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Despite the growing number of GNSS sites, GNSS meteorology still suffers from insufficient observational data. This deficiency is particularly evident in GNSS tomography processing in the lowermost part of the troposphere, where the highest variability of weather conditions is observed. To address this challenge, we propose an integrated tomography solution that uses both ground-based GNSS observations and radio occultation (RO) excess phase in the same tomography model. Our integrated approach benefits from improved geometry and increased number of observations. In order to verify presented methodology, we use 41 GNSS stations and 78 RO profiles gathered during four different high precipitation events over the region of southern Poland. The results are validated against radiosonde observations and WRF reanalysis. Our study indicates an enhancement in the representation of wet refractivity on the order of 20 to 30% RMSE decrease when RO are integrated into the tomography solution with the mean error of final integrated product equal 3.5 ppm. [ABSTRACT FROM AUTHOR]

In this study, the multi-year data of meteorology and O3 from remote sensing and ground observations are applied to characterize the 3-D changes of O3 in the troposphere over central and eastern China (CEC) induced by the tropical cyclones (TCs) in the tropical and subtropical ocean regions over Northwest Pacific. The CEC-regional average of near-surface O3 levels is significantly elevated with 6.0 ppb in the large coverage by the TCs in the subtropical ocean, while the TCs in the tropical ocean alter near-surface O3 weakly, indicating the latitudinal-located TCs in the subtropical offshore ocean could largely influence the O3 variations over CEC. The sub-seasonal change with the positive and negative anomalies of near-surface O3 is induced by the tropical TCs from June to July and from August to October. The peripheral circulation of TCs in the subtropical offshore ocean persistently enhances the O3 concentrations over CEC during the season of East Asian summer monsoons. The positive O3 anomalies maintain from the entire troposphere to the lower stratosphere over CEC in the peripheries of subtropical TCs, while the tropical TCs cause the positive O3 anomalies merely in the lower troposphere. The O3 transport and accumulation, photochemical production and stratospheric intrusion are climatologically confirmed as the major meteorological mechanisms of TCs affecting the O3 variations. This study reveals that the downward transport of stratospheric O3 of TCs in the subtropical ocean exerts a large impact on the atmospheric environment over CEC, while the regional O3 transport and photochemical productions dominate the lower troposphere over CEC with less impact of stratospheric intrusion from the TCs in the tropical ocean region. These results present the climatology of tropospheric O3 anomalies in China induced by the TCs over the Northwest Pacific with enhancing our comprehension of the meteorological impact on O3 variations over the East Asian monsoon region. [ABSTRACT FROM AUTHOR]

A brief overview of the work of Russian scientists in the field of atmospheric chemistry in 20190–2022 is presented, including work on the chemistry of the troposphere, the chemistry of the ozone layer, the study of heterophase processes, and the chemical aspects of climate and its change. The review was prepared in the Commission on Atmospheric Chemistry of the Section of Meteorology and Atmospheric Sciences of the National Geophysical Committee. [ABSTRACT FROM AUTHOR]

This review outlines the most significant results of research in dynamic meteorology performed by Russian scientists in 2019–2022. It is part of the Russian National Report on Meteorology and Atmospheric Sciences submitted to the International Association of Meteorology and Atmospheric Sciences (IAMAS). The review is supplemented by a list of main publications of Russian scientists on dynamic meteorology in 2019–2022. [ABSTRACT FROM AUTHOR]

The generation of acoustic-gravity waves by meteorological heat sources in the troposphere and the propagation of these waves to the heights of the upper atmosphere are studied theoretically. Equations that describe separately the generation and propagation of acoustic and gravity waves by a local heat source are derived. The heat source of the waves is divided into partial sources of gravity and acoustic waves (AWs). The power of these partial sources is estimated and it is shown that the power of the sources differs by about a factor of two, regardless of the shape, size, and frequency of the heat source. It is shown that in the case of heat sources of the waves, the generation of gravity waves cannot occur without the corresponding generation of AWs: these waves are generated only in pairs. The splitting of the problem of waves from a heat source into problems of waves from gravity and acoustic sources is illustrated by the direct modeling of these waves. The application of the obtained results to the problem of parametrization of acoustic-gravity waves in general circulation and climate models is discussed. [ABSTRACT FROM AUTHOR]

Using state-of-the-art satellite ozone profile products, and chemical transport model, we provide an updated estimate of the tropospheric ozone radiative effect (TO3RE) and observational constraint on its variability over the decade 2008–2017. Previous studies have shown the short-term (i.e. a few years) globally weighted average TO3RE to be 1.17±0.03 W/m2, while our analysis suggests that the long-term (2008–2017) average TO3RE to be 1.21–1.28 W/m2. Over this decade, the modelled/observational TO3RE linear trends show negligible change (i.e. ±0.1 %/year), so the tropospheric ozone radiative contribution to climate has remained stable with time. Two model sensitivity experiments fixing emissions and meteorology to one year (i.e. start year – 2008) show that ozone precursor emissions (meteorological factors) have had limited (substantial) impacts on the long-term tendency of globally weighted average TO3RE. Here, the meteorological variability in the tropical/sub-tropical upper troposphere is dampening any tendency in TO3RE from other factors (e.g. emissions, atmospheric chemistry). [ABSTRACT FROM AUTHOR]

The idea that a tropospheric heat source generating waves can be replaced with a surface source of pressure oscillations on the Earth's surface is proposed and analyzed. In the surface source, atmospheric pressure fluctuations caused by a tropospheric source are used. The discrepancies due to the replacement of the tropospheric heat source by the surface one are estimated using experiments with a high-resilution numerical model of acoustic-gravity waves. It is shown that at frequencies of infrasound, the wave amplitudes in the upper atmosphere are very close for both tropospheric heat and surface pressure sources. At frequencies of internal gravity waves, the time-spatial structure of the wave fields are close in the upper atmosphere, but wave amplitudes for the surface pressure generation could be larger (up to two times) than those for the respective tropospheric heat sources. This discrepancy is explained and some corrections to the surface pressure source are proposed, which provide better agreement and may be applied for modeling of waves from tropospheric sources, based on the data of atmospheric microbarometer measurements. [ABSTRACT FROM AUTHOR]

In the fields of space geodetic techniques, such as Global Navigation Satellite System (GNSS), tropospheric zenith hydrostatic delay (ZHD) is chosen as the a priori value of tropospheric total delay. Therefore, the inaccuracy of ZHD will definitely infect parameters like the wet delay and the horizontal gradient of tropospheric delay, accompanied by an indirect influence on the accuracy of geodetic parameters, if not dealt with well at low elevation angles. In fact, however, the most widely used ZHD model currently seems to contain millimetre-level biases from the precise integral method. We explored the bias of traditional ZHD models and analysed the characteristics in different aspects on a global annual scale. It was found that biases differ significantly with season and geographical location, and the difference between the maximum and minimum values exceed 30 mm, which should be fully considered in the field of high-precision measurement. Then, we constructed a global grid correction model, which is named ZHD_crct, based on the meteorological data of year 2020 from ECMWF (European Centre for Medium-Range Weather Forecasts), and it turned out that the bias of traditional model in the current year could be reduced by ~50 % when the ZHD_crct was added. When we verified the effect of ZHD_crct on the biases in the next year, it worked almost the same as the former year. The mean absolute biases (MABs) of ZHD will be narrowed within ~0.5 mm for most regions, and the STD (standard deviation) will be within ~0.7 mm. This improvement will be helpful for researches on meteorological phenomena as well. [ABSTRACT FROM AUTHOR]

The generation and propagation of waves from model tropospheric meteorologic heat sources are theoretically studied. The processes of gas heating/cooling in water phase transitions at tropospheric altitudes are assumed to be the wave sources. In an analytical part of the study, equations are derived which describe the generation and propagation of acoustic and internal gravity waves separately. It is shown that powers of partial sources of acoustic and internal gravity waves always approximately coincide, regardless of wave frequencies, and the generation of internal gravity waves cannot occur without the generation of acoustic waves, and vice versa. Explicit analytical expressions are obtained for the generated waves. Due to resonant properties of the atmosphere, the high-frequency sources generate predominantly acoustic waves. The low-frequency sources generate mainly internal gravity waves if the sources work long enough for the resonance properties of atmosphere to be manifested. Using numerical experiments, the issue of error is investigated which is introduced if a tropospheric source is replaced with a surface one in which the pressure fluctuations on the surface are the recorded pressure fluctuations caused by the tropospheric source. It is shown that, if a tropospheric source operates at the infrasonic wave frequencies, then the wave patterns generated in the upper atmosphere from the tropospheric source and from the surface pressure fluctuations are almost identical. In the case of a tropospheric source operating at frequencies of internal gravity waves, the amplitude of waves from the surface pressure may be overestimated no more than twice. It is shown that, based on pressure fluctuations on the Earth's surface, some corrected surface pressure source can be constructed which takes into account the phase shifts of interfering waves that propagate into the upper atmosphere. This provides a significant improvement in the simulation of waves from meteorological sources based on data on atmospheric pressure fluctuations. [ABSTRACT FROM AUTHOR]

By using the multi-source data of meteorology over recent decades, this study discovered a summertime "hollow wet pool" in the troposphere with a center of high water vapor over the Asian water tower (AWT) on the Tibetan Plateau (TP), which is indicated by a vertical transport "window" in the troposphere. The water vapor transport in the upper troposphere extends from the vertical transport window over the TP with significant connections among the Arctic, Antarctic and TP regions, highlighting the effect of the TP's vertical transport window of water vapor in the troposphere on global change in water vapor. The vertical transport window is built by the AWT's thermal forcing in association with the dynamic effect of the TP's "hollow heat island". Our study improves the understanding of the vapor transport over the TP with important implication for global climate change. [ABSTRACT FROM AUTHOR]

Atmospheric refractivity fields are more strongly affected by more water vapor in the tropical lower troposphere than elsewhere. In this study, based on model simulations, we first collocated the radio occultation (RO) data in 2009 from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) with CloudSat cloud profiling radar data. We then investigate where and why a RO ray path intersects with other simulated rays of impact heights above and/or below the impact height of the ray. Using the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis as input to a raytracing observation operator, we show that the simulated impact parameters could vary along the ray in the tropical lower troposphere. For brevity, an intersection of a GPS RO ray path with rays above it or below it or both will be called an impact multipath. By overlapping simulated ray trajectories over the vertical and horizontal gradients of refractivity in 2D occultation planes, impact multipath occurrences are vividly illustrated. Statistical results show that the impact multipath is caused mostly by strong local vertical gradients of atmospheric wet refractivity mostly within 300 km horizontal distances from their perigee positions. The impact multipath occurs more frequently below 5-km impact height, with a maximum occurrence around the 3.4 km impact height (about 1.8 km geometric height). It is shown that both the simulated impact multipath phenomena and locally strong vertical gradients of wet refractivity are found in both cloudy and clear-sky conditions, and most frequently in presences of stratocumulus clouds. [ABSTRACT FROM AUTHOR]

Remote sensing of water vapor using Global Navigation Satellite Systems (GNSS) is a well-established tool for weather and climate monitoring. The current challenges of GNSS meteorology are real-time performance and the inclusion of emerging GNSS, such as Galileo. We demonstrate that real-time GPS-only, Galileo-only, and GPS+Galileo solutions are consistent among each other. However, our results show that the Galileo-only solutions tend to underestimate Zenith Total Delay (ZTD) with respect to GPS. The Galileo-only real-time ZTD is less accurate as the one from GPS. The combination of both GNSS leads to a superior product. The daily solution availability increases by up to 50%, and the overall gain is 0.7% over the entire year. The accuracy improves by 3.7% to 8.5% and uncertainty is reduced by a factor of 1.5–2. A combined GPS and Galileo solution suppresses artifacts in a real-time ZTD product which otherwise would be attributed to high-frequency orbital effects. [ABSTRACT FROM AUTHOR]

This review outlines the most important results of research in dynamic meteorology performed by Russian scientists in 2015–2018. It is part of the Russian National Report on Meteorology and Atmospheric Sciences submitted to the International Associations of Meteorology and Atmospheric Sciences (IAMAS). A list of major published papers on dynamic meteorology over 2015–2018 is attached. [ABSTRACT FROM AUTHOR]

This is a brief review of Russian studies in the field of atmospheric chemistry for 2015–2018, covering studies on tropospheric chemistry, chemistry of the ozone layer, heterophase processes, and those related to the chemical aspects of climate and its changes. The review was prepared by the Commission for Atmospheric Chemistry of the Meteorology and Atmospheric Sciences Section of the National Geophysical Committee. The report was considered and approved at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG)1. [ABSTRACT FROM AUTHOR]

East Asian dust has a significant impact on regional and global climate. In this study, we evaluate the spatial distributions and temporal variations of dust extinction profiles and dust optical depth (DOD) over East Asia simulated from the Community Earth System Model (CESM) with satellite retrievals from Luo, Wang, Ferrare, et al. (2015, https://doi.org/10.1029/2002JD002775), Luo, Wang, Zhang, et al. (2015, https://doi.org/10.1002/2014GL062111) (L15), Yu et al. (2015, https://doi.org/10.1016/j.rse.2014.12.010) (Y15), and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) level 3 products. Both L15 and Y15 are based on CALIPSO products but use different algorithms to separate dust from nondust aerosols. We find high model biases of dust extinction in the upper troposphere over the Taklamakan desert, Gobi desert, and Tibetan Plateau, especially in the summer (June‐July‐August). CESM with dust emission scheme of Kok, Mahowald, et al. (2014, https://doi.org/10.5194/acp‐14‐13023‐2014) and Kok, Albani, et al. (2014, https://doi.org/10.5194/acp‐14‐13043‐2014) has the best agreement with dust extinction profiles and DOD from L15 in the Taklamakan desert and Tibetan Plateau. CESM with the default dust emission scheme of Zender, Bian, and Newman (2003, https://doi.org/10.1029/2002JD002775) underpredicts DOD in the Tibetan Plateau compared with observations from L15 due to the underestimation of local dust emission. Large uncertainties exist in observations from L15, Y15, and CALIPSO level 3 products and have significant impacts on the model evaluation of dust spatial distributions. We also assess dust surface concentrations and 10‐m wind speed with meteorological records from weather stations in the Taklamakan and Gobi deserts during dust events. CESM underestimates dust surface concentrations at most weather stations due to the inability of CESM to capture strong surface wind events. Key Points: CESM with K14 dust emission scheme has the best agreement with dust extinction profiles and DOD from CALIPSO in East AsiaLarge uncertainties exist in observations from CALIPSO and have significant impacts on the model evaluation of dust spatial distributionsCESM underestimates dust surface concentrations in East Asia due to the its inability to capture strong surface wind events [ABSTRACT FROM AUTHOR]

Highlights • Topography weakens orbital forcing of climate at high latitudes. • Topographically forced circulation exhibits a hemispheric asymmetry • Precipitation minus evaporation always peaks near the north pole. • Titan's asymmetric lake distribution may resist the Croll–Milankovitch cycle. Abstract Previously, seasonal asymmetry in Titan's climate caused by Saturn's orbital eccentricity was proposed as a possible external cause of the asymmetric polar lake distribution on Titan. However, climate studies of other planets indicate that seasonal asymmetry can also be caused by a hemispheric asymmetry in geography such as the ocean-continent distribution or topography. A global climate model is used to investigate whether orbital forcing or hemispheric asymmetry in geography is more important for the seasonal asymmetry in Titan's climate and the distribution of polar methane deposits. Titan's large-scale topography generally decreases from equator to pole and thereby induces meridional circulation with upwelling at low latitudes and downwelling at high latitudes due to near-surface horizontal temperature gradients. This circulation is stronger in the southern hemisphere, which contains steep slopes at mid latitudes, and acts to transport dry air downward near the south pole and to reduce the precipitation in southern summer. Consequently, the annual precipitation minus evaporation is substantially smaller in the south polar region than in the north polar region. Orbital parameter variations quantitatively affect the polar precipitation, yet are unable to reverse the vast hemispheric asymmetry in the polar precipitation. The accumulation of Titan's lakes near the north pole could therefore be a semi-permanent feature related to Titan's topography and may resist the Croll–Milankovitch cycle. [ABSTRACT FROM AUTHOR]

Ultrafine particles (UFPs) are distributed highly unevenly in the lower troposphere. Although these UFPs are positively detectable and have been studied for more than a century, their three-dimensional distribution, formation, and budget in the atmosphere remain largely uncertain, despite their obvious climate relevance. This is due to their short lifetime and the fact that they are invisible to the human eye and to remote sensing techniques. From the moment of their emission or generation, their spatial distribution is a result of meteorological processes, regional-scale transport, local thermal convection, and rapid loss by interaction with clouds as cloud condensation nuclei. Here, we report about three-dimensional airborne in situ studies aimed at investigating UFP sources, distribution, and behavior on different spatial and temporal scales. We identified fossil fuel–burning power stations, refineries, and smelters as major anthropogenic UFP sources. On a regional scale, their emissions are significantly higher than urban emissions. Particle emissions from such power stations are released typically at altitudes between 200 and 300 m AGL. Detailed in situ measurements of particle concentration and related parameters, together with meteorological measurements and analyses, enable reliable source attribution even over several hundred kilometers downwind from the emitter. Comprehensive meteorological analysis is required to understand the highly variable 3D concentration patterns generated by advective transport and thermal convection. Knowledge of primary emission strength, together with size distributions and atmospheric 3D transport of UFPs derived from airborne measurements, makes it possible to estimate the aerosols' impact on meteorology, hydrological cycles, and climate. [ABSTRACT FROM AUTHOR]

Troposphere plays crucial role for geodetic comunity, which can primarly be seen in its influence on GNSS observations. At the same time, troposhpere is the place where almost all hidrometeorological phenomena that effect our everyday life occure. Scientists have found a way to use systematic influence that troposphere has on GNSS signal and turn it into meteorological indicator, water vapor quantity. In this paper term of GNSS meteorology is described, as well as its basic classification and application.

The cities of Chengdu, Deyang, and Mianyang in the northwest Sichuan Basin are part of a rapidly developing urban agglomeration adjoining the eastern slopes of the Tibetan Plateau. Heavy air pollution events have frequently occurred over these cities in recent decades, but the effects of meteorological conditions on these pollution events are unclear. We explored the effects of weather systems on winter heavy air pollution from 1 January 2006 to 31 December 2012 and from 1 January 2014 to 28 February 2017. A total of 10 heavy air pollution events occurred during the research period and 8 of these took place while the region was affected by a dry low-pressure system at 700 hPa. When the urban agglomeration was in front of the low-pressure system and the weather conditions were controlled by a warm southerly air flow, a strong temperature inversion appeared above the atmospheric boundary layer acting as a lid. Forced by this strong inversion layer, the local secondary circulation was confined to the atmospheric boundary layer, and the horizontal wind speed in the lower troposphere was low. As a result, vertical mixing and horizontal dispersion in the atmosphere were poor, favoring the formation of heavy air pollution events. After the low-pressure system had transited over the region, the weather conditions in the urban agglomeration were controlled by a dry and cold air flow from the northwest at 700 hPa. The strong inversion layer gradually dissipated, the secondary circulation enhanced and uplifted, and the horizontal wind speed in the lower troposphere also increased, resulting in a sharp decrease in the concentration of air pollutants. The strong inversion layer above the atmospheric boundary layer induced by the low-pressure system at 700 hPa thus played a key role in the formation of heavy air pollution during the winter months in this urban agglomeration. This study provides scientific insights for forecasting heavy air pollution in this region of China. [ABSTRACT FROM AUTHOR]

Abstract: Western disturbances (WDs) are midtropospheric to upper‐tropospheric mesoscale vortices, which typically propagate along the subtropical westerly jet stream and bring heavy rainfall to Pakistan and northern India during boreal winter. They are dynamically similar to Tibetan Plateau vortices (TPVs), which affect southwest China during spring and summer and emanate from the Tibetan Plateau. Here we propose that their similarity implies the existence of a more general group of upper‐tropospheric vortices featuring interactions with the orography of the Hindu Kush‐Himalaya‐Tibetan Plateau region. Using existing track databases for WDs and TPVs derived from ERA‐Interim reanalysis, we show that their respective occurrence frequencies are highly anticorrelated with each other through the seasonal cycle, yet both are strongly correlated with jet latitude. Our findings imply that the incidence of hazards due to WDs and TPVs is correlated on intra‐annual and interannual time scales, particularly through upper‐level baroclinicity. [ABSTRACT FROM AUTHOR]

Posterior fluxes obtained from inverse modelling are difficult to verify because there is no dense network of flux measurements available to evaluate estimates against. Here we present a new diagnostic to evaluate structures in posterior fluxes. First, we simulate the change in atmospheric CO2 fields between posterior and prior fluxes, referred to as the posterior atmospheric adjustments due to updated fluxes (PAAFs). Second, we calculate the uncertainty in atmospheric CO2 fields due solely to uncertainty in the meteorological fields, referred to as the posterior atmospheric adjustments due to imperfect meteorology (PAAMs). We argue that PAAF can only be considered robust if it exceeds PAAM, that is, the changes in atmospheric CO2 between the posterior and prior fluxes should at least exceed atmospheric CO2 changes arising from imperfect meteorology. This diagnostic is applied to two CO2 flux inversions: one which assimilates observations from the in situ CO2 network and the other which assimilates observations from the Greenhouse Gases Observing SATellite (GOSAT). On the global scale, PAAF in the troposphere reflects northern extratropical fluxes, whereas stratospheric adjustments primarily reflect tropical fluxes. In general, larger spatiotemporal variations in PAAF are obtained for the GOSAT inversion than for the in situ inversion. Zonal standard deviations of the PAAF exceed the PAAM through most of the year when GOSAT observations are used, but the minimum value is exceeded only in boreal summer when in situ observations are used. Zonal spatial structures in GOSAT-based PAAF exceed PAAM throughout the year in the tropics and through most of the year in the northern extratropics, suggesting GOSAT flux inversions can constrain zonal asymmetries in fluxes. However, we cannot discount the possibility that these structures are influenced by biases in GOSAT retrievals. Verification of such spatial structures will require a dense network of independent observations. Because PAAF depends on the choice of prior fluxes, the comparison with PAAM is system dependent and thus can be used to monitor a given assimilation system's behaviour. [ABSTRACT FROM AUTHOR]

An error in calculating the tropospheric delay of satellite navigation signals is estimated for different atmospheric phenomena. As atmospheric phenomena, different precipitation types (hydrometeors) and electrical phenomena (thunderstorms and summer lightning) are considered. The tropospheric delay is calculated for the Saastamoinen and Hopfield models with the vertical profiles of the atmospheric meteorological parameters obtained by aerological sounding. The error of the given methods is determined by a comparison of the calculated and true values of the zenith tropospheric delays. The influence of the atmospheric phenomena on the error value is analyzed. [ABSTRACT FROM AUTHOR]

This work presents the results of a Conventional Empirical Orthogonal Function Analysis on daily global zonal mean temperature profiles in the Upper Troposphere and Lower Stratosphere (15–35 km), as measured by the FORMOSAT-3/COSMIC mission from January 2007 to June 2013. For validation, results were compared with ERA-Interim reanalysis. Results show that, the leading global EOF mode (27%) from COSMIC is consistent with temperature anomalies due to the tropical cooling associated with boreal winter Sudden Stratospheric Warmings (SSW). The second global EOF mode from COSMIC (15.3%) is consistent with temperature anomalies due to the Quasi-biennial Oscillation (QBO). The third global mode from COSMIC (10.9%) is consistent with temperature anomalies due to the El Nino Southern Oscillation. This work also shows that the second northern hemisphere EOF mode from COSMIC (16.8%) is consistent with temperature anomalies due Rossby-wave breaking (RWB) which is expected to only be resolved by a high vertical and temporal resolution dataset like COSMIC. Our work concludes that the use of a high vertical and temporal resolution dataset like COSMIC yields non-seasonal EOF modes that are consistent with relatively more intricate temperature anomalies due to the SSW, QBO, ENSO and RWB. [ABSTRACT FROM AUTHOR]

Radio refractivity plays a significant role in the development and design of radio systems for attaining the best level of performance. Refractivity in the troposphere is one of the features affecting electromagnetic waves, and hence the communication system interrupts. In this work, a modified artificial neural network (ANN) based model is applied to predict the refractivity. The suggested ANN model comprises three modules: the data preparation module, the feature selection module, and the forecast module. The first module applies pre-processing to make the data compatible for the feature selection module. The second module discards irrelevant and redundant data from the input set. The third module uses ANN for prediction. The ANN model applies a sigmoid activation function and a multi-variate auto regressive model to update the weights during the training process. In this work, the refractivity is predicted and estimated based on ten years (2002–2011) of meteorological data, such as the temperature, pressure, and humidity, obtained from the Pakistan Meteorological Department (PMD), Islamabad. The refractivity is estimated using the method suggested by the International Telecommunication Union (ITU). The refractivity is predicted for the year 2012 using the database of the previous ten years, with the help of ANN. The ANN model is implemented in MATLAB. Next, the estimated and predicted refractivity levels are validated against each other. The predicted and actual values (PMD data) of the atmospheric parameters agree with each other well, and demonstrate the accuracy of the proposed ANN method. It was further found that all parameters have a strong relationship with refractivity, in particular the temperature and humidity. The refractivity values are higher during the rainy season owing to a strong association with the relative humidity. Therefore, it is important to properly cater the signal communication system during hot and humid weather. Based on the results, the proposed ANN method can be used to develop a refractivity database, which is highly important in a radio communication system. [ABSTRACT FROM AUTHOR]

Aside from the well-known applications (positioning, navigation and timing) brought by Global Navigation Satellite System (GNSS), reconstruction of tropospheric atmosphere distribution information using tomography technique based on the multi-GNSS observations has been developed as a research point in the fields of GNSS Meteorology. In this paper, an optimal tropospheric tomography method using observations from multi-GNSS (Global Navigation Satellite System) is proposed, which considers the reasonable weightings of observation equations derived from multi-GNSS as well as the various constraints. Comparing to the equal weighting strategy of multi-GNSS observations for the previously multi-GNSS tomography studies, the proposed method in this paper has the ability to tune the weightings for a different type of equations. Experiments show that the proposed method can improve the internal/external accuracy of GNSS tomography modeling with the GNSS precise point positioning (PPP)-estimated slant wet delay as reference when compared to the conventional method. In addition, the data derived from radiosonde is used as an external testing, and the result also expresses the superiority of the proposed method when compared to the conventional method. [ABSTRACT FROM AUTHOR]

The multi-constellation Global Navigation Satellite Systems (GNSS) offers promising potential for the retrieval of real-time (RT) atmospheric parameters to support time-critical meteorological applications, such as nowcasting or regional short-term forecasts. In this study, we processed GNSS data from the globally distributed Multi-GNSS Experiment (MGEX) network of about 30 ground stations by using the precise point positioning (PPP) technique for retrieving RT multi-GNSS tropospheric delays. RT satellite orbit and clock product streams from the International GNSS Service (IGS) were used. Meanwhile, we assessed the quality of clock and orbit products provided by different IGS RT services, called CLK01, CLK81, CLK92, GFZC2, and GFZD2, respectively. Using the RT orbit and clock products, the performances of the RT zenith total delays (ZTD) retrieved from single-system as well as from multi-GNSS combined observations were evaluated by comparing with the U.S. Naval Observatory (USNO) final troposphere products. With the addition of multi-GNSS observations, RT ZTD estimates with higher accuracy and enhanced reliability compared to the single-system solution can be obtained. Compared with the Global Positioning System (GPS)-only solution, the improvements in the initialization time of ZTD estimates are about 5.8% and 8.1% with the dual-system and the four-system combinations, respectively. The RT ZTD estimates retrieved with the GFZC2 products outperform those derived from the other IGS-RT products. In the GFZC2 solution, the accuracy of about 5.05 mm for the RT estimated ZTD can be achieved with fixing station coordinates. The results also confirm that the accuracy improvement (about 22.2%) can be achieved for the real-time estimated ZTDs by using multi-GNSS observables, compared to the GPS-only solution. In the multi-GNSS solution, the accuracy of real-time retrieved ZTDs can be improved by a factor of up to 2.7 in the fixing coordinate mode, compared with that in the kinematic mode. [ABSTRACT FROM AUTHOR]

We investigated the predictability of plume advection in the lower troposphere and the impact of AMeDAS surface wind data assimilation by using radioactive cesium emitted by the Fukushima nuclear accident in March 2011 as an atmospheric tracer. We conducted two experiments of radioactive plume predictions over eastern Japan for March 15, 2011 with a 3-km horizontal resolution using the Japan Meteorological Agency non-hydrostatic weather forecast model and local ensemble transform Kalman filter (JMANHM-LETKF) data assimilation system. The assimilated meteorological data were obtained from the standard archives collected for the Japan Meteorological Agency operational numerical weather prediction and the AMeDAS surface wind observations. The standard archives do not contain land-surface wind observations. The modeled radioactive cesium concentrations were examined for plume arrival times at 40 observatories. The mean error of the plume arrival times for the standard experiment (assimilating only the standard archives) was 82.0 min with a 13-h lead-time on an average. In contrast, the mean error of the AMeDAS experiment (assimilating both the standard archives and AMeDAS surface wind observations) was 72.8 min, which was 9.2 min (11 %) better than that of the standard experiment. This result indicates that the plume prediction has a reasonable accuracy for the environmental emergency response and the prediction can be significantly improved by the surface wind data assimilation. [ABSTRACT FROM AUTHOR]