Elevated Inversion Research Articles

Effects of aerosols on the atmospheric boundary layer temperature inversion over the Sichuan Basin, China

The relationship between the aerosol and the boundary layer temperature inversion is analyzed based on the radiosonde, visibility, and PM2.5 mass concentration data from 2014 to 2016 in the wintertime over the Sichuan Basin. The radiosonde data are divided into four equal parts according to the previous 12-h average visibility and PM2.5 mass concentration. The mechanisms of the aerosol radiative effect on the boundary layer temperature inversion are further investigated by using the radiometer, the Mie scattering lidar, and the microwave radiometer in Chengdu. 1D-SBDART simulation is performed to better clarify the mechanisms. The occurrence probability of multi-layer temperature inversions is about 46.86% in winter over the Sichuan Basin. As the PM2.5 mass concentration increases (visibility decreases), the surface-based inversion frequency increases more consistently in the morning, while the elevated inversion increases more consistently in the evening. Aerosols can enhance the boundary layer temperature inversion at both daytime and nighttime due to the radiative effect, while clouds mitigate the enhancement by aerosol effects. The simulation results show that: from clean to heavy pollution conditions, in clear-sky the surface shortwave radiation reduces by 135.04 w·m−2 and the heating rate increases by 0.75 k·d−1; in cloudy sky the surface shortwave radiation reduces by 46.15 w·m−2 and the heating rate increases by 0.35 k·d−1. The case in Chengdu from 08:00 BJT on December 6 to 08:00 on December 10 in 2016 well illustrates the mechanisms.

Elevation Spatial Variation Error Compensation in Complex Scene and Elevation Inversion by Autofocus Method in GEO SAR

Due to the high altitude of geosynchronous synthetic aperture radar (GEO SAR), its synthetic aperture time can reach up to several hundred seconds, and its revisit cycle is very short, which makes it of great application worth in the remote sensing field, such as in disaster monitoring and vegetation measurements. However, because of the elevation of the target, elevation spatial variation error is caused in the GEO SAR imaging. In this paper, we focus on the compensation of the elevation space-variant error in the fast variant part with the autofocus method and utilize the error to carry out elevation inversing in complex scenes. For a complex scene, it can be broken down into a slow variant slope and the remaining fast variant part. First, the phase error caused by the elevation spatial variation is analyzed. Second, the spatial variant error caused by the slowly variant slope is compensated with the improved imaging algorithm. The error caused by the remaining fast variable part is the focus of this paper. We propose a block map-drift phase gradient autofocus (block-MD-PGA) algorithm to compensate for the random phase error part. By dividing sub-blocks reasonably, the elevation spatial variant error is compensated for by an autofocus algorithm in each sub-block. Because the errors of different elevations are diverse, the proposed algorithm is suitable for the scene where the target elevations are almost the same after the sub-blocks are divided. Third, the phase error obtained by the autofocus method is used to inverse the target elevation. Finally, simulations with dot-matrix targets and targets based on the high-resolution TerraSAR-X image verify the excellent effect of the proposed method and the accuracy of the elevation inversion.

DETERMINATION OF THE CHARACTERISTICS OF INVERSION REFLECTING LAYERS IN THE TROPOSPHERE ON CHANGES IN THE SIGNAL INTENSITY ON THE NEAR-EARTH OVER-THE-HORIZON ROUTES IN THE MIDDLE LATITUDES

The methodology for determining changes of altitude, elevation velocity, and reflection coefficient of the elevated inversion layer in the troposphere is examined based on the results of observation of VHF signals on over-the-horizon (OTH) routes. Estimations of the elevation velocity and reflection coefficient of the elevated inversion layers on the results of measuring of the levels of VHF signals in the zone of the near geometric shadow in the middle latitudes and the meteorological sounding data using balloons are obtained.

Accuracy analysis of multi-baseline InSAR height inversion

Digital elevation model (DEM) is of great significance in commercial and scientific applications, and the accuracy of elevation inversion represents the quality of DEM. With reference to the height measurement accuracy formula of single-baseline interferometric SAR, the mathematical relations between elevation accuracy and platform height, lower viewing angle, target oblique distance, baseline strip number, baseline length and baseline roll angle are established, and the variation of elevation accuracy with system parameters (especially the number of base lines and baseline length) is quantitatively analyzed, and the optimal range of multi-baseline InSAR system parameters is obtained. It provides a theoretical basis for the optimal design of system parameters.

The topography of the Iberian Peninsula from integrated geophysical-petrological multi-data inversion

The topography of the Iberian Peninsula is characterized by the presence of Variscan and Alpine orogenic belts and foreland basins, but what sets it apart from the rest of Western Europe are the large elevated flat surfaces (700 m above sea-level on average) in its central parts. The origin and support of such high average topography, whether isostatic or dynamic in nature, is a matter of intense debate. To understand Iberian topography, it is key to have a reliable image of the present-day lithospheric thermochemical structure. So far, this structure remains poorly constrained, particularly at mantle level. The goal of this paper is to derive robust estimates of the thermal, compositional and density structure of the lithosphere beneath the Iberian Peninsula from an integrated geophysical-petrological probabilistic inversion of surface wave, elevation, geoid anomaly and heat flow data. Our inversion reveals an average lithospheric thickness of 80–100 km in the Iberian Peninsula with only moderate lateral variations. The most prominent lithospheric thickness change is a steep decrease from the central to the easternmost Pyrenees. The thinnest lithosphere in our models is found below the south-eastern Mediterranean margin (<80 km), overlapping with the Neogene Tallante-Cabo de Gata volcanic fields. The present-day thermochemical structure reveals a clear imprint of the geodynamic evolution of Iberia. Lithospheric thickness and, therefore, lithospheric geotherms are to a large extent related to Alpine Cenozoic compression and extension. The western Pyrenees and Iberian chains seem to have been affected by Mesozoic rifting processes that imprinted a fertile signature into the originally more refractory Variscan Iberian lithosphere. In the Betic domain to the south, the lithospheric thermochemical structure is likely conditioned by the ongoing Alboran subduction. Except for the Mediterranean margin, where we find evidence for moderate negative dynamic topography, most of the surface elevation in Iberia can be explained by lateral density contrasts associated with variations in crustal and lithospheric thickness and lithology.

WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data

SUMMARYWe present a new global thermochemical model of the lithosphere and underlying upper mantle constrained by state of the art seismic waveform inversion, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data: WINTERC-G. The model is based upon an integrated geophysical–petrological approach where seismic velocities and density in the mantle are computed within a thermodynamically self-consistent framework, allowing for a direct parametrization in terms of the temperature and composition variables. The complementary sensitivities of the data sets allow us to constrain the geometry of the lithosphere–asthenosphere boundary, to separate thermal and compositional anomalies in the mantle, and to obtain a proxy for dynamic surface topography. At long spatial wavelengths, our model is generally consistent with previous seismic (or seismically derived) global models and earlier integrated studies incorporating surface wave data at lower lateral resolution. At finer scales, the temperature, composition and density distributions in WINTERC-G offer a new state of the art image at a high resolution globally (225 km average interknot spacing). Our model shows that the deepest lithosphere–asthenosphere boundary is associated with cratons and, also, some tectonically active areas (Andes, Persian Gulf). Among cratons we identify considerable differences in temperature and composition. The North American and Siberian Cratons are thick (&amp;gt;260 km) and compositionally refractory, whereas the Sino-Korean, Aldan and Tanzanian Cratons have a thinner, fertile lithosphere, similar to younger continental lithosphere elsewhere. WINTERC-G shows progressive thickening of oceanic lithosphere with age, but with significant regional differences: the lithospheric mantle beneath the Atlantic and Indian Oceans is, on average, colder, more fertile and denser than that beneath the Pacific Ocean. Our results suggest that the composition, temperature and density of the oceanic mantle lithosphere are related to the spreading rate for the rates up to 50–60 mm yr–1: the lower spreading rate, the higher the mantle fertility and density, and the lower the temperature. At greater spreading rates, the relationship disappears. The 1-D radial average of WINTERC-G displays a mantle geothermal gradient of 0.55–0.6 K km–1 and a potential temperature of 1300–1320 °C for depths &amp;gt;200 km. At the top of the mantle transition zone the amplitude of the maximum lateral temperature variations (cratons versus hotspots) is about 120 K. The isostatic residual topography values, a proxy for dynamic topography, are large (&amp;gt;1 km) mostly in active subduction settings. The residual isostatic bathymetry from WINTERC-G is remarkably similar to the pattern independently determined based on oceanic crustal data compilations. The amplitude of the continental residual topography is relatively large and positive (&amp;gt;600 m) in the East European Craton, Greenland, and the Andes and Himalayas. By contrast, central Asia, most of Antarctica, southern South America and, to a lesser extent, central Africa are characterized by negative residual topography values (&amp;gt;–400 m). Our results show that a substantial part of the topography signal previously identified as residual (or dynamic) is accounted for, isostatically, by lithospheric density variations.

Characteristics of low-level temperature inversions over the Arctic Ocean during the CHINARE 2018 campaign in summer

Across the Arctic Ocean, the semi-permanent sea-ice layer insulates the atmosphere from the Arctic Ocean, thereby influencing the lower boundary conditions of the atmosphere in this region. The presence of a temperature inversion predominantly characterizes the Arctic lower troposphere throughout the year. The 9th Chinese National Arctic Research Expedition took place in the Pacific Sectors of the Arctic Ocean from July to September 2018, gathering high-resolution radiosonde data to provide a detailed structure of the low-level temperature inversion (LLI) over the summer months. Statistical analyses showed that LLIs occurred most frequently below 500m and were generally weaker and shallower than those occurring during the winter months. Low-level inversions are influenced by both local meteorology and large scale synoptic conditions. The continual presence of low-level clouds or fog tends to lift the inversion layer at the local scale, transferring it from a surface-based inversion (SBI) to an elevated inversion (EI). By contrast, SBIs were found to dominate over regions of melting sea-ice. Regimes, where the cloud top penetrated the inversion base were more frequently observed than cloud capped by inversion regimes. Inversions tended to be deeper, stronger, and with a lower base during cloud top penetrating inversion base regimes. At the synoptical scale, the intense poleward intrusions of warm air brought moist air to the top of low-level inversions, creating a robust thermal stratification between layers and promoting extensive and frequency occurrences of low cloud/fog. Moreover, the polar high contributed to establishing a multilayer inversion structure at relatively high altitudes by subsidence. These findings contribute to an improving understanding of low-level vertical temperature structures and their influence on a rapidly warming Arctic.

The impacts of the atmospheric boundary layer on regional haze in North China

An intensive atmospheric boundary layer (ABL) experiment was conducted simultaneously at six stations arranged in a cross shape on the North China Plain (NCP) from 26 November to 26 December 2019. The impacts of the regional ABL structure on heavy haze pollution and the relationship between the ABL height and aerosol accumulation layer (AAL) depth were discussed. Bouts of downdrafts generate a persistent descending elevated inversion layer, helping the maintenance and exacerbation of haze pollution. Continuous weak wind layers contribute to the pollutants accumulation, and low-level jets promote the removal of air pollutants. The unique landform conditions of the NCP are reflected in its regional ABL structure and further affect the spatial distribution of haze pollution. Due to the drainage flow and strong downdrafts, the western stations near the mountains have a colder surface and warmer upper air masses, resulting in a more stable stratification and worse diffusion conditions; these stations also experience a thicker weak wind layer caused by increased friction. Thus, the spatial distribution of haze is heavier in the west and lighter in the east. The convective boundary layer (CBL) height declines evidently during haze episodes, usually lower than 560 m. Furthermore, as the vertical distribution of aerosols is mainly influenced by daytime thermal turbulence and maintained at night, it is appropriate to determine the CBL height using the AAL depth. However, the AAL depth is not consistent with the stable boundary layer height due to the influence of the residual layer at night.

Vertical structures of temperature inversions and clouds derived from high-resolution radiosonde measurements at Ny-Ålesund, Svalbard

The knowledge of the vertical atmospheric structures in the Arctic Region remains elusive, due largely to sparse long-term continuous profiling observations. Based on the temporally high-resolution (1 s) radiosonde measurements from April 2017 to September 2019 collected at the Ny-Ålesund (11.92°E, 78.92°N) station in the Arctic, we analyzed the characteristics of temperature inversion (TI) and clouds, including the diurnal and seasonal variabilities under different atmospheric circulations. Clouds mainly appear in the lower troposphere, with the largest contribution by double-layer clouds. The seasonal variation of vertical cloud distribution above 7 km seems is closely linked to the seasonal variability of tropopause height. Besides, the diurnal variation of TI frequency exhibits significant seasonality, with a bimodal distribution in the vertical, with stronger TI intensity in summer. The lowest temperatures at the top of bottom of the elevated inversion are observed in winter, whereas the lowest temperature of the surface-based inversion top is observed in spring, which may be related to the seasonal variation of sea surface temperature. The characteristics of cloud and TI are further analyzed under the five typical circulation patterns. It is found that the low-pressure system and southerly wind in front of the trough are favorable for cloud formation in the lower troposphere, while the impact of synoptic pattern on clouds in the upper troposphere seems negligible, likely due to the cold environment. The TI associated with cyclone systems tends to be much thinner and weaker, owning to the conditionally unstable conditions. These findings provide key reference for the vertical structure of the inversion and cloud in the Arctic, which is expected to help improve cloud parameterization in numeric model.

Temperature inversions in China derived from sounding data from 1976 to 2015

Temperature inversions inhibit the transfer of momentum, heat and moisture in the atmosphere and have led to severe air pollution in China. This study investigated the spatiotemporal variation in temperature inversions in China using sounding data for the past four decades. Surface-based inversion, elevated inversion, and both in one sounding dataset were analysed. Statistical analyses of inversion parameters included frequency, strength and depth. The annual frequency of total inversions showed no significant increasing or decreasing trend with mean values of 0.78, 0.33, 0.24, 0.28, 0.5 and 0.36 at six stations representing different climate zones—Beijing, Harbin, Haikou, Shaowu, Ruoqiang, and Xining, respectively. The annual inversion strength and depth showed downward trends. Monthly variation in inversion frequency and strength differed among stations. The weakest surface-based inversion was found in summer at Beijing and Harbin with mean values of 1 and 1.3 °C, respectively; the strongest surface-based inversion was found in winter with respective mean values of 3.5 and 3.6 °C. Higher surface temperature in summer and subsidence aloft in winter may explain the monthly variation in inversion depth with a minimum in summer, with mean values of 165, 334, 135, 267, 363 and 420 m, and a maximum in winter, with mean values of 250, 646, 140, 591, 806 and 664 m, at the six respective stations. Total inversion was least frequent in southwestern China (mean 0.15), surface-based inversion was most frequent in the north (mean 0.78), and elevated inversion was most frequent in the southeast (mean 0.42). The strongest, deepest surface-based inversion dominated in the north (mean 3.4 °C and 398 m). Elevated inversion strength did not significantly differ among regions (mean 2.5 °C). The deepest elevated inversion dominated in the southeast (mean 654 m). Future efforts should focus on the interactions between aerosols and temperature inversions and accurate model simulations of temperature inversions.

A Novel Airborne Dual-Antenna InSAR Calibration Method for Backprojection Imaging Model

The interferometric synthetic aperture radar (InSAR) elevation inversion method based on the backprojection (BP) imaging model simplifies the interferometric processing chain where image registration and phase unwrapping are not required. Meanwhile, BP algorithm is suitable for radar with different imaging modes and geometry. However, the existing calibration methods are all aimed at traditional InSAR which adopts frequency domain imaging algorithm, but the calibration method for backprojection InSAR elevation inversion model has not been published. In this paper, we propose a novel InSAR calibration method which combines Fast Fourier Transform (FFT) estimation method with sensitivity equation method based on backprojection imaging model. FFT is used to process the interferometric phase which has removed the terrain phase of external digital elevation model (DEM) under BP imaging, and the estimation of interferometric parameters is realized through the phase fringe frequency. In the calibration method based on sensitivity equations, the deviations of interferometric parameters are calculated by solving sensitivity equations according to the three-dimensional information of ground control points. FFT estimation method not only generates the initial baseline parameters for sensitivity equation method, which is conducive to obtaining the global optimal solution, but also separates the calibration of phase offset and baseline parameters, which makes it possible to minimize the condition number of sensitivity matrix in sensitivity equation method. Finally, we obtain the calibrated interferometric parameters through iteration of sensitivity equation method and realize high accuracy DEM inversion. Both simulation experiment and airborne dual-antenna InSAR data processing are performed to verify the effectiveness of this method.

Warm-Air Advection Over Melting Sea-Ice: A Lagrangian Case Study

Observations from the 2014 Arctic Clouds in Summer Experiment indicate that, in summer, warm-air advection over melting sea-ice results in a strong surface melting feedback forced by a very strong surface-based temperature inversion and fog formation exerting additional heat flux on the surface. Here, we analyze this case further using a combination of reanalysis dataset and satellite products in a Lagrangian framework, thereby extending the view spatially from the local icebreaker observations into a Langrangian perspective. The results confirm that warm-air advection induces a positive net surface-energy-budget anomaly, exerting positive longwave radiation and turbulent heat flux on the surface. Additionally, as warm and moist air penetrates farther into the Arctic, cloud-top cooling and surface mixing eventually erode the surface inversion downstream. The initial surface inversion splits into two elevated inversions while the air columns below the elevated inversions transform into well-mixed layers.

Thermal Inversion and Particulate Matter Concentration in Wrocław in Winter Season

Studies on air quality frequently adopt clustering, in particular the k-means technique, owing to its simplicity, ease of implementation and efficiency. The aim of the present paper was the assessment of air quality in a winter season (December–February) in the conditions of temperature inversion using the k-means method, representing a non-hierarchical algorithm of cluster analysis. The air quality was assessed on the basis of the concentrations of particulate matter (PM10, PM2.5). The studies were conducted in four winter seasons (2015/16, 2016/17, 2017/18, 2019/20) in Wrocław (Poland). As a result of the application of the v-fold cross test, six clusters for each fraction of PM were identified. Even though the analysis covers only four winter seasons, the applied method has unequivocally revealed that the characteristics of surface-based (SBI) and elevated inversions (ELI) affect the concentration level of both fractions of particulate matter. In the case of PM10, the average lowest daily concentration (15.5 µg·m−3) was recorded in the conditions of approx. 205 m in thickness, 0.5 °C intensity of the SBI and at the height of the base of the ELI at approx. 1700 m a.g.l., a thickness of 148 m and an intensity of 1.2 °C. In turn, the average highest concentration (136 µg·m−3) was recorded at a thickness of SBI of approx. 400 m and an intensity of 1.4 °C. Such high concentration occurred when the lowest location of ELI formed at 764 m a.g.l. with a thickness of 308 m and an intensity of 0.96 °C. A marked role of the thickness of the SBI and ELI as well as the height of the base of the lowest location of ELI was also manifested with respect to PM2.5 concentrations.

The Climatology of Lower Tropospheric Temperature Inversions in China from Radiosonde Measurements: Roles of Black Carbon, Local Meteorology, and Large-Scale Subsidence

AbstractThe variability of the lower tropospheric temperature inversion (TI) across China remains poorly understood. Using seven years’ worth of high-resolution radiosonde measurements at 120 sites, we compile the climatology of lower tropospheric TI in terms of frequency, intensity, and depth during the period from 2011 to 2017. The TI generally exhibits strong seasonal and geographic dependencies. Particularly, the TI frequency is found to be high in winter and low in summer, likely due to the strong aerosol radiative effect in winter. The frequency of the surface-based inversion (SBI) exhibits a “west low, east high” pattern at 0800 Beijing time (BJT), which then switches to “west high, east low” at 2000 BJT. Both the summertime SBI and elevated inversion (EI) reach a peak at 0800 BJT and a trough at 1400 BJT. Interestingly, the maximum wintertime EI frequency occurs over Southeast China (SEC) rather than over the North China Plain (NCP), likely attributable to the combination of the heating effect of black carbon (BC) originating from the NCP, along with the strong subsidence and trade inversion in SEC. Correlation analyses between local meteorology and TI indicate that larger lower tropospheric stability (LTS) favors more frequent and stronger TIs, whereas the stronger EI under smaller LTS conditions (unstable atmosphere) is more associated with subsidence rather than BC. Overall, the spatial pattern of the lower tropospheric TI and its variability in China are mainly controlled by three factors: local meteorology, large-scale subsidence, and BC-induced heating. These findings help shed some light on the magnitude, spatial distribution, and underlying mechanisms of the lower tropospheric TI variation in China.

Regional Variability and Trends of Temperature Inversions in Greenland

AbstractStrong and thick temperature inversions are key components of the Arctic climate system and it is important to study and better understand them. The present study quantifies the temporal and spatial variability of surface-based inversions (SBIs) and elevated inversions (EIs) over Greenland, as derived from the ERA-Interim (ERA-I) dataset for the period 1979–2017. The seasonal and multiannual variability of inversion strength, thickness, and frequency are examined. Our results clearly show regional as well as seasonal patterns of both SBIs and EIs. SBIs are more frequent and stronger than EIs, and the spatial variability of inversions is larger during winter and smaller during summer. Furthermore, during summer, there has been a trend toward stronger (0.3 K decade−1), thicker (12 m decade−1), and more frequent (3% decade−1) SBIs in the southern part of Greenland, especially in the past two decades. Evidently, the strengthening of the anticyclone over Greenland causes a reduction of cloud cover, which manifests in an increase in SBI strength and thickness, particularly in the southern part of Greenland.

Temperature Inversion and Clouds Over the Arctic Ocean Observed by the 5th Chinese National Arctic Research Expedition

AbstractThe Arctic is of great significance to global weather and climate systems. However, its atmospheric conditions have yet to be fully understood, partly because of the lack of intensive observations. Here we reported on the characteristics of lower troposphere over the Arctic Ocean using high‐resolution radiosonde data collected during the 5th Chinese National Arctic Research Expedition from July to September 2014. Statistical analyses showed that temperature inversion (TI) occurred most frequently below 700 m, without apparent temporal variability between morning and noon. In contrast, the occurrence frequency of morning surface‐based inversion (SBI) was always higher than at noon in the whole boundary layer, whereas the elevated inversion (EI) frequency seemed much lower in the morning compared with at noon. More frequent deeper clouds tended to occur in the morning than at noon, which led to more frequent EI than SBI. SBI was found to dominate the clear‐sky condition, whereas EI was generally observed under cloudy conditions. Regarding the seasonal variation, deep TI and clouds dominated during the first intensive observational period (IOP‐1; July 21–31) because of warm advection in combination with heating effects induced by long‐range transported black carbon (BC). During IOP‐2 (August 1–18), synoptic scale subsidence prevailed, with frequent EI and SBI partly caused by BC accumulation over the Arctic Ocean. In comparison, more clouds and less TI occurred during IOP‐3 (August 27–September 11) largely due to the outbreaking polar vortex. These observations contribute to a better understanding of vertical temperature and cloud structures under global warming.

Representation of low-tropospheric temperature inversions in ECMWF reanalyses over Europe

Despite the fact that tropospheric temperature inversions are thought to be an important feature of climate as well as a significant factor affecting air quality, low-level cloud formation, and the radiation budget of the Earth, a quantitative assessment of their representation in atmospheric reanalyses is yet missing. Here, we provide new evidence of the occurrence of low-tropospheric temperature inversions and associated uncertainties in their parameters existing among reanalyses produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) and upper-air soundings for Europe covering the period 2001–2010. The reanalyses utilized here include (1) surface-input reanalyses represented by ERA-20C and CERA-20C as well as (2) full-input reanalyses represented by ERA-Interim and ERA5. The upper-air soundings were derived from the Integrated Global Radiosonde Archive (IGRA), version 2. The data consists mainly of air temperature and geopotential height from the model levels (ModLev) and pressure levels (PresLev) of ECMWF reanalyses. The results show that the frequency of surface-based inversions (SBI) and elevated inversions (EI) is largely in agreement among the reanalyses. The quality of their representation depends, however, on the inversion type, season, and region. Over the vast majority of IGRA upper-air stations, SBI frequency is overestimated and EI frequency is underestimated by ECMWF reanalyses. Substantially larger uncertainties arise from the selection between the data of ModLev and PresLev of the reanalyses—the differences in the frequency of the temperature inversions are particularly large for summertime SBI suggesting that PresLev are not capable of resolving the main features of shallow and weak SBI.

Temperature inversions in the atmospheric boundary layer and lower troposphere over the Sichuan Basin, China: Climatology and impacts on air pollution

The Sichuan Basin (SB) is one of the four most severely polluted regions in China in terms of air quality, and the frequent generation of temperature inversions is a key factor. The deep mountain-basin topography and the geographical location adjacent to the Tibetan Plateau combine to make the inversion characteristics of this region unique. Knowledge regarding these characteristics remains limited, however. In this study, the radiosonde data at standard pressure levels and significant levels from all SB operational radiosonde stations over 2015–2018 were used to document the climatological features of the inversions from the surface to a height of 5500 m and to evaluate the impact on local air pollutant concentrations.Results revealed that the temperature inversion in the SB is a common and year-round phenomenon. The annual inversion frequency, depth, and strength values are 74.4%, 252.2 m, and 1.3 °C/100 m, respectively. The inversions are most frequent (95.4%), deepest (289.4 m), and strongest (1.6 °C/100 m) in winter. They tend to occur at one of two heights, either below 600 m or between 2200 and 3500 m. Based on their bottom heights, the inversions were divided into three groups: surface-based inversions (SIs), elevated inversions (EIs), and lower-troposphere inversions (LTIs). Annual LTI is most frequent (63.0%) and deepest (264.7 m), while annual SI is strongest (1.8 °C/100 m). Extreme contrasts exist in the seasonal properties of different inversion types. All types of inversions play a considerable role in air pollution, resulting in a high probability of severe and very serious pollution in winter. SI has a greater impact on pollutant concentrations than EI and LTI. The frequent generation of LTIs is a unique feature of the deep SB. LITs exert a significant impact on the formation of local heavy air pollution, but have not been given sufficient attention.

Climatology of extreme downslope windstorms in the Russian Arctic

This paper presents the climatology of downslope windstorms in the Russian Arctic – bora on Novaya Zemlya, windstorms on Spitsbergen, in Tiksi and Pevek, bora on Wrangel Island – in connection with the large-scale circulation. Statistical analysis of wind speed and air temperature during windstorms, the frequency of the phenomenon, as well as analysis of trends in frequency and intensity of downslope windstorms in the late 20th and early 21st centuries were carried out. Similarity of the large-scale background (incoming) flow is evident for all regions; the most frequent features of the incoming flow are elevated inversion and low-tropospheric jet stream. The observed transformation of the incoming flow from weak to strong windstorm along with the relatively weak linear correlation between downslope wind speed and upwind-side flow characteristics suggest that there are nonlinear connections between windstorms and the incoming flow. We found significant negative trends in Wrangel Island bora frequency and intensity, connected largely with the Arctic circulation variability and associated sea-ice loss. A negative trend in intensity of windstorms was also found in Tiksi and Pevek, associated more with midlatitudes circulation patterns.

The Effect of Simple Vertical Fraction on Diffusion Equation with Deposition

The vertical fraction variation of eddy diffusivity was taking into consideration in the dispersion of pollutants from a point source. A power-law profile was used to describe the variation of wind speed and vertical eddy diffusivity with height z above ground surface. The dry deposition of the diffusing particles at the ground surface is taken into account through the boundary conditions. The concentration of pollutants was derived assuming that the vertical diffusion is limited by an elevated inversion layer located at the top of the boundary layer “h”. Also the decay distance of a pollutant along the wind direction was estimated. The resulting analytical solutions have been applied on the emission from the Research Reactor at Inshas in unstable condition and Hanford diffusion experiment in stable condition. Comparisons between proposed and observed concentrations show a good agreement between the proposed and observed concentrations when α=0.81 than others fractions and integer value. The results are discussed and presented in illustrative figures.