Atmospheric black carbon concentrations in Mexico Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Oscar Peralta, Abraham Ortínez-Alvarez, Roberto Basaldud, Naxieli Santiago, Harry Alvarez-Ospina, Karen de la Cruz, Valter Barrera, María de la Luz Espinosa, Isabel Saavedra, Telma Castro, Amparo Martínez-Arroyo, Víctor H. Páramo, Luis G. Ruíz-Suárez, Felipe A. Vazquez-Galvez, Arturo Gavilán Abstract Atmospheric black carbon concentrations were measured at two urban sites (Mexico City and Monterrey), one suburban site (Juriquilla) and one high-altitude site (Altzomoni) in Mexico during 2015 and part of 2016. Black carbon concentrations were compared against other criteria gases finding a strong correlation with carbon monoxide at the urban sites. The carbon monoxide-black carbon correlation for the Mexico City site is 0.77. Urban sites had an average black carbon concentration of above 2.5 μg m−3, the suburban site 0.75 μg m−3, and the high-altitude site 0.27 μg m−3. Compared to other studies, the average levels are comparable, and the urban and suburban locations showed a trend towards increased atmospheric black carbon concentrations at year end. Other urban places (Guadalajara, Cuernavaca, and Iztapalapa) reported black carbon concentrations, but for less than a year. For the first time, a Latin-American country (Mexico) measured black carbon continuously at several sites for a year applying the same data quality assurance.

Implementation of a novel seeding material (NaCl/TiO2) for precipitation enhancement in WRF: Description of the model and spatiotemporal window tests Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Mladjen Ćurić, Miloš Lompar, Djordje Romanic Abstract Precipitation enhancement might play a key role in combating constantly increasing frequency of occurrence of draughts in many areas around the globe. This article is a numerical study of the performances of two precipitation enhancers using seven different spatiotemporal windows. The investigated artificial aerosols are the pure NaCl—being a well-researched seeding material—and the core/shell NaCl/TiO2 (abbreviated as CSNT)—being a novel seeding material very recently developed. The activation properties of CSNT are for the first time incorporated into the Weather Research and Forecasting (WRF) model. The performances of two seeding materials, as well as their benchmark against the control case without seeding are investigated in terms of the accumulated surface precipitation and cloud microphysics processes. This study shows multiple advantages of the new seeding agent in terms of both the total accumulated surface precipitation and the increased precipitation area. The best location for release of CSNT in terms of the highest increase of precipitation amount is when both cyclonic and anticyclonic cells are seeded. The largest increase of precipitation area is found when the seeding takes place in front of the cloud and below the cloud base. In this case, the seeded cloud with CSNT releases precipitation over approximately 2 times larger area that the unseeded cloud. The conducted numerical experiments showed that the introduction of CSNT into the cloud environment significantly increases the number concentration of cloud droplets and ice.

Secondary organic aerosol formation from α-methylstyrene atmospheric degradation: Role of NOx level, relative humidity and inorganic seed aerosol Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Mercedes Tajuelo, Ana Rodríguez, María Teresa Baeza-Romero, Alfonso Aranda, Yolanda Díaz-de-Mera, Diana Rodríguez Abstract Secondary Organic Aerosol (SOA) formation during the photolysis and OH-photooxidation of α-methylstyrene was investigated using a simulation chamber at atmospheric pressure and room temperature (296 ± 1) K. α-Methylstyrene concentration was followed by gas chromatography with a mass spectrometric detector (GC–MS) and the aerosol production was monitored using a Fast Mobility Particle Sizer (FMPS). The effect of varying α-methylstyrene (0.5 ppm - 2 ppm) and NOx (0.5 ppm - 1.0 ppm) concentrations on SOA formation was explored, as was the effect of the relative humidity (RH) (5–50%) and the presence of inorganic seed particles. Results indicate that SOA yields increase at higher α-methylstyrene concentrations; low NOx and high RH conditions favour more rapid aerosol formation and a higher aerosol yield; SOA formation is independent of seed surface area, within the studied range, for both inorganic seed particles ((NH4)2SO4 and CaCl2). An off-line chemical analysis using a filter/denuder sampling system and GC–MS confirms acetophenone as the main gas phase product in both processes, photolysis and photooxidation. For the first time, SOA composition in α-methylstyrene degradation was analysed, observing acetophenone and acetol as products present in the formed aerosol in presence and absence of NOx.

Estimating the response of hydrological regimes to future projections of precipitation and temperature over the upper Yangtze River Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Xiaoli Yang, Xiaohan Yu, Yuqian Wang, Yi Liu, Mengru Zhang, Liliang Ren, Fei Yuan, Shanhu Jiang Abstract The upper region of the Yangtze River, as the freshwater source for the middle and lower Yangtze River, is highly vulnerable to climate change. Understanding and projecting the spatiotemporal variability of extreme flows in this region are key to creating appropriate adaptation policies and strategies. In this study, climate change signals were scaled from seven bias-corrected CMIP5 models and were used to force a variable infiltration capacity (VIC) model to quantify and assess the impact of climate change on the hydrology of the region. The respective contribution of precipitation (P) and temperature (T) to evapotranspiration (ET) and hydrological regimes (annual mean runoff, high flow, and low flow) were also quantified using the analysis of variance method (ANOVA). For the scenario period (2031–2060), the projected runoff is projected to increase in vary between 11.33% and 64.08% in winter, while increases in summer range from 8.64% to 40.97%. The changes in ET are different depending on the climate mode used; these increase during winter and decrease in summer under the influence of temperature. In addition, we found that low flows are projected to decrease while the mean annual runoff will increase in the future period. These projected changes demonstrated that temperature effects dominate in the study area for the future period under the representative concentration pathway 8.5 scenario.

Analysis of the atmospheric circulation pattern effects over SPEI drought index in Spain Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Antonio Manzano, Miguel A. Clemente, Ana Morata, M. Yolanda Luna, Santiago Beguería, Sergio M. Vicente-Serrano, M. Luisa Martín Abstract Drought episodes affect large continental areas all over the world, becoming one of the main natural hazards regarding their economic, social and environmental impacts. The design and improvement of drought monitoring and forecasting systems has become a priority application and has driven the need to a better understanding of the development of drought episodes. In this work, a study of the relationships between drought conditions over the Iberian Peninsula and teleconnection patterns with a major impact over this region is assessed. The three-month aggregated standardized precipitation evapotranspiration index (SPEI) is used to characterize different clustered areas with homogeneous hydrological behaviour on a seasonal basis. Correlation results reveal that Artic Oscillation (AO) and North Atlantic Oscillation (NAO) patterns have a significant impact on droughts in winter over large areas of the Iberian Peninsula, while the Western Mediterranean Oscillation (WeMO) pattern exhibit the largest influence on hydrological behaviour over the southeastern region. The East Atlantic (EA) pattern effects switch between weakening and reinforcement as result of a balance of two different processes such as the increase in precipitation (dominant in winter) and the increase in temperature (dominant in summer). A wavelet analysis is performed to the seasonal mean atmospheric pattern time series and clustered mean SPEI time series. The wavelet power spectra highlight common periodicity features pointing out the close relationships between the atmospheric patterns and the drought index.

Symmetrical uncertainty and random forest for the evaluation of gridded precipitation and temperature data Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Mohamed Salem Nashwan, Shamsuddin Shahid Abstract Selection of appropriate gridded rainfall and temperature data is a key problem for hydro-climatic studies, particularly in regions where long-term reliable and dense observations are not available. The ability of two intelligent algorithms, symmetrical uncertainty (SU) and random forest (RF), to assess the degree of similarity or the distance between two time series was utilized in this study for the evaluation of gridded climate data. In this study, the performances of seven widely used gridded rainfall datasets and five temperature datasets were evaluated against the available station data in Egypt. Monthly rainfall and mean temperature data recorded at 57 locations for the period 1979–2014 were used for this purpose. The results revealed the better performance of Global Precipitation Climatology Centre (GPCC) gridded rainfall and University of Delaware (Udel) gridded temperature data in replicating observed rainfall and mean temperature, respectively, in most of the locations in Egypt. Validation of the results using conventional statistical metrics revealed the better performance of different datasets in term of different metrics at different locations. However, the mean values of all the metrics support the results obtained using SU and RF. The study indicates that SU and RF can be used for the selection of appropriate gridded rainfall and temperature data by avoiding confusion arise from contradictory results obtained using various statistical metrics.

Evaluation and comparison of CHIRPS and MSWEP daily-precipitation products in the Qinghai-Tibet Plateau during the period of 1981–2015 Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Jun Liu, Donghui Shangguan, Shiyin Liu, Yongjian Ding, Shaoping Wang, Xiuna Wang Abstract High-resolution, long-term and accurate daily-precipitation is always difficult and rarely measured in the Qinghai-Tibet Plateau (QTP) because of the high altitude and complex terrain. The accuracy of satellite-based gridded precipitation products have been continuously improved recently which is crucial to the study of cryosphere ecology and environment. The goal of this study is to evaluate the accuracy of CHIRPS v2 (Climate Hazards Group Infrared Precipitation with Stations data, version 2) and MSWEP v2 (Multi-source weighted-Ensemble Precipitation, version 2) daily-precipitation products over the QTP during the period 1981–2015. Validation was done using a time series of daily-precipitation data obtained from 104 hydrometeorological stations distributed over the QTP. Error metrics (The correlation coefficient CC, the relative bias BIAS, and root mean square error RMSE) were used for accuracy evaluation and detectability indicators (probability of detection POD, false alarm ratio RFA, and critical success index CSI) were used for the analysis of detection capabilities of rainfall occurrence events. The results indicate that when compared to rain gauge observations, CHIRPS and MSWEP daily-precipitation products represent well the spatial and temporal distribution of the mean daily precipitation over the QTP, while both of them overestimate the daily-precipitation (0.18 mm/d for CHIRPS, 0.56 mm/d for MSWEP). MSWEP performed better than CHIRPS according to CC (MSWEP is 0.44, CHIRPS is 0.23) and RMSE (MSWEP is 4.21 mm, CHIRPS is 5.03 mm) and MSWEP showed better detection capabilities with higher POD (0.65), lower RFA (0.50) and higher CSI (0.39) in the QTP. Both products are less accurate in dry conditions (the north QTP, winter) than in moist conditions (the south QTP, summer). Light precipitation events (0–2 mm/d) are underestimated but heavy precipitation events (2–25 mm/d) are overestimated. CHIRPS and MSWEP have shown great potential to be able to be applied to the precipitation-related study of the QTP. Although the accuracy of MSWEP is higher than that of CHIRPS, the latter has higher spatial resolution (o.o5°) and is more suitable for small-scale studies.

Evaluation of retrieved aerosol extinction profiles using as reference the aerosol optical depth differences between various heights Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): M. Herreras, R. Román, A. Cazorla, C. Toledano, H. Lyamani, B. Torres, V.E. Cachorro, F.J. Olmo, L. Alados-Arboledas, A.M. de Frutos Abstract Aerosol extinction vertical profiles at Granada (Spain) are calculated with the GRASP (Generalized Retrieval of Aerosol and Surface Properties) code using as input Aerosol Optical Depth (AOD) and sky radiance measurements from AERONET (AEerosol RObotic NETwork) and ceilometer RCS (Range Corrected Signal) profiles, both corresponding to the Granada (Spain) station. This methodology is so called GRASPpac due to the combination of sun/sky photometer and ceilometer on GRASP. In order to evaluate the accuracy of these retrieved extinction profiles at Granada, two more nearby AERONET stations, located at different altitudes, are used. The AOD difference of the three choosen AERONET sun/sky photometers have been used to calculate the Integrated Aerosol Extinction (IAE) at different height layers. These three AERONET sun/sky photometers are used as a reference and compared against the integrated extinction at the same layers from the extinction profiles retrieved by GRASPpac. The differences between AERONET and GRASPpac retrieved IAE values indicate that GRASPpac aerosol extinction profiles are at least within the uncertainty of the sun/sky photometer measurements, but GRASPpac method overestimates the AERONET extinction at low altitudes and underestimates it at high levels. The most accurate and precise retrieved extinction correspond to the intermediate layer with a mean bias error (MBE ± standard deviation) of 0.00 ± 0.01 (0 ± 59%) for 1020 nm, and the worst integrated extinction results were obtained for the upper layers with a MBE of −0.01 ± 0.02 (28 ± 36%) for 1020 nm. In general these MBE values increases for shorter wavelengths. In order to obtain a complete characterization of this bias, the dependence of the obtained differences on the aerosol size and the solar zenith angle, among others, are analysed in detail. Finally, the behaviour of vertically-resolved aerosol extinction at Granada is evaluated using averages of the retrieved profiles from November of 2012 to December of 2017. The highest IAE values are found in Summer with mean values of 0.09 for the lower layers and 0.07 for the upper ones, both at 440 nm wavelength.

Recent climate trends over Greece Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Chris G. Tzanis, Ioannis Koutsogiannis, Kostas Philippopoulos, Despina Deligiorgi Abstract Temperature and humidity play a key role in climate change assessment. This study focuses on the analysis of surface and upper-air temperature and humidity trends for a domain centered over the Greek region in the Eastern Mediterranean. The main purpose of this work is to investigate whether possible changes in the climate of the greater Greek region exist over the recent years. ERA-Interim reanalysis, surface and radiosonde observational data of air temperature, specific and relative humidity are used for a 39-year period (1979–2017). Through the spatial distribution of their trends, at different atmospheric pressure levels and seasons, it is possible to detect statistically significant spatial and temporal changes in the troposphere and stratosphere above the examined domain. Statistically significant warming trends at the 99% level are found at the surface over land and at the 95% level over sea during spring and summer for Greece; less pronounced and more sparsely distributed trends are identified during autumn and winter. Additionally, positive trends prevail throughout the entire extent of the troposphere, more pronounced during summer, whereas the stratosphere is characterized by negative trends. Trends derived from the reanalysis and observational data exhibit high degree of correlation both at surface and at upper atmospheric levels. In accordance, specific humidity has generally increased in the lower troposphere. Relative humidity time series demonstrate trends, which vary seasonally and geographically, due to its relationship with specific humidity and temperature.

Effect of momentum control variables on assimilating radar observations for the analysis and forecast for Typhoon Chanthu (2010) Publication date: 1 December 2019 Source: Atmospheric Research, Volume 230 Author(s): Feifei Shen, Dongmei Xu, Jinzhong Min Abstract The background error covariance is a vital component in data assimilation systems, which is usually simplified with the control variable preconditioning procedure. This study aims to assess the impact of the determination of the momentum control variables using ψ and χ (CV_ψχ) or direct x and y components of wind(CV_UV)on the analysis and forecast of a typhoon case for Doppler radar radial velocity (Vr) data assimilation. It is shown that using direct U-wind and V-wind as the control variables is able to reflect the observed wind itself more objectively. Smaller scale increment is found with the use of CV_UV, which is more physical compared to CV_ψχ. Generally, CV_UV yields smaller wind analysis error than CV_ψχ. The vertical structure from CV_UV are more accurate than that from CV_ψχ with enhanced vortex circulation and warm core. The subsequent composite reflectivity, track and intensity forecast using the CV_UV is improved over that using CV_ψχ, due to more accurate wind field that lead to correct convergence for the typhoon system. Sensitivity experiments of the temporal frequency of DA under the determination of the momentum control variable pairs are also conducted. The results show that there are also no clear, positive impacts of increasing the DA frequency on the forecasts especially for the CV_UV experiment.