including conductivity; its temperature regulation is achieved through the thermal conduction from the surface during the warm season. This stored energy goes back to the surface during the cold season. Our model simulates the seasonal variation of the polar ice caps and consequently of the surface atmospheric pressure through the CO2 mass balance between them. Finally, it is explicitly shown that the amplitude of the global seasonal pressure cycle is modulated by a local thermal-orographic effect, which increases (decreases) this amplitude in the low (high) regions, which agrees with the observations of the Viking Landers 1 and 2, and the Mars Climate Data Base. Our prediction for Hellas Planitia gives an amplification factor of up to 2.15, coinciding with other authors
Seasonal trend analysis of carbon dioxide across latitudes of Africa, Europe and Asia
Get PDFCarbon-driven emissions are on the rise and much work remains to be done to benchmark seasonal carbon increase and ensure its prompt reduction. There is a great need of new methods for validating seasonal trends of carbon dioxide (CO2). We obtained CO2, temperature and normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Terra satellite from 2003 to 2008 over Africa (Nigeria, Mauritania, Congo, Sudan), Europe (France, Finland, Turkey, Ukraine), and Asia (China, Mongolia, India, Afghanistan). For the first time, seasonal index analysis was used to validate vegetation index. The seasonality in carbon dioxide was determined dividing the monthly average by the annual mean. Additionally, the percentage difference correlation of the NDVI and CO2 relationship was calculated to investigate the underlying influence of both parameters and validate the seasonal change resulting from the solar activity cycle. By grouping years based on solar activity maximum (2003-2004), intermediate (2005-2006) and very low activity (2007-2008), the results expanded the physical interpretation that seasonal fluctuation of NDVI corresponds to the terrestrial sink of regional CO2, mostly occurring during equinoctial months. Our results demonstrate that seasonal variation of CO2 depends on geographic latitude and the solar activity cycle. This result is essential in studying the future trend relationship between NDVI and CO2
Evaluation and calibration of downward longwave radiation models under cloudless sky at Ile-Ife, Nigeria
Get PDFDownward longwave radiation flux is an important variable for estimating net radiation, in order to investigate the surface energy budget and carry out climatic studies. The flux is usually estimated using empirical models based on the information of meteorological parameters such as relative humidity, surface and air temperature, and water vapor pressure. This paper presents the assessment of 11 widely used empirical models for estimating downward longwave radiation using a ground-based dataset acquired from January 2016 to December 2017 at Ile-Ife, a tropical city in Nigeria. The original Idso and Niemela et al. models performed better than other models with errors less than 5.0% when compared to measured values. The performances of all the models improved greatly after calibration. The Guest model, which gave low errors (MBE = 0.65 Wm–2, RMBE = 0.15%, RMSE = 9.38 Wm–2, RRMSE = 2.14%, MAE = 7.84 Wm–2, RMAE = 1.79%), performed best followed by the Dilley and O’Brien, Idso, Prata, Brutsaert, Garratt, Niemela et al., and Ångström models. The calibrated models presented in this study can be used to estimate the flux under cloudless sky conditions at Ile-Ife and at other places with similar meteorological conditions, where this flux is not measured due to technological problems and the high cost of purchasing and maintaining the needed sensors. The proposed model for estimating the flux showed better performance with lower statistical errors than all the existing empirical models tested, and conform greatly (R2 = 0.88) to the measured data
Evaluation of clearness index and cloudiness index using measured global solar radiation data: A case study for a tropical climatic region of Nigeria
Get PDFThis study uses a two-year dataset (January 2016-December 2017) on global solar radiation to model the clearness and cloudiness indices at Ile-Ife, Nigeria, a tropical location. Analysis of the daily variations showed that most days at the location are uniform in cloudiness, with scarcely any day either extremely cloudy or extremely clear. On a monthly basis, the clearness index ranged from 0.27 to 0.51, while cloudiness index ranged from 0.44 to 0.72, confirming that the variations of both ratios are influenced by changes in the position of the sun, turbidity and clouds. The seasonal variations of the two parameters were observed to be inverse, so that increases in the clearness index induced by cloudless sky and dry months correspond to decreases in the cloudiness index values and vice versa. The minimum values (0.10 and 0.28) of the clearness index at the location are observed to be higher than the minimum value of 0.05 stipulated for the clearness index in cloudy conditions. Two empirical equations for estimating the maximum clearness index in terms of the average clearness index and the cloudiness index in terms of the clearness index are developed and recommended for other locations with climatological conditions similar to those of the study site. It was furthermore observed from the evaluation of formulated empirical equations that the Hollands and Huget and the Saunier et al. models performed well and improved by about 23.62 and 3.66%, respectively, after calibration, to make the models suitable for their application at other tropical areas.
Optical properties of atmospheric aerosol over Cape Town, Western Cape of South Africa: Role of biomass burning
Get PDFThe optical characteristics of atmospheric aerosol are vital in the determination of regional climate trends. Biomass burning is typically known to influence aerosol optical characteristics. Following the incessant biomass burning and the recent drop in precipitation over Western Cape, aerosol optical properties with a focus on the impact of biomass burning are studied over Cape Town using data from the Aerosol Robotic Network (AERONET) and the Moderate Resolution Imaging Spectroradiometer (MODIS). In general terms, measurements from both platforms significantly agree on the estimates of aerosol optical depth (AOD) and water vapor content. The mean AOD (0.075 ± 0.022) and the Ångström exponent (0.63 ± 0.19) derived from AERONET demonstrate the dominance of coarse mode aerosol typical of maritime aerosol. Similarly, aerosol particle size distributions display the predominance of coarse mode particles. However, the derived refractive index is more representative of urban-industrial aerosol. Also, estimated back-trajectories show that more than 70% of the aerosol particles over the region originate over the ocean. Atmospheric vapor increases from winter to summer, mainly influenced by air temperature, supersaturation level, and absorbing aerosol. Furthermore, two significant sources accounted for biomass burning related to high AOD values: local biomass burning and regionally transported aged smoke majorly from elsewhere in Sothern Africa
Low-level windshear associated with atmospheric boundary layer jets – Case studies
Get PDFJet streams in the atmospheric boundary layer may lead to hazardous weather over southern China. In this paper, the jet-related low-level windshear to be encountered by an aircraft is documented. Two typical cases under the northeast monsoon regime are considered, namely, easterly jet disrupted by the mountains to the south of Hong Kong International Airport, and outbreak of monsoon surge that produces a low-level northeasterly jet. The Doppler Light Detection and Ranging (LIDAR) systems are found to capture the corresponding windshear features very well, e.g., consistent with pilot reports and flight data. They are useful in providing timely alert to the aircraft. In particular, the LIDAR captures a double jet structure in the atmospheric boundary layer for the easterly wind case, which has not been reported in the literature before. The physical mechanism for the occurrence of the double jet is yet to be revealed. Moreover, the performance of a high spatial resolution (200 m) numerical weather prediction (NWP) model in predicting the jet and the associated low-level windshear is studied. The model is found to provide reasonable prediction of the windshear features at a few hours ahead, and, for the cases studied, shows skills in providing timely alerts to the aircraft
Spatial and temporal characteristics of four main types of meteorological disasters in East China
Get PDFBased on the disaster census data of four types of meteorological disasters (floods induced by rainstorms, droughts, damages due to low temperatures and high temperatures and heat waves) in 637 counties (districts) of East China, the spatial distribution and inter-annual variation in the number of records and the amount of impacts or losses caused by the four types of disasters were analyzed. The results indicate that rainstorm-induced flood disasters had the largest number of records and the largest affected population, death population, affected crop, total crop failure and direct economic loss in East China. The yearly percentage of affected population and direct economic loss caused by the four types of meteorological disasters increased significantly at rates of 1.4 and 2.2% per decade, respectively, but the deaths decreased significantly at a rate of 2.2% per decade during 1984-2010. There was no statistical significance in the percentage change of affected crop area and total crop failure area in East China. Spatially, the total number of people affected by the four types of meteorological disasters was higher in Anhui and Jiangxi, and the deaths were more in southern Anhui, Jiangxi, Zhejiang, and Fujian. Both the affected area and the total failure area of crops were higher in northern Anhui, eastern Jiangsu and eastern Shandong, and the direct economic losses were higher in the southern part of East China and Anhui province
Implications of 1.5 and 2.0 ºC additional warming for wheat yield using a gridded modeling approach
Get PDFThe goal of limiting the increasing global mean temperature below 2.0 and possibly 1.5 ºC, was decided in the Paris Agreement of 2015. It is therefore important to understand the climate risk and impacts associated with 1.5 and 2.0 ºC additional warming scenarios. The current study investigates the impacts of 1.5 and 2.0 ºC additional warming on wheat yield in Pakistan using a gridded modeling approach. The generated climate data by four GCMs under 1.5 and 2.0 ºC were acquired from the Half a Degree Additional Warming, Prognosis and Projected Impacts (HAPPI) scenarios group. The CERES-Wheat model was calibrated and evaluated using field data and then applied to the entire region of Pakistan. Model calibration results showed a close association between observed and simulated wheat yield with an error ranging from 0.52 to 1.36%. Climate change projections indicated that the mean temperature is expected to rise by 0.46 and 1.44 ºC in the 1.5 and 2.0 ºC additional warming scenarios in the GCMs, respectively. The spatial variations of precipitation range from –22.4 to 42.6% and 4.6 to 34.1% under the 1.5 and 2.0 ºC HAPPI scenarios, respectively. Higher precipitation was recorded in northern Pakistan as compared to central and southern Pakistan. The projected changes in temperature and precipitation will decrease the wheat yield by 3.2 and 4.7% in Punjab, 17.8% and 13.8% in Sindh province under 1.5 and 2.0 ºC additional warming, respectively. However, the wheat yield will increase by 4.7 and 13% in Khyber Pakhtunkhwa and 9.4 and 15.3% in Baluchistan under 1.5 and 2.0 ºC additional warming, respectively
Crop yield simulations in Mexican agriculture for climate change adaptation
Get PDFClimate change is considered a serious threat to food security worldwide. In this study, yields of maize, beans, wheat, soybean, sorghum, barley and potato were modeled with 28 future climate change scenarios. Our results reduce the information gap that is frequently reported for Mexico and will contribute to better knowledge on spatial impact of climate change. We applied FAO AquaCrop model for 22 case studies located in 14 states of Mexico. Climate change scenarios were: CNRM, GFDL, HADGEM, MPI and Ensemble REA, with two radiative forcing concentrations (4.5 and 8.5 W m–2) and three time horizons (2015-2039, 2045-2069, and 2075-2099). The results show decreases in yields of most of the case studies as a consequence of a decrease in the amount and distribution of precipitation. Maize yield in warm dry climates could decrease up to 84% in the most severe scenarios. Beans could decrease from 10 to 40% in the north of the country, while in the northwest a 15% decrease in wheat yield is predicted. Soybeans could benefit, with increases from 15 to 40%. Sorghum and potatoes are expected to decrease for all the case studies, while barley would have increases and decreases. The results suggest differentiated impacts according to crops and regions studied. We concluded that agriculture requires better focused strategies and policies (attention on crop and spatial distribution)
Potential sources and measured concentrations of VOCs in Balikesir ambient atmosphere
Get PDFThe assessment of volatile organic compounds (VOCs) has become an important field of interest in atmospheric pollution. This study quantifies and characterizes the ambient levels and spatial distribution of VOCs in urban and rural areas of Balikesir city, Turkey. For these assessments, passive sampling of VOCs performed at approximately 50 locations in and around the city of Balikesir. Twenty-five VOCs were regularly monitored and analyzed with the GC-FID system. The sampling periods were carried out for seven-day periods during March and August 2010. In the study, mean ∑VOC concentrations were found to be as high 67 and 51 µg m–3 for the winter and summer seasons, respectively. Median concentrations of benzene, toluene, ethylbenzene, m,p-xylene and o-xylene were 2.6, 11, 1.30, 1.80 and 0.73 μg m-3, respectively. Although there were some changes between concentrations of VOC groups between the summer and winter campaigns, differences were not dramatic. Winter-to-summer ratios of the target compounds ranged from 0.2 (1,2,4-trimethylbenzene) to 9 (hexane). Most of the target compounds have higher concentrations in winter. Only few VOCs, including n-propylbenzene, 1,2,4- trimethylbenzene, 1-undecene and 1,2,4- trichlorobenzene have higher concentrations in summer. Spatial distribution of VOCs demonstrated that the roads are hot spots for measured VOC concentrations. The drinking water treatment plant, industrial solvent emissions from pesticide and insecticide applications in agriculture, and emissions from traffic were the sources that contribute to total VOC load in the Balikesir atmosphere