Air Mass Types Research Articles

Wind Speed Profile Statistics from Acoustic Soundings at a Black Sea Coastal Site

More than seven years of remote sensing data with high spatial and temporal resolution were investigated in this study. The 20-min moving averaged wind profiles form the acoustic sounding with Scintec MFAS sodar were derived every 10 min. The profiles covered from 30 to 600 m height with vertical resolution of 10 m. The wind speed probability and the Weibull distribution parameters were calculated by the maximum likelihood method at each level and then the profiles of the Weibull scale and shape parameters were analyzed. Diurnal wind speed at heights above 200 m has shown a well-expressed increase in the averaged values during the night hours, while during the day lower wind speeds were observed. The reversal height was explored from spatially and temporally homogenized diurnal wind speed data with applied quadratic functions for better interpretation of the results. In addition, analyses by type of air masses (land or sea air mass) were performed. One of the outcomes of the study was assessment of the internal boundary layer height, which was estimated to 50–80 m at the location of the sodar. The obtained information forms the basis for climatological insights on the vertical structure of the coastal boundary layer and is unique long-term data set important not only for Bulgaria but for coastal meteorology in general.

The impact of aerosol size-dependent hygroscopicity and mixing state on the cloud condensation nuclei potential over the north-east Atlantic

Abstract. We present an aerosol cloud condensation nuclei (CCN) closure study over the north-east Atlantic Ocean using six approximating methods. The CCN number concentrations (NCCN) were measured at four discrete supersaturations (SSs; 0.25 %, 0.5 %, 0.75 % and 1.0 %). Concurrently, aerosol number size distribution, sub-saturation hygroscopic growth factor and bulk PM1 chemical composition were obtained at matching time resolution and after a careful data validation exercise. Method A used a constant bulk hygroscopicity parameter κ of 0.3; method B used bulk PM1 chemical composition measured by an aerosol mass spectrometer (AMS); method C utilised a single growth factor (GF) size (165 nm) measured by a humidified tandem differential mobility analyser (HTDMA); method D utilised size-dependent GFs measured at 35, 50, 75, 110 and 165 nm; method E divided the aerosol population into three hygroscopicity modes (near-hydrophobic, more-hygroscopic and sea-salt modes), and the total CCN number in each mode was cumulatively added up; method F used the full-size-scale GF probability density function (GF–PDF) in the most complex approach. The studied periods included high-biological-activity and low-biological-activity seasons in clean marine and polluted continental air masses to represent and discuss the most contrasting aerosol populations. Overall, a good agreement was found between estimated and measured NCCN with linear regression slopes ranging from 0.64 to 1.6. The temporal variability was captured very well, with Pearson's R value ranging from 0.76 to 0.98 depending on the method and air mass type. We further compared the results of using different methods to quantify the impact of size-dependent hygroscopicity and mixing state and found that ignoring size-dependent hygroscopicity induced overestimation of NCCN by up to 12 %, and ignoring a mixing state induced overestimation of NCCN by up to 15 %. The error induced by assuming an internal mixing in highly polluted cases was largely eliminated by dividing the full GF–PDF into three conventional hygroscopic modes, while assuming an internal mixing in clean marine aerosol did not induce significant error.

Influence of Atmospheric Circulation on Cloudiness and Cloud Types in Petuniabukta and Svalbard-Lufthavn in Summer 2016

The paper analyzes the influence of atmospheric circulation on cloudiness and cloud types during July and August of 2016 in Petuniabukta and Svalbard-Lufthavn. For the meteorological parameters, basic statistical measures were calculated and the average diurnal cloud patterns were analyzed. Taking the data from meteorological reanalysis (NCEP/NCAR-The National Centers for Atmospheric Prediction/The National Center for Atmospheric Research) regarding the mean sea-level pressure (SLP), 500 hPa geopotential height, and air temperature at 850 hPa (T850), composite maps of the synoptic situation for the studied area were constructed. For the observed types of clouds, the frequency of their occurrence in particular types of atmospheric circulation was then determined according to the Niedźwiedź classification. Differences in the amount of cloudiness in the examined measuring points were ascertained. The occurrence of cloud types is associated with both the direction of air mass advection and type of circulation. The results may also indicate the possibility of influence from specific, local environmental features on cloudiness.

The effects of continentality, marine nature and the recirculation of air masses on pollen concentration: Olea in a Mediterranean coastal enclave

Olea pollen concentrations have been studied in relation to the typology of air masses, pollen grain sources and marine nature during advections in a coastal enclave in the south-eastern Iberian Peninsula. Since Spain is the world's leading olive producer, and olive growing extends throughout the Mediterranean basin, this location is ideal for the study of long-distance transport events (LTD) during the main pollen season (MPS). The air masses were classified using the calculation of 48-h back trajectories at 250, 500 and 750 m above ground level using the HYSPLIT model. After that, the frequency of LDT events from Africa and Europe was found to be 8.7% of the MPS days. In contrast, regional air masses were found in 38.6% of the MPS days. This was reflected in pollen concentrations, with significantly higher concentrations (p-value <0.05) on days with regional air masses compared to days with European air masses. Regarding the source areas, the importance of nearby sources with intense olive cultivation was confirmed (i.e., Andalusia). This proximity was relevant beyond the attenuations observed when the advections acquired a marine nature as the air mass back trajectories moved over the sea (p-value <0.001). The review of air mass typologies, source areas and pollen concentrations resulted in establishing peak dates and the detection of LDT associated with these peak dates. Distortions in the typical path of each air mass explained alterations in pollen concentrations on consecutive days. The recirculation and loops of the air mass back trajectories varied the pollen load that every type of air mass could originally contain.

An ANN Model Trained on Regional Data in the Prediction of Particular Weather Conditions

Artificial Neural Networks (ANNs) have proven to be a powerful tool for solving a wide variety of real-life problems. The possibility of using them for forecasting phenomena occurring in nature, especially weather indicators, has been widely discussed. However, the various areas of the world differ in terms of their difficulty and ability in preparing accurate weather forecasts. Poland lies in a zone with a moderate transition climate, which is characterized by seasonality and the inflow of many types of air masses from different directions, which, combined with the compound terrain, causes climate variability and makes it difficult to accurately predict the weather. For this reason, it is necessary to adapt the model to the prediction of weather conditions and verify its effectiveness on real data. The principal aim of this study is to present the use of a regressive model based on a unidirectional multilayer neural network, also called a Multilayer Perceptron (MLP), to predict selected weather indicators for the city of Szczecin in Poland. The forecast of the model we implemented was effective in determining the daily parameters at 96% compliance with the actual measurements for the prediction of the minimum and maximum temperature for the next day and 83.27% for the prediction of atmospheric pressure.

Source Apportionment of Ozone Pollution in Guangzhou: Case Study with the Application of Lagrangian Photochemical Trajectory Model

A six-day ozone pollution episode in Guangzhou in early October 2018 was analyzed with the application of a Lagrangian photochemical trajectory model to trace the sources of ozone, quantify the contributions of different regions, and evaluate the effects of emission reduction measures targeted at different emission sectors and different precursors on ozone pollution. The results showed that during the ozone pollution episode, the maximum daily 8 h ozone exceeded 160 μg·m-3 and the highest value reached 271 μg·m-3. The average concentrations of nitrogen oxides and volatile organic compounds (VOCs) were (77.7±42.8) μg·m-3 and (71.9±56.2) μg·m-3, respectively. Aromatics and alkenes were the dominant reactive VOCs, with contributions of 38% and 30% to·OH reactivity and 51% and 16% to ozone formation potential, respectively. The ozone pollution in Guangzhou during this episode was affected by three types of air masses, with the primary source regions of Guangzhou, Guangdong Province, and regions outside Guangdong Province. For all three air mass types, ozone production in these source region was controlled by VOCs. Sensitivity tests showed that, in the primary source regions, reducing the emissions of VOCs is more effective than reducing NOx in terms of reducing ozone concentrations. Under the condition of full emission reduction, regulating traffic emissions could substantially reduce ozone levels by 14.6%-21.0% in Guangzhou, which was a more significant reduction than regulating controlled industry (8.4%-15.3%), power plant (0.9%-6.2%) and residential (2.3%-4.7%) emissions. However, the traffic emission reduction is not as effective (induced ozone reduction<10%) when the emissions reduction ratio is lower than 90%. In addition, biogenic emissions in the Pearl River Delta also substantially contributed to the ozone levels under certain circumstances, as indicated by the ozone reduction up to 19% when biogenic emissions were shut off.

Impact of various air mass types on cloud condensation nuclei concentrations along coastal southeast Florida

Coastal southeast Florida experiences a wide range of aerosol conditions, including African dust, biomass burning (BB) aerosols, as well as sea salt and other locally-emitted aerosols. These aerosols are important sources of cloud condensation nuclei (CCN), which play an essential role in governing cloud radiative properties. As marine environments dominate the surface of Earth, CCN characteristics in coastal southeast Florida have broad implications for other regions with the added feature that this site is perturbed by both natural and anthropogenic emissions. This study investigates the influence of different air mass types on CCN concentrations at 0.2% (CCN0.2%) and 1.0% (CCN1.0%) supersaturation (SS) based on ground site measurements during selected months in 2013, 2017, and 2018. Average CCN0.2% and CCN1.0% concentrations were 373 ± 200 cm−3 and 584 ± 323 cm−3, respectively, for four selected days with minimal presence of African dust and BB (i.e., background days). CCN concentrations were not elevated on the four days with highest influence of African dust (289 ± 104 cm−3 [0.2% SS] and 591 ± 302 cm−3 [1.0% SS]), consistent with high dust mass concentrations comprised of coarse particles that are few in number. In contrast, CCN concentrations were substantially enhanced on the five days with the greatest impact from BB (1408 ± 976 cm−3 [0.2% SS] and 3337 ± 1252 cm−3 [1.0% SS]). Ratios of CCN0.2%:CCN1.0% were used to compare the hygroscopicity of the aerosols associated with African dust, BB, and background days. Average ratios were similar for days impacted by African dust and BB (0.54 ± 0.17 and 0.55 ± 0.17, respectively). A 29% higher average ratio was observed on background days (0.71 ± 0.14), owing in part to a strong presence of sea salt and reduced presence of more hydrophobic species such as those of a carbonaceous or mineral-dust nature. Finally, periods of heavy rainfall were shown to effectively decrease both CCN0.2% and CCN1.0% concentrations. However, the rate varied at which such concentrations increased after the rain. This work contributes knowledge on the nucleating ability of African dust and BB in a marine environment after varying periods of atmospheric transport (days to weeks). The results can be used to understand the hygroscopicity of these air mass types, predict how they may influence cloud properties, and provide a valuable model constraint when predicting CCN concentrations in comparable situations.

Altitude Aerosol Measurements in Central France: Seasonality, Sources and Free‐Troposphere/Boundary Layer Segregation

AbstractThe chemical composition of nonrefractory submicron aerosol particles was measured at the Puy‐de‐Dôme (PUY) station (1,465 m a.s.l) during 2015 using a Time‐of‐Flight Aerosol Chemical Speciation Monitor (ToF‐ACSM). These aerosol chemistry measurements are combined with online black carbon (BC) measurements to provide an overview of the submicron aerosol composition. Averaged over the entire year, and normalized to standard temperature and pressure, organic aerosol (OA) dominates the PM1 concentration during all seasons and within all air mass types (2.12 ± 1.73 µgm−3), and is responsible for summertime increases in aerosol concentration. Highest mass concentrations were measured during the summer, when air masses were arriving over mainland Europe and lowest in the winter months (when most air masses were of Atlantic origin). OA source apportionment was performed separately during each season, using the Source Finder (SoFi) interface for the multilinear engine. The PUY site, situated at 1,465 m a.s.l, although mainly sampling in the atmospheric boundary layer, it is sometimes sampling in the lower free troposphere (FT), providing the opportunity to identify the characteristics of FT aerosol. In order to accurately identify these sampling periods, the methodology described in Farah et al. (2018), during the same time period (2015/2016), was applied to the data. During this period, FT air masses are sampled approximately 20% of the time. This work provides, on one hand, a description of long‐term aerosol chemical properties at a remote regional site in central Europe and, on the other hand a characteristic chemical signature of FT aerosols over this region. This data can be used to improve our understanding of the transport and aging properties of aerosols at regional observation sites.

Spatial diversity of air temperature changes in Poland in 1961–2018

The article comprises an analysis of the spatial distribution, and variability of air temperature in Poland in the years 1961–2018. It was found that the mean increase in air temperature was 0.33 °C/10 years. The most evident warming occurred in the west of the country and at the Baltic Sea (> 0.4 °C/10 years). The greatest increase in the temperature was observed in summer (July 0.48 °C/10 years), winter (January 0.46 °C/10 years) and spring (April 0.41 °C/10 years), whereas in autumn the warming was not statistically significant. The major role of atmospheric circulation in shaping air temperature in Poland was corroborated. The positive correlation with the NAO was confirmed, and Pearson’s linear correlation coefficient (r) reached 0.81 in the north of Poland in January. An analysis of the variability of air temperature in Torun (Central Poland) in 1991–2018 demonstrated that the increase in temperature was correlated with a solar irradiance (r = 0.69 in July). Moreover, the types of atmospheric circulation and incoming air masses are also significant. The type of baric centre was found to play a very important role that is opposite in winter to what it is in summer. In cyclonic situations, air temperature increased in winter (r = 0.65 in January) and decreased in the warm half of the year (r = − 0.47 in September). An intensified flow of incoming air masses from the west caused air temperature to increase in winter (r = 0.72 in January) and to cool in summer (r = − 0.69 in August). The role of meridional flow becomes particularly evident in autumn (r = 0.49 in October).

Factors Influencing New Atmospheric Particle Formation in Ordos During Summer and Autumn 2019

In this study, the aerosol number size distribution in the range of 10 nm-10 μm was collected from August 16 to October 04, 2019 at Ordos using a wide-range particle spectrometer (WPS). Combined with PM (PM2.5 and PM10), pollution gases, meteorological data, and the HYSPLIT model, the characteristics and impact factors of new particle formation (NPF) were discussed. The results indicated that there were 19 NPF events during the observation period, which have different effects on diurnal variation in aerosol number concentration in different modes. The NPF events caused a sharp increase in the number concentration of nucleation and Aitken mode aerosols, but had little effect on the number concentration of accumulation and coarse mode aerosols. The temperature, wind speed, and total solar radiation during NPF days were usually higher than those in non-NPF days, and the RH during NPF days was lower. On NPF days, the mass concentrations of PM2.5, PM10, CO, and NO2 were lower than those on non-NPF days, while the mass concentrations of O3 and SO2 were higher. NPF events were observed in 40.0% of northern air masses and 29.6% of southern air masses. There were significant differences in meteorological elements in different NPF event air mass types. The southern NPF event air mass type had the lowest wind speed and the highest RH, with averages of (2.4±1.5) m·s-1 and (48.8±10.8)%, respectively. The northern NPF event air mass type had the highest wind speed and total solar radiation, with averages of (4.2±1.9) m·s-1 and (664.5±255.6) W·m-2, respectively. The western air mass type of NPF event had the lowest RH, with an average of (29.8±12.7)%. The formation rates of new particles in the different air mass types of NPF events were similar, ranging from 1.5 to 1.8 cm-3·s-1. The largest growth rate was (12.7±13.6) nm·h-1 in the southern NPF event air mass type, which was 1.2 times and 1.4 times higher than the NPF events of northern air masses and western air masses.

Daily and seasonal variabilities of thermal stress (based on the UTCI) in air masses typical for Central Europe: an example from Warsaw

The objective of research involved the comparison of daily and seasonal courses of thermal stress occurring in Central Europe depending on the inflowing air mass. The analysis used data from Warsaw (1991–2000), including air temperature (°C), water vapour pressure (hPa), wind speed (m s−1) and cloud cover (%). Universal thermal climate index was calculated and subsequently averaged for the individual months and four types of atmospheric air masses: polar maritime (mP), arctic(A), polar continental (cP) and tropical (T). The studies analysed differences in daily patterns of the averaged values of universal thermal climate index between air masses and determined the frequency of days with various types of thermal stress in individual air masses. The analyses indicated that under the conditions of Central Europe, the highest daily variance of biothermal conditions occurs between the masses of cP and T in the spring and autumn. Considerably greater diversity of biothermal conditions was observed between the masses during daytime compared with nighttime, especially in the warm half of the year. The thermal stress, which can be encountered in Central Europe, ranges from an “extreme cold stress” in winter at night and early morning hours to “very strong heat stress” in summer at noon. Extreme thermal stress is related primarily to the masses of cP, A and T. The most optimal biothermal conditions occur during the advection of mP air.

Growing Season Air mass Equivalent Temperature (TE) in the East Central USA

Equivalent temperature (TE), which incorporates both dry (surface air temperature, T) and moist heat content associated with atmospheric moisture, is a better indicator of overall atmospheric heat content compared to T alone. This paper investigates the impacts of different types of air masses on TE during the growing season (April–September). The study used data from the Kentucky Mesonet for this purpose. The growing season was divided into early (April–May), mid (June–July), and late (August–September). Analysis suggests that TE for moist tropical (MT) air mass was as high as 61 and 81 °C for the early and mid-growing season, respectively. Further analysis suggests that TE for different parts of the growing seasons were statistically significantly different from each other. In addition, TE for different air masses was also statistically significantly different from each other. The difference between TE and T (i.e. TE-T) is smaller under dry atmospheric conditions but larger under moist conditions. For example, in Barren County, the lowest difference (20–10 °C) was 10 °C. It was reported on 18 April 2010, a dry weather day. On the other hand, the highest difference for this site was 48 °C and was reported on 11 August 2010, a humid day.

Modeling the Aerosol Extinction in Marine and Coastal Areas

Sea salt aerosol (SSA) significantly affects the atmospheric albedo, the radiation balance of the Earth, and has consequences for global and regional climate. There is currently no reliable radiative large-scale aerosol model of the marine and coastal atmosphere. All these lead to uncertainties in radiation boxes, short-term weather forecasts, and climate models and to uncertainties in interpretation of the lidar return data obtained and at the development of new lidar systems. The MaexPro model is shown to calculate adequately the aerosol extinction coefficients $\varepsilon (\lambda)$ and the concentration of SSA particles for different wind regimes, fetches, and humidity. The calculated $\varepsilon (\lambda)$ profiles well agree with the experimental data and with calculations using Advanced Navy Aerosol Model (ANAM) and MODTRAN codes. A new approach in studying the influence of the meteorological parameters on spectral $\varepsilon (\lambda)$ gives a new explanation for previously obtained conflicting experimental data, namely, to the effect of decreasing transparency, manifested in the coastal zone, and makes it possible indirectly to account for the type of air mass (marine or coastal). It is shown that the particle size distribution functions and spectral $\varepsilon (\lambda)$ , calculated using the model with the input parameters corresponding most closely to the conditions of experiment, agree well with observations, using OLAF transmissometer, and calculations using MODTRAN code and the experimental results receiving the same conditions of observations (numerical or field). The results obtained are of interest both in the calculations of radiative characteristics of the atmosphere and in interpretation of the lidar return data and calibration signal when developing new lidar systems.

Characterization of Aerosol Physical and Optical Properties at the Observatoire Pérenne de l’Environnement (OPE) Site

The Observatoire Pérenne de l’Environnement (OPE) station is a rural background site located in North-Eastern France. Besides emissions from agricultural activities, the site is located far from local emissions but at an even distance from the intense emission zones of Western Germany to the north-east and the Paris area to the south-west. In the paper, we report and analyze almost six years of measurements (1 May 2012 to 31 December 2018) of the optical and physical properties of aerosol particles. Based on aerosol optical and physical measurements combined with air mass back-trajectories, we investigate the dependence of these properties on air mass type. Two distinct equivalent black carbon (EBC) sources—origins-fossil fuel (FF) and biomass burning (BB)— were identified. FF was the dominant source of EBC (&gt;70%) but showed a very marked seasonal variation. BB fraction is found higher during the cold seasons in the order of 35% (0.1 µg m−3) against 17% (0.05 µg m−3) during the warm seasons. The highest EBC and N0.54–1.15 (particles whose diameter ranged from 0.54 to 1.15 µm) median concentrations were observed during the night time and during the cold seasons compared to the warmer seasons, indicating primary sources trapped within a thin boundary layer (BL). A different behavior is found for N10–550 (particles whose diameter ranged from 10 to 550 nm) and coarse mode particles (N1.15–4.5, i.e., particles whose diameter ranged from 1.15 to 4.5 µm) median concentrations, which were observed during the warm seasons compared to the cold seasons, indicating rather biogenic secondary sources for the smaller particles, and potentially primary biogenic sources for the coarse mode particles. The scattering and absorption coefficients and single scattering albedo (SSA) show the same seasonal variations like the ones of N0.54–1.15 concentrations, indicating that particles larger than 500 nm seemed to contribute the most to the optical properties of the aerosol.

ДИНАМІКА ТА БАГАТОВИМІРНІСТЬ ЛАНДШАФТНО-ТЕХНІЧНИХ СИСТЕМ

The article analyzes the problem of dynamics and multidimensionality of landscapes on the example of landscape and technical systems. The object of the study is a landscape and technical systems, which are characterized by significant dynamics and multidimensionality of the structure. The basis for the publication of the article was the materials of long-term field observations conducted in the framework of research of the Vinnytsia school of anthropogenic landscape science under the direction of H. I. Denysyk. The authors’ contribution is to analyze the dynamics and multidimensionality of the structure and development of the valley-river landscape and technical systems of the Right Bank Ukraine, which lasted during 2007-2019. Knowledge of the dynamics of landscape and technical systems allows one to better understand the specifics of the transformation of the modern landscape sphere and to calculate possible negative trends. It is noted that the dynamics of landscape and technical systems are functional, spatial, and structural transformations, which are manifested in all components to the critical moment of transformation of a block system into a geocomponent one. Four types of dynamics are considered. Chronological dynamics characterize the spatial changes in the boundaries of the landscape and technical system. Structural dynamics involves a change in the morphological structure of the landscape and technical system and the relationships between its blocks. Temporal dynamics unites all changes in the landscape and technical system related to time. Directed dynamics presupposes stable, unilaterally directed transformations of the landscape and technical system with multiple changes of its state and structure. It is noted that each system has its own distinctive feature – multidimensionality, that is, the functioning within it of a number of separate and simultaneously interconnected paradynamic systems. The internal block system is limited by the landscape technosphere of the planet, which combines modern soils, man-made cover, and the air layer. The internal structural-morphological system considers the landscape and the technical system as a clearly defined gradation of taxa. The internal inter-block system provides interconnection in the landscape and technical system at the level of three blocks (managerial, natural and technical). The external complex system expresses the interaction of the landscape and technical system with other landscape complexes. Through the external air system, there is an entry into the landscape and technical system and the reverse radiation of solar radiation and interaction with remote landscape complexes due to the transfer of different types of air masses. In the underlying lithogenic system, the interaction of the landscape and technical system with the lithogenic base, which is represented by the earth’s crust and the upper mantle, is manifested. It is determined that the knowledge of the problems of dynamics and multidimensionality of landscape and technical systems becomes the central problem of engineering landscape science. The development of theoretical aspects of the functioning of landscape and technical systems is of great practical importance. Understanding the specifics of the structure and development of a particular landscape-technical system will increase its economic efficiency and minimize the negative impact on adjacent landscapes. Therefore, in the future, it is necessary to emphasize the research of modern geographers on the problems of multidimensionality and dynamics of different classes of anthropogenic landscapes.

Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

Abstract. This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz–El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm−1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz–El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.

Comparing daily temperature averaging methods: the role of synoptic climatology in determining spatial and seasonal variability

ABSTRACTThe two primary methods for averaging daily near-surface air temperature are twice-daily averaging (i.e., the sum of the maximum and minimum divided by two) and hourly averaging (i.e., using the 24 hourly values of a day). To quantify the influence of synoptic (air mass) climatology on the numerical difference between the two types of daily temperature averaging, a synoptic climatology for 215 weather stations across the Contiguous United States (CONUS) was developed for the period 1981–2010 and then correlated with those difference values. A significant correlation is found between air mass frequency and the temperature difference, especially during the non-transition seasons (i.e., summer and winter). This pattern is due to the influence of air mass type on the shape of the daily temperature curve. The correlation results also show spatial variability, as air masses that are more frequent in the northern CONUS (e.g., Dry Polar) influence the diurnal temperature curve differently than air masses more common in the southern CONUS (e.g., Moist Tropical). Future work can capitalize on these results by investigating different geographic regions and utilizing this correlation-based approach to analyze how anticipated future changes in the synoptic climatology of air masses influence the diurnal temperature curve.

Retrieving Atmospheric and Land Surface Parameters From At-Sensor Thermal Infrared Hyperspectral Data With Artificial Neural Network

The radiances observed by satellites are influenced by both land surface and atmospheric parameters, and it is difficult to retrieve these parameters simultaneously from multispectral measurements with high accuracies. Even though several methods have been proposed, they focus on the retrieval of land surface or atmospheric parameters separately. Generally, these atmospheric parameters are atmospheric water vapor and temperature profiles. Thus, this study aims to establish a back propagation (BP) artificial neural network (ANN) to retrieve land surface emissivity (LSE), land surface temperature (LST), atmospheric transmittance, upward radiance, and downward radiance simultaneously from the hyperspectral thermal infrared (TIR) data, suitable for various air mass types and surface conditions. The principle component analysis technique is first used to compress and remove noise from the data. The evaluation of the ANN using the simulated data without noise indicated that the root mean square error (RMSE) of LST is approximately 0.643 K; the RMSEs of emissivity, transmittance, upward, and downward radiance are approximately 0.0046, 0.005, 0.72, and 2.95 K, respectively. When applied on the simulated data containing noise, the errors of LST, LSE, transmittance, upward, and downward radiance are 1.26, 0.01, 0.01, 1.54, and 4.57 K, respectively. When applied on the real atmospheric infrared sounder data, the retrieved accuracies become worse because of various unstudied reasons. However, the results show that the proposed ANN is promising in retrieving the land surface and atmospheric parameters simultaneously. Because of its simplicity, the proposed ANN can be used to produce preliminary results employed as the first estimates for physics-based retrieval methods.

Merits of novel high-resolution estimates and existing long-term estimates of humidity and incident radiation in a complex domain

Abstract. To provide better and more robust estimates of evaporation and snowmelt in a changing climate, hydrological and ecological modeling practices are shifting towards solving the surface energy balance. In addition to precipitation and near-surface temperature (T2), which often are available at high resolution from national providers, high-quality estimates of 2 m humidity and surface incident shortwave (SW↓) and longwave (LW↓) radiation are also required. Novel, gridded estimates of humidity and incident radiation are constructed using a methodology similar to that used in the development of the WATCH forcing data; however, national 1 km×1 km gridded, observation-based T2 data are consulted in the downscaling rather than the 0.5∘×0.5∘ Climatic Research Unit (CRU) T2 data. The novel data set, HySN, covering 1979 to 2017, is archived in Zenodo (https://doi.org/10.5281/zenodo.1970170). The HySN estimates, existing estimates from reanalysis data, post-processed reanalysis data, and Variable Infiltration Capacity (VIC) type forcing data are compared with observations from the Norwegian mainland from 1982 through 1999. Humidity measurements from 84 stations are used, and, by employing quality control routines and including agricultural stations, SW↓ observations from 10 stations are made available. Meanwhile, only two stations have observations of LW↓. Vertical gradients, differences when compared at common altitudes, daily correlations, sensitivities to air mass type, and, where possible, trends and geographical gradients in seasonal means are assessed. At individual stations, differences in seasonal means from the observations are as large as 7 ∘C for dew point temperature, 62 W m−2 for SW↓, and 24 W m−2 for LW↓. Most models overestimate SW↓ and underestimate LW↓. Horizontal resolution is not a predictor of the model's efficiency. Daily correlation is better captured in the products based on newer reanalysis data. Certain model estimates show different dependencies on geographical features, diverging trends, or a different sensitivity to air mass type than the observations.

Ozone and carbon monoxide observations over open oceans on R/V &amp;lt;i&amp;gt;Mirai&amp;lt;/i&amp;gt; from 67° S to 75° N during 2012 to 2017: testing global chemical reanalysis in terms of Arctic processes, low ozone levels at low latitudes, and pollution transport

Abstract. Constraints from ozone (O3) observations over oceans are needed in addition to those from terrestrial regions to fully understand global tropospheric chemistry and its impact on the climate. Here, we provide a large data set of ozone and carbon monoxide (CO) levels observed (for 11 666 and 10 681 h, respectively) over oceans. The data set is derived from observations made during 24 research cruise legs of R/V Mirai during 2012 to 2017, in the Southern, Indian, Pacific, and Arctic oceans, covering the region from 67∘ S to 75∘ N. The data are suitable for critical evaluation of the over-ocean distribution of ozone derived from global atmospheric chemistry models. We first give an overview of the statistics in the data set and highlight key features in terms of geographical distribution and air mass type. We then use the data set to evaluate ozone mixing ratio fields from the tropospheric chemistry reanalysis version 2 (TCR-2), produced by assimilating a suite of satellite observations of multiple species into a global atmospheric chemistry model, namely CHASER. For long-range transport of polluted air masses from continents to the oceans, during which the effects of forest fires and fossil fuel combustion were recognized, TCR-2 gave an excellent performance in reproducing the observed temporal variations and photochemical buildup of O3 when assessed from ΔO3∕ΔCO ratios. For clean marine conditions with low and stable CO mixing ratios, two focused analyses were performed. The first was in the Arctic (&gt; 70∘ N) in September every year from 2013 to 2016; TCR-2 underpredicted O3 levels by 6.7 ppbv (21 %) on average. The observed vertical profiles from O3 soundings from R/V Mirai during September 2014 had less steep vertical gradients at low altitudes (&gt; 850 hPa) than those obtained by TCR-2. This suggests the possibility of a more efficient descent of the O3-rich air from above than assumed in the models. For TCR-2 (CHASER), dry deposition on the Arctic ocean surface might also have been overestimated. In the second analysis, over the western Pacific equatorial region (125–165∘ E, 10∘ S to 25∘ N), the observed O3 level more frequently decreased to less than 10 ppbv in comparison to that obtained with TCR-2 and also those obtained in most of the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) model runs for the decade from 2000. These results imply loss processes that are unaccounted for in the models. We found that the model's positive bias positively correlated with the daytime residence times of air masses over a particular grid, namely 165–180∘ E and 15–30∘ N; an additional loss rate of 0.25 ppbv h−1 in the grid best explained the gap. Halogen chemistry, which is commonly omitted from currently used models, might be active in this region and could have contributed to additional losses. Our open data set covering wide ocean regions is complementary to the Tropospheric Ozone Assessment Report data set, which basically comprises ground-based observations and enables a fully global study of the behavior of O3.