Altitude Dependence Research Articles

Dynamics of air temperature changes in the atmospheric boundary layer during the solar eclipse of March 29, 2006

The data of measurements of air temperature profiles in the atmospheric boundary layer (ABL) during the total solar eclipse on March 29, 2006 in Kislovodsk and at the Kislovodsk High-Mountain Scientific Station (KVNS) on the central shadow line are presented. The solar eclipse lasted from 14:08 to 16:27 local time, the total phase of the eclipse began at 15:15 and lasted 2:32. In development of the results obtained by us in our previous work, we compared the data on air temperature profiles at two points, Kislovodsk and KVNS. The influence of local conditions has been studied. It was shown that local conditions significantly affect both the amplitude of atmospheric pressure pulsations caused by a solar eclipse and their phase, as well as the nature of the change in the spectral density of air temperature with height in the range of periods corresponding to the duration of the solar eclipse. Based on the measurements of temperature profiles, the fluctuations of the atmospheric pressure difference at the level of the earth’s surface and at a certain height, up to which the temperature profiles were measured equal to 600 m, were reconstructed, caused by a solar eclipse, in coordinates: height – time has different trajectories in the case of Kislovodsk and KVNS. The difference in the trajectories of air temperature minima in Kislovodsk and at the KVNS determines both different delays in pressure minima relative to the beginning of the eclipse and time delays between surface pressure fluctuations at observation points as a whole. Also, a new method is proposed for determining the speed of ascending air currents using data on the altitude dependence of the time of reaching a minimum in temporal temperature variations caused by a solar eclipse. The changes in the spectral density of air are compared with height, the amplitude of the reconstructed atmospheric pressure pulsations in Kislovodsk and at the KVNS, and the speed of ascending air currents.

Spatial variability in the seasonal precipitation lapse rates in complex topographical regions – application in France

Abstract. Seasonal precipitation estimation in ungauged mountainous areas is essential for understanding and modeling a physical variable of interest in many environmental applications (hydrology, ecology, and cryospheric studies). Precipitation lapse rates (PLRs), defined as the increasing or decreasing rate of precipitation amounts with the elevation, play a decisive role in high-altitude precipitation estimation. However, the documentation of PLR in mountainous regions remains weak even though their utilization in environmental applications is frequent. This article intends to assess the spatial variability and the spatial-scale dependence of seasonal PLRs in a varied and complex topographical region. At the regional scale (10 000 km2), seven different precipitation products are compared in their ability to reproduce the altitude dependence of the annual/seasonal precipitation of 1836 stations located in France. The convection-permitting regional climate model (CP-RCM) AROME is the best in this regard, despite severe precipitation overestimation in high altitudes. The fine resolution of AROME allows for a precise assessment of the influence of altitude on winter and summer precipitation on 23 massifs at the sub-regional scale (∼ 1000 km2) and 2748 small catchments (∼ 100 km2) through linear regressions. With AROME, PLRs are often higher in winter at the catchment scale. The variability in the PLR is higher in high-altitude regions such as the French Alps, with higher PLRs at the border than inside the massifs. This study emphasizes the interest of conducting a PLR investigation at a fine scale to reduce spatial heterogeneity in the seasonal precipitation–altitude relationships.

ISSUES OF CREATING A SYSTEM FOR EARLY DETECTION OF FOREST FIRES BASED ON UNMANNED AERIAL VEHICLES

The urgent importance of the task of monitoring the state of forests lies in the danger of forest fires. Forest fires are a frequent occurrence in almost all continents. Despite the high information content of the spectral signs of a forest fire, the corresponding functionality is not fully used in the known implementations of the forest fire early detection system. The spectral region in which it is possible to distinguish forest areas in a state of fire from their usual state is quite wide and covers the middle and thermal zone of the infrared part of the spectrum. The installation of spectral equipment (multi- and hyperspectrometers) on board the UAV (unmanned aerial vehicle) can certainly expand the functionality of unmanned equipment in the early detection of forest fires. The optimal procedure for using UAVs equipped with hyperspectral equipment for early detection of forest fires is proposed. An optimization problem has been formulated and solved to determine the most appropriate mode of changing the UAV flight altitude with an increase in the wavelength of the measurements being carried out. According to the proposed method, on the right branch of the Planck curve, with increasing wavelength, the flight altitude should be increased, and on the left branch it should be reduced. This order corresponds to the case of increasing the wavelength on both branches and follows from the integral restriction set on the function of the dependence of the flight altitude on the wavelength, which comes from the limited real energy resources on board the UAV. Based on the developed method, a new technique for early detection of forest fires based on the use of hyperspectral method is proposed.

Quantum yields of CHDO above 300 nm

Abstract. The photolysis of mono-deuterated formaldehyde, CHDO, is a critical process in the deuterium enrichment of stratospheric hydrogen formed from methane. In this work, a consistent description of the quantum yields of the molecular and radical channels of the CHDO photolysis is deduced from literature data. The fluorescence measurements of Miller and Lee (1978) provided a first data set to deduce the product quantum yields. An alternative analysis is based on the measured quantum-yield spectrum for the radical channel of the CD2O photolysis by McQuigg and Calvert (1969), which is corrected for wavelength dependency and combined with the CH2O quantum-yield spectrum to provide an approximation for CHDO. Both approaches provide consistent results. Finally, the findings of Troe (1984, 2007) enable the specification of the pressure dependence of the quantum yield for CH2O and CD2O and, hence, for CHDO. We find that the radical channel does not show a pressure dependence, whereas the molecular channel is dominated by tunneling and quenching processes. Simplified representations are given that are readily implemented in kinetic atmospheric models. As an example of their application, the altitude dependence of the ratio of J(CHDO→HD+CO) and J(CH2O→H2+CO) is provided. Also, the importance of the photolysis of formaldehyde on the yield of HD in the atmosphere is shown through the altitudinal dependence of the isotopic fractionation.

A Deep-Learning Approach to a Volumetric Radio Environment Map Construction for UAV-Assisted Networks

Providing global coverage for ubiquitous users is a key requirement of the fifth generation (5G) and beyond wireless technologies. This can be achieved by integrating airborne networks, such as unmanned aerial vehicles (UAVs) and satellite networks, with terrestrial networks. However, the deployment of airborne networks in a three-dimensional (3D) or volumetric space requires a new understanding of the propagation channel and its losses in both the areal and altitude dimensions. Despite significant research on radio environment map (REM) construction, much of it has been limited to two-dimensional (2D) contexts. This neglects the altitude-related characteristics of electromagnetic wave propagation and confines REMs to 2D formats, which limits the comprehensive and continuous visualization of propagation environment variation in spatial dimensions. This paper proposes a volumetric REM (VREM) construction approach to compute 3D propagation losses. The proposed approach addresses the limitations of existing approaches by learning the spatial correlation of wireless propagation channel characteristics and visualizing REM in areal and height/altitude dimensions using deep learning models. Specifically, the approach uses two deep learning-based models: volume-to-volume (Vol2Vol) VREM with 3D-generative adversarial networks and sliced VREM with altitude-aware spider-UNets. In both cases, knowledge of the propagation environment and transmitter locations in 3D space is used to capture the spatial and altitude dependency of the propagation channel’s characteristics. We developed the Addis dataset, a large REM dataset comprising 54,000 samples collected from the urban part of Addis Ababa, Ethiopia, to train the proposed models. Each sample of data comprises a 512-meter by 512-meter areal resolution with different 3D obstacles (buildings and terrain), 15 simulated propagation loss maps at every 3-meter altitude resolution, and 80 different 3D transmitter locations. The results of the training and testing of the proposed models reveal that the constructed VREMs are statistically comparable. In particular, the Vol2Vol approach has a minimum L1 loss of 0.01, which further decreases to 0.0084 as the line-of-sight (LoS) probability increases to 0.95.

Vertical characteristics of temperature and relative humidity during the spring continuous warming processes in Altay, Xinjiang of China

To understand the triggering conditions of snowmelt floods in northern Xinjiang, China, the diurnal evolution and altitude dependence characteristics of spring temperature and relative humidity (RH) are investigated, particularly placing emphasis on continuous warming process, mainly based on the data collected from the densely sounding experiment at Altay Station in spring 2021. The results show that the mean maximum and minimum temperature respectively occur at nightfall and sunrise, the mean RH below 2,000 m is the highest at sunrise and the lowest at nightfall, and the mean RH above 5,000 m is the highest at sunrise and the lowest at midday. The mean RH value climbs up first but goes down later, and the largest mean RH is within the height range of 2,500–5,000 m. The radiation inversion with the depth of 660 m tends to occur frequently at midnight and around sunrise, and it does not exist when the continuous warming process sets out but gradually develops with the advancing process. During the continuous warming processes, there exists an unsynchronized warming from the ground to the upper air. The upper-air warming lags behind that on the ground for 2–5 d, and then it continues the trend. Below 2,000 m, accompany with the advance of the warming processes, the RH keeps at relatively low level and changes small along height after the first 2–3 days, when the max RH drop swiftly from 80%–98% to less than 25% and tend to be consistent at the four observation times. The trough and ridge systems responsible for the continuous warming processes in early and middle spring are mainly the deep long-wave system, but in the middle and late spring, the adjustment speed of the trough and ridge systems are accelerated and more short-wave activities fuel the continuous warming.

Impact of Biomass Burning Organic Aerosol Volatility on Smoke Concentrations Downwind of Fires.

Biomass burning particulate matter (BBPM) affects regional air quality and global climate, with impacts expected to continue to grow over the coming years. We show that studies of North American fires have a systematic altitude dependence in measured BBPM normalized excess mixing ratio (NEMR; ΔPM/ΔCO), with airborne and high-altitude studies showing a factor of 2 higher NEMR than ground-based measurements. We report direct airborne measurements of BBPM volatility that partially explain the difference in the BBPM NEMR observed across platforms. We find that when heated to 40-45 °C in an airborne thermal denuder, 19% of lofted smoke PM1 evaporates. Thermal denuder measurements are consistent with evaporation observed when a single smoke plume was sampled across a range of temperatures as the plume descended from 4 to 2 km altitude. We also demonstrate that chemical aging of smoke and differences in PM emission factors can not fully explain the platform-dependent differences. When the measured PM volatility is applied to output from the High Resolution Rapid Refresh Smoke regional model, we predict a lower PM NEMR at the surface compared to the lofted smoke measured by aircraft. These results emphasize the significant role that gas-particle partitioning plays in determining the air quality impacts of wildfire smoke.

Inferring the photolysis rate of NO2 in the stratosphere based on satellite observations

Abstract. NO and NO2 (NOx) play major roles in both tropospheric and stratospheric chemistry. This paper provides a novel method to obtain a global and accurate photolysis rate for NO2 based on satellite data. The photolysis rate J(NO2) dominates the daytime diurnal variation of NOx photochemistry. Here the spatial variation of J(NO2) at 50–90∘ S in December from 20–40 km is obtained using data from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment. Because NO and NO2 rapidly exchange with one another in the daytime, J(NO2) can be attained assuming steady state, and the results are shown to be consistent with model results. The J(NO2) value decreases as the solar zenith angle increases and has a weak altitude dependence. A key finding is that satellite-derived J(NO2) increases in the polar regions, in good agreement with model predictions, due to the effects of ice and snow on surface albedo. Thus, the method presented here provides an observation-based check on the role of albedo in driving polar photochemistry.

Assessment of climate simulation over the Tibetan Plateau based on high-resolution multi-RCM within CORDEX-EA-II

The climate simulation over the Tibetan Plateau (TP) remains a challenge for climate models, limiting the reliability of future climate projections over there. This study focuses on the performance of five regional climate models (RCMs) under the Coordinated Regional Climate Downscaling Experiment-East Asia (CORDEX-EA-II) in reproducing the climate over the TP for the period 1981–2015. All simulations are driven by ERA-Interim reanalysis at a resolution of 25 km (0.22°), and are evaluated against the two observation datasets (CN05 and ERA5) as well as inter-compared to identify their weaknesses and differences among them. The results show that all RCMs can capture the observed spatial distribution and annual cycle of temperature and precipitation over the TP, with overall cold and wet biases. The cold biases exhibit a clear altitude dependence, while there is no obvious relationship between precipitation biases and altitude, and most of the RCMs advance the time with the maximum monthly precipitation by 1 month over the northwestern TP. The distribution of temperature trends and the signal of elevation-dependent warming in the observation are well reproduced by most of the RCMs. Inconsistent precipitation trends are found between the two observational datasets during summer and autumn, and the simulated precipitation trends are more consistent with that in ERA5 than in CN05. Further analysis suggests that the downward shortwave radiation is the main contributor to the diverse temperature simulations among the RCMs for all seasons, and the inability of RCMs to reproduce the precipitation trends may be related to the misrepresentation of convection processes. Moreover, some of the RCMs perform better than ERA5 over the TP, demonstrating the importance of dynamical downscaling over the TP.

Dusty plasmas above the sunlit surface of Mercury

Above the sunlit surface of Mercury, the properties and formation of dusty plasmas are investigated. It is demonstrated that the dusty plasmas are formed for subsolar angles exceeding approximately 76° due to photoelectric and electrostatic processes. As a result, the dusty plasmas are present in the polar regions of Mercury, characterized by latitudes of about 70° and above. The formation of dusty plasmas is also possible for lower latitudes, but only where the surface profile allows it. Plasmas above the sunlit surface of Mercury consist, in particular, of photoelectrons, electrons, and ions of the solar wind, and also charged dust particles. The distribution functions of photoelectrons near the surface of Mercury, as well as the altitude dependences of the number densities of dust particles, their charges and sizes, as well as electric fields, are obtained. The calculations are carried out which correspond to the position of Mercury at aphelion and perihelion of its orbit for the situations of dusty plasma location in the vicinity of magnetic poles of Mercury and in other regions. It is shown that there are qualitative differences between the dusty plasma systems of Mercury and the Moon related to the fact that Mercury has a magnetosphere and Mercury's orbit is one of the most eccentric of all planetary orbits in the Solar System. The effects of magnetic fields can slightly influence the dust particle transport and, correspondingly, the expansion of the region of the existence of dusty plasmas above the surface of Mercury due to the effect of dust particle transport is not so significant as at the Moon. Furthermore, due to the presence of Mercury's magnetosphere, the solar wind is important for the formation of dusty plasmas at Mercury only in the vicinity of the regions of the magnetic poles. In other regions of Mercury, in contrast to the situation at the Moon, the solar wind does not influence significantly the dusty plasma properties. The dusty plasma parameters are different in the cases of aphelion and perihelion of the orbit of Mercury.

Composition and Concentration of the Biogenic Components of the Aerosols Collected over Vasyugan Marshes and Karakan Pine Forest at Altitudes from 500 to 7000 m

The purpose of this study was to compare the concentration of total protein, as well as the composition and abundance of culturable microorganisms in atmospheric aerosols collected over the Vasyugan marshes and the Karakan pine forest during a flight in September 2018 at altitudes from 500 to 7000 m. The determined concentrations of total protein in Karakan samples were on average much less than those for the same area in September of other years. The concentration and composition of microorganisms in aerosol samples were determined by cultural methods and isolate genotyping. Altitude dependences of concentrations of total protein and culturable microorganisms were revealed. A rather stable altitude profile of culturable microorganism concentration was found over the Vasyugan marshes. No microorganisms were found at altitudes 4000 and 5500 m over the Karakan pine forest. Non-spore-bearing and spore-forming bacteria, as well as molds and yeast-like fungi, were isolated from aerosol samples. A high concentration of cosmopolitan psychrotolerant yeast Aureobasidium, capable of causing severe mycoses, and opportunistic bacteria Acinetobacter were found. A great similarity of composition and an atypically high abundance of non-spore-bearing bacteria and psychrotolerant yeast-like fungi were revealed in samples taken at altitudes of 1000 and 500 m in both studied regions, which may be a consequence of large-scale horizontal transport of layers of atmospheric air contaminated with microorganisms.

A Bayesian hierarchical spatio-temporal model for extreme temperatures in Extremadura (Spain) simulated by a Regional Climate Model

A statistical study was made of the temporal trend in extreme temperatures in the region of Extremadura (Spain) during the period 1981–2015 using a Regional Climate Model. For this purpose, a Weather Research and Forecasting (WRF) Regional Climate Model extreme temperature dataset was obtained. This dataset was then subjected to a statistical study using a Bayesian hierarchical spatio-temporal model with a Generalized Extreme Value (GEV) parametrization of the extreme data. The Bayesian model was implemented in a Markov chain Monte Carlo framework that allows the posterior distribution of the parameters that intervene in the model to be estimated. The role of the altitude dependence of the temperature was considered in the proposed model. The results for the spatial-trend parameter lend confidence to the model since they are consistent with the dry adiabatic gradient. Furthermore, the statistical model showed a slight negative trend for the location parameter. This unexpected result may be due to the internal and modeling uncertainties in the WRF model. The shape parameter was negative, meaning that there is an upper bound for extreme temperatures in the model.

Solar Rotation Effects in Earth's and Mars' Thermospheric Densities as Revealed by Concurrent MAVEN, Swarm‐C, and GOES Observations

AbstractThe responses of Earth's and Mars' thermospheric densities to quasi‐periodic (∼27‐day) solar rotation variations in flux were measured contemporaneously by the Mars Atmosphere and Volatile EvolutioN, Geostationary Operational Environmental Satellites, and Swarm‐C satellites. While large solar rotation variability is found in both planetary thermospheres, correlation analyses performed on over 6 years of observations reveal that, independently of extreme ultraviolet flux level, Earth's daytime density response is about 10%–50% larger than Mars' at a similar density level. Important altitude dependencies in the density sensitivity to the solar rotation in solar flux are found in the Martian thermosphere, while the terrestrial thermosphere is shown to exhibit only small (±5%) day/night and latitude variations in the response. Detailed analyses focused on correlative periods in 2015–2016 and 2020 indicate important solar cycle effects in the sensitivities of both planetary thermospheres, with increased slopes under low solar flux conditions. These results provide important new insights into processes relevant to the interpretation of the sources of short‐term density variability in Mars' and Earth's thermospheres associated with solar drivers and point to the need for targeted modeling efforts along with dedicated data analyses to help resolve current unknowns in thermal balance processes.

Assessment of the radiation risk at flight altitudes for an extreme solar particle storm of 774 AD

Intense solar activity can lead to an acceleration of solar energetic particles and accordingly increase in the complex radiation field at commercial aviation flight altitudes. We considered here the strongest ever reported event, namely that of 774 AD registered on the basis of cosmogenic-isotope measurements, and computed the ambient dose at aviation altitude(s). Since the spectrum of solar protons during the 774 AD event cannot be directly obtained, as a first step, we derived the spectra of the solar protons during the ground level enhancement (GLE) #5 on 23 February 1956, the strongest event observed by direct measurements, which was subsequently scaled to the size of the 774 AD event and eventually used as input to the corresponding radiation model. The GLE #5 was considered a conservative approach because it revealed the hardest-ever derived energy spectrum. The global map of the ambient dose was computed under realistic data-based reconstruction of the geomagnetic field during the 774 AD epoch, based on paleomagnetic measurements. A realistic approach on the basis of a GLE #45 on 24 October 1989 was also considered, that is by scaling an event with softer spectra and lower particle fluxes compared to the GLE #5. The altitude dependence of the event-integrated dose at altitudes from 30 kft to 50 kft (9.1–15.2 km) was also computed for both scenarios. Our study of the radiation effects during the extreme event of 774 AD gives the necessary basis to be used as a reference to assess the worst-case scenario for a specific threat, that is radiation dose at flight altitudes.

Impacts of Omicron associated restrictions on vertical distributions of air pollution at a suburb site in Shanghai

To prevent the Omicron transmission, Shanghai government implemented varying degrees of restraint measures. This study provided a new insight into the responses of air pollution altitude dependence to restraint measures by conducting vertical observations at a suburb site in Shanghai. Based on the difference-in-differences (DiD) models that compare the results in 2021 (normal scenario) and 2022 (Omicron-based restriction), we evaluated the casual effects of restrictions on (i) nitrogen dioxide (NO2), (ii) aerosol (presented by aerosol extinction coefficient (AEC)), formaldehyde (HCHO) and glyoxal (CHOCHO) and (iii) ozone (O3), which are generally treaded as primary, multi-sources and secondary pollutants, respectively. The estimated results from 0.0 to 2.0 km show that the drop/rise induced by restrictions is greater below 1.0 km than that above 1.0 km. Averaged on vertical distributions, AEC, NO2, HCHO and CHOCHO during restrictions felled by 15.1% (0.12 km−1), 40.3% (1.65 ppbv), 10.0% (0.26 ppbv) and 28.6% (21.79 pptv), respectively, while O3 increased by 21.3% (18.12 μg/m3). It indicates that restrictions induce significant drops in primary pollutants and enhancements in secondary pollutants. For multi-sources pollutants, the decline from primary sources can be partly offset by enhanced secondary productions, and the ratio of increased secondary sources to decreased primary sources can be elevated with height. The discrepancies of responses to restrictions are reflected in vertical distribution and types of air pollution, emphasizing the significance of vertical observations for diversified pollution. These finding can also be meaningful in the strategy development for prevention and control of air pollution.

Characterizing basin-scale precipitation gradients in the Third Pole region using a high-resolution atmospheric simulation-based dataset

Abstract. Altitudinal precipitation gradient plays an important role in the interpolation of precipitation in the Third Pole (TP) region, where the topography is very complex but in situ data are very sparse. This study proves that the altitude dependence of precipitation in the TP can be reasonably reproduced by a high-resolution atmospheric simulation-based dataset called ERA5_CNN. The precipitation gradients, including both absolute (APGs) and relative gradients (RPGs), for 388 sub-basins of the TP above 2500 m a.s.l. are calculated based on the ERA5_CNN. Results show that most sub-basins have positive precipitation gradients, and negative gradients are mainly found along the Himalayas, the Hengduan Mountains and the western Kunlun. The annual APG and RPG averaged across all sub-basins of the TP are 0.05 mm d−1 × 100 m−1 and 4.25 % × 100 m−1, respectively. The values of the APG are large in wet seasons but small in dry seasons, while the RPG shows opposite variations. Further analyses demonstrate that the RPGs have negative correlations with relative humidity but positive correlations with wind speed, likely because dry air tends to reach saturation at high altitudes, while stronger wind can bring more humid air to high altitudes. In addition, we find that precipitation gradients tend to be positive at small spatial scales compared to those at large scales, mainly because local topography plays a vital role in determining precipitation distribution at small scales. These findings on the spatiotemporal variations of precipitation gradients provide useful information for interpolating precipitation in the TP region.

Rate of atmospheric brown carbon whitening governed by environmental conditions

Biomass burning organic aerosol (BBOA) in the atmosphere contains many compounds that absorb solar radiation, called brown carbon (BrC). While BBOA is in the atmosphere, BrC can undergo reactions with oxidants such as ozone which decrease absorbance, or whiten. The effect of temperature and relative humidity (RH) on whitening has not been well constrained, leading to uncertainties when predicting the direct radiative effect of BrC on climate. Using an aerosol flow-tube reactor, we show that the whitening of BBOA by oxidation with ozone is strongly dependent on RH and temperature. Using a poke-flow technique, we show that the viscosity of BBOA also depends strongly on these conditions. The measured whitening rate of BrC is described well with the viscosity data, assuming that the whitening is due to oxidation occurring in the bulk of the BBOA, within a thin shell beneath the surface. Using our combined datasets, we developed a kinetic model of this whitening process, and we show that the lifetime of BrC is 1 d or less below ∼1 km in altitude in the atmosphere but is often much longer than 1 d above this altitude. Including this altitude dependence of the whitening rate in a chemical transport model causes a large change in the predicted warming effect of BBOA on climate. Overall, the results illustrate that RH and temperature need to be considered to understand the role of BBOA in the atmosphere.

The Local Time and Altitude Dependences of Long‐Lived Nonspecular Meteor Echoes With Weak Magnetic Aspect Sensitivity at Low Latitudes

AbstractLong‐lived nonspecular meteor echoes backscattered from meteor trail nonfield‐aligned irregularities (NFAIs) were observed sporadically at high latitudes. In this study, we employ the observations by the all‐sky radar of Meteor and ionospheric Irregularity Observation System (MIOS) at Ledong (18.4°N, 109°E) in October 2018, January, April, and July 2019, to investigate the occurrences of meteor trail NFAIs at low latitudes. A deep learning method was developed to identify long‐lived meteor echo events with durations of more than 5 s. The long‐lived echo events with triangular shape (a typical feature of nonspecular echo) in radar range‐time intensity maps were manually distinguished from those with nontriangular shape. Based on the cutoff magnetic aspect angle 12° of nonspecular meteor echoes from field‐aligned irregularities (FAIs), the local time and altitude dependences of meteor NFAIs producing long‐lived nonspecular echoes are investigated. A total of 846 meteor events due to the backscatters of NFAIs were observed. These events peak around the morning hours, with the beginning (end) altitudes up to (down to) 120 km (∼80 km). Their mean heights are about 2–6 km higher than specular meteor echoes. The occurrence of NFAI echoes peaks on certain days that is likely associated with meteor showers. The ratio of the observed NFAI echo to specular echo events is, on average, less than 1‰. Possible factors responsible for the NFAIs at low latitudes are discussed based on the current understanding of meteor dust trail.

Regional and Seasonal Dependence of the Potential Contrail Cover and the Potential Contrail Cirrus Cover over Europe

Ambient weather conditions strongly impact contrail formation and persistence. The implementation of contrail avoidance and mitigation strategies, therefore, requires regional and altitude-dependent information on the frequency of contrail occurrence. To this end, we have developed a method to quantify the potential contrail cover based on 10 years of high-resolution reanalysis of climatology and weather data from the European Center for Medium-Range Weather Forecast (ECMWF). We use the Schmidt–Appleman threshold temperature for contrail formation and additionally select thresholds for the relative humidity to evaluate the occurrence of persistent contrails and assess their regional and seasonal variation. We find a potential contrail cirrus cover of 10% to 20% above Europe at higher altitudes of 200 and 250 hPa in the 10-year climatology and a weak seasonal variation. At lower altitudes, near 300 hPa, a steep onset and a high potential contrail cirrus cover of 20% is found in late fall and in winter, decreasing to 2% potential contrail cirrus cover in summer. In comparison to ECMWF data, evaluations using data from the National Centers for Environmental Prediction (NCEP) show a significantly lower potential contrail cirrus cover. Our results help to investigate the seasonal and altitude dependence of contrail mitigation strategies, in particular for warming nighttime contrails that contribute strongly to the total climate impact from aviation.

MODELING THE SPATIAL RESOLUTION AND FLIGHT ALTITUDE DEPENDENCE OF THE RESPONSE IN RADIOMETRIC MONITORING USING UAV.

The result interpretation of a terrain airborne radiometric monitoring depends, among others, on the spatial resolution of the measurement (i.e. the area from which the value of the measured quantity is averaged) and on the altitude dependence of the response of the measuring device. For the needs of monitoring using unmanned aerial vehicles, the approximate values of these parameters were determined by stochastic calculations for selected model conditions. Calculations were of natural background components (K, U and Th) and the surface contamination with radionuclides emitting energies was in the range of 0.3-3MeV. The dependence on the source radius was modeled in the range of 2-450 m and flight altitude dependence was modeled in the range of 1-30 m. The modeled dependencies are used to refine the interpretation of experimental data, or to optimize the planning of monitoring the flight routes, according to specified monitoring objectives.