Meteorological Regimes Research Articles

Clustering Surface Ozone Diurnal Cycles to Understand the Impact of Circulation Patterns in Houston, TX

AbstractThe diurnal cycle of surface ozone is directly influenced by the chemistry and meteorological processes which affect a region. This study uniquely employs a clustering methodology to examine the complete diurnal pattern of surface ozone for the Houston‐Galveston‐Brazoria region and links the identified patterns to meteorological regimes for June, July, and August of 3 years (2011, 2014, and 2015). Four features were implemented into the clustering algorithm: ozone rate of decrease at night, daily minimum before sunrise, rate of increase after sunrise, and an average of afternoon ozone. Four clusters were chosen, ranging from a mostly flat diurnal pattern with low mixing ratios (~20 ppbv) throughout the day (Cluster 1), to a more variable diurnal cycle with very high mixing ratios (>70 ppbv) in the afternoon (Cluster 4). The clusters are found to associate with distinctive circulation patterns and well‐known regional meteorological processes, such as the low‐level jet and Bermuda High. The uneven distribution of the clusters between the years helps elucidate ozone interannual variability due to meteorology: Cluster 4 had 0 days assigned from 2014 due to the greater influence of circulation patterns bringing clean air from the Gulf of Mexico. We show that the clustering method better characterizes ozone variability than the simplistic method of dividing peak ozone into quantiles. With the clustering analysis, we demonstrate that the ozone diurnal pattern holds more value than just peak ozone hours of the day in providing a clearer understanding of ozone variability and associated meteorological processes.

Meteorological regime of the glacier No. 18 (the Peak Topografov massiv, East Sayan range)

For the first time, experimental data on the meteorological regime of a continental glacier (No. 18, East Sayan range, south of East Siberia) have been obtained during the summer seasons of 2015–2017. Standard meteorological parameters, such as air temperature, humidity, atmospheric pressure, precipitation, incoming short-wave solar radiation, wind speed, and wind direction were measured by using the automatic weather station installed at the lower part of the accumulation area of the glacier (at elevation 2, 550 m). It was established that the meteorological regime of the glacier is characterized by a relatively high mean daily temperatures, humidity and cloudiness, while mean wind speed is relatively low. Liquid precipitation dominates over the solid one and condensation over evaporation. It has been found that temperature and precipitation time series on the glacier correlate well with those at the nearest weather station Orlik and NCEP/NCAR reanalysis data. The main energy sources for snow/ice melting have been estimated and the main contribution to glacier ablation has been attributed to net shortwave radiation.

Using Short‐Term CO/CO2 Ratios to Assess Air Mass Differences Over the Korean Peninsula During KORUS‐AQ

AbstractOne‐second in situ measurements of CO and CO2 mole fractions were made aboard the National Aeronautics and Space Administration DC‐8 aircraft during the 2016 KORUS‐AQ joint air quality and atmospheric chemistry field campaign in South Korea. The ratio of CO to CO2 enhancement is used to characterize regional combustion source signatures. Calculations of the ∆CO/∆CO2 ratio were made with a short duration rolling window (60 s), filtered by the coefficient of determination (R2), and plotted as distributions to characterize air masses measured from the aircraft during the campaign. The KORUS‐AQ sampling domain was divided into analysis regions to facilitate the analysis. Over Seoul, the boundary layer shows a low‐ratio signature in the ∆CO/∆CO2 ratios, with more than 50% of the correlated slopes in the boundary layer falling below 1% ∆CO/∆CO2, and 80% of the slopes between 0% and 2% ∆CO/∆CO2. However, this behavior changes to a larger ratio distribution at higher altitudes. The West Sea receptor region was divided into three analysis sectors, by meteorological regime, and used in conjunction with measurements collected over China during the KORUS‐AQ campaign time period to characterize the Chinese ∆CO/∆CO2 ratio signature. Chinese‐type emissions have a slope distribution that is shifted to higher ratios and broadened compared to measurements over Seoul, with the bulk of the measurements between 2% and 4% ∆CO/∆CO2, with few negative slopes. The measured ratio trends over South Korea are consistent with inventoried CO and CO2 emissions.

Control of seasonal water vapor isotope variations at Lhasa, southern Tibetan Plateau

Water isotopes in precipitation provide new insight on the controlling factors for moisture source variations on the Tibetan Plateau. However, understanding the intra-annual water isotope cycle is difficult for a region lack of winter precipitation. Here, we reported water vapor δ18O and δ2H time series over two and half years at Lhasa on the southern Tibetan Plateau. We compare our values with concurrent daily precipitation isotopes to assess the seasonal controls of vapor isotopes and possible correlation to precipitation isotopes. Results show an intra-seasonal dependence of water vapor δ18O on large scale meteorological regime. During the winter months, vapor water δ18O shows positive dependence on regional-scale temperature, confirming a Rayleigh-distillation controlling moisture transport. During the summer months, lower vapor δ18O is weekly in association with the heavy precipitation over tropical Indian Ocean and on the Tibetan Plateau, and this relation is further enhanced by the evaporation of precipitation at the sampling site. We also found a weak seasonal variation of vapor d-excess, likely resulted from climate seasonality over the large moisture sources region. Moreover, the isotope dataset contains a high-frequency of fluctuations for both δ18O and d-excess lasting several days during the summer monsoon season. These high frequency fluctuations are in phase with precipitation events, confirming significant local evaporation effects on the short-term water cycle, which further complicated the control of near surface water vapor isotopes. These findings improve our regional scale understanding of hydrological cycle on the southern Tibetan Plateau, and will potentially improve our understanding of isotope variations in proxy archives in the Tibetan Plateau.

Satellite inference of water vapour and above-cloud aerosol combined effect on radiative budget and cloud-top processes in the southeastern Atlantic Ocean

Abstract. Aerosols have a direct effect on the Earth's radiative budget and can also affect cloud development and lifetime, and the aerosols above clouds (AAC) are particularly associated with high uncertainties in global climate models. Therefore, it is a prerequisite to improve the description and understanding of these situations. During the austral winter, large loadings of biomass burning aerosols originating from fires in the southern African subcontinent are lifted and transported westwards, across the southeastern Atlantic Ocean. The negligible wet scavenging of these absorbing aerosols leads to a near-persistent smoke layer above one of the largest stratocumulus cloud decks on the planet. Therefore, the southeastern Atlantic region is a very important area for studying the impact of above-cloud absorbing aerosols, their radiative forcing and their possible effects on clouds. In this study we aim to analyse and quantify the effect of smoke loadings on cloud properties using a synergy of different remote sensing techniques from A-Train retrievals (methods based on the passive instruments POLDER and MODIS and the operational method of the spaceborne lidar CALIOP), collocated with ERA-Interim re-analysis meteorological profiles. To analyse the possible mechanisms of AAC effects on cloud properties, we developed a high and low aerosol loading approach, which consists in evaluating the change in radiative quantities (i.e. cloud-top cooling, heating rate vertical profiles) and cloud properties with the smoke loading. During this analysis, we account for the variation in the meteorological conditions over our sample area by selecting the months associated with one meteorological regime (June–August). The results show that the region we focus on is primarily under the energetic influence of absorbing aerosols, leading to a significant positive shortwave direct effect at the top of the atmosphere. For larger loads of AACs, clouds are optically thicker, with an increase in liquid water path of 20 g m−2 and lower cloud-top altitudes by 100 m. These results do not contradict the semi-direct effect of above-cloud aerosols, explored in previous studies. Furthermore, we observe a strong covariance between the aerosol and the water vapour loadings, which has to be accounted for. A detailed analysis of the heating rate profiles shows that within the smoke layer, the absorbing aerosols are 90 % responsible for warming the ambient air by approximately 5.7 K d−1. The accompanying water vapour, however, has a longwave effect at distance on the cloud top, reducing its cooling by approximately 4.7 K d−1 (equivalent to 7 %). We infer that this decreased cloud-top cooling in particular, in addition with the higher humidity above the clouds, might modify the cloud-top entrainment rate and its effect, leading to thicker clouds. Therefore, smoke (the combination of aerosol and water vapour) events would have the potential to modify and probably reinforce the underlaying cloud cover.

Evaluation of the effect of regional joint-control measures on changing photochemical transformation: a comprehensive study of the optimization scenario analysis

Abstract. Heavy haze usually occurs in winter in eastern China. To control the severe air pollution during the season, comprehensive regional joint-control strategies were implemented throughout a campaign. To evaluate the effectiveness of these strategies and to provide some insights into strengthening the regional joint-control mechanism, the influence of control measures on levels of air pollution was estimated with an integrated measurement-emission-modeling method. To determine the influence of meteorological conditions, and the control measures on the air quality, in a comprehensive study, the 2nd World Internet Conference was held during 16–18 December 2015 in Jiaxing City, Zhejiang province, in the Yangtze River Delta (YRD) region. We first analyzed the air quality changes during four meteorological regimes and then compared the air pollutant concentrations before, during, and after the regulation under static meteorological conditions. Next, we conducted modeling scenarios to quantify the effects caused due to the air pollution control measures. We found that total emissions of SO2, NOx, PM2.5, and volatile organic compounds (VOCs) in Jiaxing were reduced by 56 %, 58 %, 64 %, and 80 %, respectively, while total emission reductions of SO2, NOx, PM2.5, and VOCs over the YRD region are estimated to be 10 %, 9 %, 10 %, and 11 %, respectively. Modeling results suggest that during the campaign from 8 to 18 December, PM2.5 daily average concentrations decreased by 10 µg m−3 with an average decrease of 14.6 %. Our implemented optimization analysis compared with previous studies also reveals that local emission reductions play a key role in air quality improvement, although it shall be supplemented by regional linkage. In terms of regional joint control, implementing pollution channel control 48 h before the event is of most benefit in getting similar results. Therefore, it is recommended that a synergistic emission reduction plan between adjacent areas with local pollution emission reductions as the core part should be established and strengthened, and emission reduction plans for different types of pollution through a stronger regional linkage should be reserved.

Seasonal Changes of Airborne Bacterial Communities Over Tokyo and Influence of Local Meteorology.

In order to study airborne bacterial community dynamics over Tokyo, including fine-scale correlations between airborne microorganisms and meteorological conditions, and the influence of local versus long-range transport of microbes, air samples were collected on filters for periods ranging from 48 to 72 h. The diversity of the microbial community was assessed by next generation sequencing. Predicted source regions of airborne particles, from back trajectory analyses, changed abruptly from the Pacific Ocean to the Eurasian Continent in the beginning of October. However, the microbial community composition and the alpha and beta diversities were not affected by this shift in meteorological regime, suggesting that long-range transport from oceanic or continental sources was not the principal determinant controlling the local airborne microbiome. By contrast, we found a significant correlation between the local meteorology, especially relative humidity and wind speed, and both alpha diversity and beta diversity. Among four potential local source categories (soil, bay seawater, river, and pond), bay seawater and soil were identified as constant and predominant sources. Statistical analyses point toward humidity as the most influential meteorological factor, most likely because it is correlated with soil moisture and hence negatively correlated with the dispersal of particles from the land surface. In this study, we have demonstrated the benefits of fine-scale temporal analyses for understanding the sources and relationships with the meteorology of Tokyo’s “aerobiome.”

Theory for spectral broadening of narrowband signals in the atmosphere and experiment with an acoustic source onboard an unmanned aerial vehicle.

Narrowband acoustic signals propagating through inhomogeneous moving media, such as atmospheric turbulence, exhibit spectral broadening. This phenomenon has been previously studied with regard to acoustic remote sensing of the atmosphere with sodars and tonal noise of turbofan aircraft engines. In this paper, spectral broadening is studied for line-of-sight sound propagation in a turbulent atmosphere. The averaged power spectral density of a narrowband signal is calculated from a Fourier transform of the temporal mutual coherence function of the sound field. Spectral broadening is characterized by the width of the spectral density. The spectral width is calculated for the Kolmogorov spectra of temperature and wind velocity fluctuations for both horizontal and slanted propagation in the atmosphere. In the latter case, the height-dependence of the wind speed and turbulence parameters is addressed. The spectral width is studied numerically for different meteorological regimes of the atmospheric boundary layer characterized by the friction velocity and the surface sensible heat flux. Theoretical results are compared to experimental data for propagation from an acoustic multi-tone source onboard an unmanned aerial vehicle to a microphone array located on the ground.

Tidal and Meteorological Influences on the Growth of Invasive Spartina alterniflora: Evidence from UAV Remote Sensing

Rapid invasion of Spartina alterniflora into Chinese coastal wetlands has attracted much attention. Many field and remote sensing studies have examined the spatio-temporal dynamics of S. alterniflora invasion; however, spatially explicit quantitative analyses of S. alterniflora invasion and its underlying mechanisms at both patch and landscape scales are seldom reported. To fill this knowledge gap, we integrated multi-temporal unmanned aerial vehicle (UAV) imagery, light detection and ranging (LiDAR)-derived elevation data, and tidal and meteorological time series to explore the growth potential (lateral expansion rates and canopy greenness) of S. alterniflora over the intertidal zone in a subtropical coastal wetland (Zhangjiang estuarine wetland, Fujian, China). Our analyses of patch expansion indicated that isolated S. alterniflora patches in this wetland experienced high lateral expansion over the past several years (averaged at 4.28 m/year in patch diameter during 2014–2017), and lateral expansion rates ( y , m/year) showed a statistically significant declining trend with increasing inundation ( x , h/day; 3 ≤ x ≤ 18 ): y = − 0.17 x + 5.91 , R 2 = 0.78 . Our analyses of canopy greenness showed that the seasonality of the growth potential of S. alterniflora was driven by temperature (Pearson correlation coefficient r = 0.76 ) and precipitation ( r = 0.68 ), with the growth potential peaking in early/middle summer with high temperature and adequate precipitation. Together, we concluded that the growth potential of S. alterniflora was co-regulated by tidal and meteorological regimes, in which spatial heterogeneity is controlled by tidal inundation while temporal variation is controlled by both temperature and precipitation. To the best of our knowledge, this is the first spatially explicit quantitative study to examine the influences of tidal and meteorological regimes on both spatial heterogeneity (over the intertidal zone) and temporal variation (intra- and inter-annual) of S. alterniflora at both patch and landscape scales. These findings could serve critical empirical evidence to help answer how coastal salt marshes respond to climate change and assess the vulnerability and resilience of coastal salt marshes to rising sea level. Our UAV-based methodology could be applied to many types of plant community distributions.

Using the terrestrial laser scanning technique for aeolian sediment transport assessment in the coastal zone in seasonal scale

Based on an analysis of a series of digital elevation models obtained using a terrestrial laser scanning (TLS) technique, assessment of mean sand transport rate was performed in seasonal scale. Analytical procedures based on the method of finite differences were performed to quantify the volume of moved material. Coastal hydrodynamic processes, as well as the meteorological regime were taken into account as forcing or limiting factors of aeolian processes. The TLS method is successfully used to assess variability and embryo dunes formation in different areas by other researchers. Two characteristic coastal areas on the territory of the Сuronian Spit National Park in Southeastern Baltic Sea were selected as key sites for morphodynamic processes studying. The results of the analysis of coastal hydrodynamic and related morphodynamic processes show that only one site is suitable for estimating the average rate of sand transport on a seasonal scale. The received relationship between cross-shore mean sand transport rate and the cross-shore directions average wind speed are in a good agreement with the Bagnold formula and with field measurements using sand traps. Extreme hydrodynamic situations leading to beach inundation, as well as precipitation, limit the development of aeolian processes on a seasonal scale.

Temporal variations of the conduction current density during fair weather days in Israel

Ground-based measurements of the atmospheric conduction current density were conducted on Mount Hermon in northern Israel (33°18′N 35°47.2′E, 2050 m a.s.l). The aim was to measure the conduction current diurnal behavior during days that are defined meteorologically as fair weather days. Results from 86 selected fair weather days show an average value of 0.9 pA/m2 downward, and a double oscillation behavior of the conduction current density with two maxima – a morning peak due to local effect and an evening peak due to global effect, with lower values in between. Fourier transform analysis applied to the continuous data shows the two maxima peaks under the daily background level. The conduction current density, together with the fair weather vertical electric field was used to calculate the fair weather mean conductivity behavior (based on Ohm's law). The conductivity shows minimum values during local noon hours when the station is assumed to be within the boundary layer and high conductivity values during the night hours when the station is above the boundary layer. This is likely due to the respective diurnal changes in concentrations of aerosol particles. A WRF simulation of a single fair weather day was conducted in order to determine the meteorological regime and the boundary layer height and is presented to support the hypothesis that conductivity values depend, at least in part, on the height of the boundary layer relative to the station.

Evidence for Changes in Arctic Cloud Phase Due to Long‐Range Pollution Transport

AbstractReduced precipitation rates allow pollution within air parcels from midlatitudes to reach the Arctic without being scavenged. We use satellite and tracer transport model data sets to evaluate the degree of supercooling required for 50% of a chosen ensemble of low‐level clouds to be in the ice phase for a given meteorological regime. Our results suggest that smaller cloud droplet effective radii are related to higher required amounts of supercooling but that, overall, pollution plumes from fossil fuel combustion lower the degree of supercooling that is required for freezing by approximately 4 °C. The relationship between anthropogenic plumes and the freezing transition temperature from liquid to ice remains to be explained.

Foredune morphodynamics and sediment budgets at seasonal to decadal scales: Humboldt Bay National Wildlife Refuge, California, USA

Coastal foredunes are shore-parallel ridges that form in the backshore and their morphodynamics are controlled partly by seasonal and spatial variations in the coastal (onshore) sediment budget that, in turn, are driven by oceanic and atmospheric processes and interactions, including regional wave and wind regimes, climatic variability events (e.g., ENSO), sediment availability, beach characteristics (e.g., width, slope), and vegetation type and cover in the backshore. Previous studies on shoreline change in Northern California report only broad rates of erosion and accretion related to regional meteorological regimes. This study presents a more detailed, multi-decadal to seasonal account of shoreline response and foredune morphodynamics along a 2.5 km stretch of coast in the Humboldt Bay National Wildlife Refuge (HBNWR). Analysis of historical aerial photography (1939–2014) reveals trends in shoreline position that are coupled with more detailed assessments of foredune morphodynamics and seasonal scale volumetric changes from cross-shore topographic profiles``. These findings set the historical context of foredune morphodynamics and allow exploration of the implications of seasonal meteorological variation on long-term (75-year) foredune evolution and development at the HBNWR.DSAS describes maximum foredune progradation in the north (up to +0.51 m a−1) and maximum foredune retreat in the south (up to −0.49 m a−1). Aerial photograph analysis (2004–2014) shows statistically significant larger erosive features in the southern zone than in the northern and central zones. Seasonal volume calculations from cross-shore profiles indicate statistically significant differences in alongshore transect elevation and foredune volume, with larger elevations and volumes in the northern and central zones than in the southern. Combined with evidence of seasonal bidirectional littoral drift, these data support a north to south gradient in sediment availability, foredune position and resulting stages of established foredune development. Seasonal storm energies and climate forcing events introduce variability in erosive patterns but support the persistence of alongshore developmental stages. Future research should explore foredune morphodynamics on a smaller spatial scale and changes related to the presence/absence of multiple vegetation assemblages.

“Dendrology” in Numerical Weather Prediction: What Random Forests and Logistic Regression Tell Us about Forecasting Extreme Precipitation

Three different statistical algorithms are applied to forecast locally extreme precipitation across the contiguous United States (CONUS) as quantified by 1- and 10-yr average recurrence interval (ARI) exceedances for 1200–1200 UTC forecasts spanning forecast hours 36–60 and 60–84, denoted, respectively, day 2 and day 3. Predictors come from nearly 11 years of reforecasts from NOAA’s Second-Generation Global Ensemble Forecast System Reforecast (GEFS/R) model and derive from a variety of thermodynamic and kinematic variables that characterize the meteorological regime in addition to the quantitative precipitation forecast (QPF) output from the ensemble. In addition to encompassing nine different atmospheric fields, predictors also vary in space and time relative to the forecast point. Distinct models are trained for eight different hydrometeorologically cohesive regions of the CONUS. One algorithm supplies the GEFS/R predictors directly to a random forest (RF) procedure to produce extreme precipitation forecasts; the second also employs RFs, but the predictors instead undergo principal component analysis (PCA), and extracted leading components are supplied to the RF. In the last algorithm, dimension-reduced predictors are supplied to a logistic regression (LR) algorithm instead of an RF. A companion paper investigated the quality of the forecasts produced by these models and other RF-based forecast models. This study is an extension of that work and explores the internals of these trained models and what physical and statistical insights they reveal about forecasting extreme precipitation from a global, convection-parameterized model.

Money Doesn't Grow on Trees, but Forecasts Do: Forecasting Extreme Precipitation with Random Forests

Abstract Approximately 11 years of reforecasts from NOAA’s Second-Generation Global Ensemble Forecast System Reforecast (GEFS/R) model are used to train a contiguous United States (CONUS)-wide gridded probabilistic prediction system for locally extreme precipitation. This system is developed primarily using the random forest (RF) algorithm. Locally extreme precipitation is quantified for 24-h precipitation accumulations in the framework of average recurrence intervals (ARIs), with two severity levels: 1- and 10-yr ARI exceedances. Forecasts are made from 0000 UTC forecast initializations for two 1200–1200 UTC periods: days 2 and 3, comprising, respectively, forecast hours 36–60 and 60–84. Separate models are trained for each of eight forecast regions and for each forecast lead time. GEFS/R predictors vary in space and time relative to the forecast point and include not only the quantitative precipitation forecast (QPF) output from the model, but also variables that characterize the meteorological regime, including winds, moisture, and instability. Numerous sensitivity experiments are performed to determine the effects of the inclusion or exclusion of different aspects of forecast information in the model predictors, the choice of statistical algorithm, and the effect of performing dimensionality reduction via principal component analysis as a preprocessing step. Overall, it is found that the machine learning (ML)-based forecasts add significant skill over exceedance forecasts produced from both the raw GEFS/R ensemble QPFs and from the European Centre for Medium-Range Weather Forecasts’ (ECMWF) global ensemble across almost all regions of the CONUS. ML-based forecasts are found to be underconfident, while raw ensemble forecasts are highly overconfident.

Simulating global horizontal irradiance in the Arabian Peninsula: Sensitivity to explicit treatment of aerosols

Global horizontal irradiance (GHI) is simulated using a three-dimensional atmospheric meteorology-chemistry model and a triple-nesting configuration over the Middle East with a focus on the hot desert climate of Qatar. The model performance was assessed with measurement data of solar radiation from a ground monitoring station in Doha (Qatar) collected over a three-month period, of representative and distinct meteorological regimes. We have examined the ability of the model to reproduce GHI values under two different shortwave downward radiation parameterizations, and assessed the sensitivity of our results to the presence of aerosols. The introduction of an advanced treatment of aerosols greatly improves the model performance in predicting GHI. Explicitly including aerosol processes and its emissions in the model significantly reduces the relative root mean square error for GHI from 25% to 13% in May and from 20% to 12% in August. A significant improvement of the systematic bias was achieved (from up to 30% to approximately 2%) when aerosols are fully considered during all three seasons. The RRTM (Rapid Radiative Transfer Model) shortwave radiation scheme performs somewhat better than the Goddard scheme both with and without aerosols. This work suggests that GHI predictions in regions that experience high aerosol loadings can benefit significantly from a detailed and explicit treatment of aerosols and their physicochemical processes. This offers a novel approach to better manage the fluctuating nature of solar radiation originating from variable weather and air pollution conditions.

An analysis of air quality status over an industrial city from past years and its impact on health aspects

Due to rapid industrialisation and urbanisation, Kochi (9°58' N, 76°17' E) needs due considerations in pollution point of view. The pollution level in terms of concentration of SO2, NOx and suspended particular matter (SPM) shows high values with frequent abnormal values. To study the total effect of all these pollutants, Oak Ridge Air Quality Index (ORAQI) was calculated using monthly mean data. The results showed considerable deterioration in air quality over the years with the index showing one to three levels of deterioration over different zones. Analysis of meteorological regimes over the area pointed out that the city is highly susceptible to high pollution load. Wind, mixing height and ventilation coefficient showed lower values throughout the year, which shows meteorological conditions are not favourable for dispersion of pollutants over this coastal station. The gravimetric estimates of PM10, sampled from different locations in Kochi, showed concentrations above the air quality standard. Chemical analysis of these aerosol samples for anionic and cationic species was done using ion chromatography, atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Estimates of water soluble component, mineral dust and organic carbon contribute to 26-48% of aerosol mass. Statistical analysis of chemical composition data revealed anthropogenic components to be the dominant factor, with mineral dust being the second factor. At all the experimental locations, SO4 2- was the most dominant species, indicating the strong anthropogenic influence. As a preliminary study on health impact, we focused on the ARI Acute Respiratory Illness (ARI) cases in children. There are certain pockets which showed more incidence of ARI, which is evidently related to pollution problems. Anthropogenic activities linked with the orientation of the coast and sea breeze have link with the ARI cases surrounding the area. Note: This work was partially presented at 5th Edition of EuroSciCon Conference on Environmental Science and Engineering Expert scheduled during October 29-30, 2018 Budapest, Hungary

Mesoscale modelling of the summer climate response of Moscow metropolitan area to urban expansion

In this paper, the experience of applying a regional climate model to simulating the summer climate features of Moscow metropolitan area is examined. Also, an assessment is made of climate response to the implementation of a scenario of twofold city expansion. The model (COSMO-CLM) was adapted to the conditions of the region under investigation, supplemented by specific urban canopy parameterization and equipped with realistic parameters of urban surface. It was possible to successfully simulate the summer meteorological regime of Moscow region and, specifically, the temporal and spatial variability of the Moscow urban heat island (UHI). First results of the simulation for the city expansion show that the new urbanized areas on the periphery of Moscow have a heating impact on its central part, which leads to an increase of the UHI effect, on the average, of 10% (in the central area). In extreme heat events the temperature response to this scenario is much stronger, which may deteriorate human health and increase thermal stress. The simulation results also show that the city of Moscow is characterized by a positive anomaly of summer precipitation (in the city and its leeward side it increases by 10-30%). The scenario of urban expansion enhances this anomaly by 5-10% and increases its area.

Uncertainty from the choice of microphysics scheme in convection-permitting models significantly exceeds aerosol effects

Abstract. This study investigates the hydrometeor development and response to cloud droplet number concentration (CDNC) perturbations in convection-permitting model configurations. We present results from a real-data simulation of deep convection in the Congo basin, an idealised supercell case, and a warm-rain large-eddy simulation (LES). In each case we compare two frequently used double-moment bulk microphysics schemes and investigate the response to CDNC perturbations. We find that the variability among the two schemes, including the response to aerosol, differs widely between these cases. In all cases, differences in the simulated cloud morphology and precipitation are found to be significantly greater between the microphysics schemes than due to CDNC perturbations within each scheme. Further, we show that the response of the hydrometeors to CDNC perturbations differs strongly not only between microphysics schemes, but the inter-scheme variability also differs between cases of convection. Sensitivity tests show that the representation of autoconversion is the dominant factor that drives differences in rain production between the microphysics schemes in the idealised precipitating shallow cumulus case and in a subregion of the Congo basin simulations dominated by liquid-phase processes. In this region, rain mass is also shown to be relatively insensitive to the radiative effects of an overlying layer of ice-phase cloud. The conversion of cloud ice to snow is the process responsible for differences in cold cloud bias between the schemes in the Congo. In the idealised supercell case, thermodynamic impacts on the storm system using different microphysics parameterisations can equal those due to aerosol effects. These results highlight the large uncertainty in cloud and precipitation responses to aerosol in convection-permitting simulations and have important implications not only for process studies of aerosol–convection interaction, but also for global modelling studies of aerosol indirect effects. These results indicate the continuing need for tighter observational constraints of cloud processes and response to aerosol in a range of meteorological regimes.

Appraisal of Drought Characteristics of Representative Drought Indices using Meteorological Variables

In order to efficiently utilize meteorological drought indices, meteorological variables were compared with drought characteristics from the widely known Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). The results of this study indicate that SPI overestimated drought severity and SPEI overestimated drought frequency and length under the same weather conditions. For droughts of high severity and short duration, the shortage of precipitation was the dominant cause for the occurrence of drought. For investigation on drought duration, it was revealed that precipitation was the dominant variable influencing droughts at short durations. The effect of precipitation on drought decreased at long durations, with the effect of Potential Evapotranspiration (PET) on drought became important. For investigation on drought severity, it was revealed that drought severity was proportional to precipitation in both SPI and SPEI, but other meteorological variables did not have a significant relationship with drought severity. These results mean that the magnitudes of the two drought indices changes in different meteorological regimes and it is possible to contribute to the quantitative decision and the combination of drought indices for meteorological drought.