Sounder Satellite Research Articles

The role of refractive indices in measuring mineral dust with high-spectral-resolution infrared satellite sounders: application to the Gobi Desert

Abstract. Mineral dust significantly influences the Earth's climate system by affecting the radiative balance through the emission, absorption and scattering of solar and terrestrial radiation. Estimating the dust radiative effect remains challenging due to the lack of detailed information on the physical and chemical properties of dust. High-spectral-resolution instruments in the infrared (IR) spectrum, such as the Infrared Atmospheric Sounding Instrument (IASI), have demonstrated the ability to quantify these aerosol properties. A crucial parameter for characterizing mineral dust from space is the complex refractive index (CRI), as it links the dust's physical and chemical properties to its optical properties. This paper examines the impact of six prior laboratory CRI datasets to improve the characterization of dust microphysical properties using IASI. The CRIs include older measurements obtained through the classical pellet method, commonly employed in mineral dust applications, as well as newer datasets that incorporate the latest advancements in laboratory measurement techniques for aerosol generation. These datasets are tested on IASI measurements during a dust storm event over the Gobi Desert in May 2017. We evaluate the sensitivity of IASI to different CRI datasets using the Atmospheric Radiation Algorithm for High-Spectral Resolution Measurements from Infrared Spectrometer (ARAHMIS) radiative transfer algorithm and explore the datasets' impact on retrieving size distribution parameters by mapping their spatial distributions. The results indicate that the laboratory CRI datasets decrease the total error in the covariance matrix by 30 %. In addition, we assess the ability to accurately reconstruct IASI detections and the extent to which we can retrieve the microphysical properties of dust particles. The choice of CRI significantly impacts the accuracy of dust detection and characterization from satellite observations. Notably, datasets that incorporate recent aerosol generation techniques with higher spectral resolution and samples from the case study region show improved compatibility with IASI observations. The outcomes of this research emphasize two key points: the crucial link between chemical composition of dust and its optical properties and the importance of considering the specific composition of the CRI dataset for improved retrieval of the microphysical parameters. Furthermore, this study highlights the critical role of ongoing enhancements in CRI measurement approaches, as well as the potential of high-spectral-resolution infrared sounders for aerosol atmospheric investigation and for understanding the radiative impacts of sounders.

Demonstration of a physical inversion scheme for all-sky, day-night IASI observations and application to the analysis of the onset of the Antarctica ozone hole: Assessment of retrievals and consistency of forward modeling

Based on a recently developed all-sky forward model (σ-IASI/F2N) for the computation of spectral radiances in the range 100 to 2760 cm-1, the paper addresses the spring onset of the Antarctica ozone hole with infrared observations from the IASI (Infrared Atmospheric Sounder Interferometer) satellite sounder. The Antarctica ozone hole is a cyclic event that grows in normal conditions in late August and collapses in late November/early December. Because of climate change (cooling of the stratosphere), the O3 hole is expected to become deeper. Indeed, 2021 and 2023 have been characterized by very spatially extensive and deep ozone hole. To demonstrate that we can gain further insights into these phenomena with the help of infrared nadir viewing observations, we have developed an all-sky retrieval tool, which inverts the whole IASI infrared spectrum to simultaneously estimate thermodynamic and geophysical parameters, including ozone and nitric acid, which are key parameters in analyzing the Antarctic ozone hole. Infrared sounders acquire data day and night, unlike visible and ultraviolet sounders, which are only operational during daytime. This enables us to acquire data also during the polar night, which is a critical time for O3 hole formation. Ice polar stratospheric clouds have been identified and fitted with our scheme. Maps of atmospheric ozone, complemented with those of nitric acid, temperature, and lower stratosphere height, have been retrieved for July, September, and October 2021 and 2023. Results are compared to those derived from TROPOMI (TROPOspheric Monitoring Instrument) and OMI (Ozone Monitoring Instrument), showing a very good agreement. The comparison of simultaneously retrieved O3 and HNO3 shows that the onset of the ozone hole is associated with relevant denitrification in the Antarctica Stratosphere. For 2023, our findings also show that O3 depletion episodes began as early as July. Although demonstrative, our analysis evidences the importance of Numerical Weather Prediction centers to assimilating all-sky infrared radiances (day, night, clear, or with ice or water clouds) to get insights into providing a more comprehensive picture of the Southern Spring ozone depletion over Antarctica.

Satellite and in situ measurements of water vapour in the Brazil‐Malvinas Confluence region

AbstractThis decade‐long study from the INTERCONF programme addresses the data gap on ocean dynamics in the Southern Hemisphere. Focusing on the Brazil‐Malvinas Confluence (BMC), we investigated the effect of temperature differences between the warm Brazil Current (BC) and the cold Malvinas Current (MC) on water vapour in the marine atmospheric boundary layer (MABL). Our results show a clear distinction: warmer BMC waters have 32% more water vapour (2 kg·m−2 on average) compared to the MC. This highlights the direct link between ocean temperatures and atmospheric processes. Analysis of radiosonde data alongside satellite measurements showed better agreement over cooler waters with lower water vapour, leading to lower variability. This suggests less atmospheric turbulence and improved data compatibility, especially for satellite retrievals such as AIRS. Comparisons between reanalysis data (CFSR), satellite sounders (AIRS) and radiosondes (RS) showed consistent air temperature profiles, with average errors within the 10% threshold for satellite measurements. While capturing humidity variations remains a challenge, especially at high concentrations (indicated by higher mean squared error values), our study highlights the reliability of satellite data, particularly over the cold BMC region. This research highlights the importance of studying the interactions between ocean fronts and atmospheric phenomena for a complete picture of Southern Hemisphere ocean dynamics. It offers valuable insights for scientists across disciplines, providing a broad perspective on the results and their significance in different contexts.

Combined assimilation of NOAA surface and MIPAS satellite observations to constrain the global budget of carbonyl sulfide

Abstract. Carbonyl sulfide (COS), a trace gas in our atmosphere that leads to the formation of aerosols in the stratosphere, is largely taken up by terrestrial ecosystems. Quantifying the biosphere uptake of COS could provide a useful quantity to estimate gross primary productivity (GPP). Some COS sources and sinks still contain large uncertainties, and several top-down estimates of the COS budget point to an underestimation of sources, especially in the tropics. We extended the inverse model TM5-4DVAR to assimilate Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite data, in addition to National Oceanic and Atmospheric Administration (NOAA) surface data as used in a previous study. To resolve possible discrepancies among the two observational data sets, a bias correction scheme is necessary and implemented. A set of inversions is presented that explores the influence of the different measurement streams and the settings of the prior fluxes. To evaluate the performance of the inverse system, the HIAPER Pole-to-Pole Observations (HIPPO) aircraft observations and NOAA airborne profiles are used. All inversions reduce the COS biosphere uptake from a prior value of 1053 GgS a−1 to much smaller values, depending on the inversion settings. These large adjustments of the biosphere uptake often turn parts of Amazonia into a COS source. Only inversions that exclusively use MIPAS observations, or strongly reduce the prior errors on the biosphere flux, maintain the Amazon as a COS sink. Inclusion of MIPAS data in the inversion leads to a better separation of land and ocean fluxes. Over the Amazon, these inversions reduce the biosphere uptake from roughly 300 to 100 GgS a−1, indicating a strongly overestimated prior uptake in this region. Although a recent study also reported reduced COS uptake over the Amazon, we emphasise that a careful construction of prior fluxes and their associated errors remains important. For instance, an inversion that gives large freedom to adjust the anthropogenic and ocean fluxes of CS2, an important COS precursor, also closes the budget satisfactorily with much smaller adjustments to the biosphere. We achieved better characterisation of biosphere prior and uncertainty, better characterisation of combined ocean and land fluxes, and better constraint of both by combining surface and satellite observations. We recommend more COS observations to characterise biosphere and ocean fluxes, especially over the data-poor tropics.

On the use of routine airborne observations for evaluation and monitoring of satellite observations of thermodynamic profiles

Abstract. Satellite-based observations require independent sources of data to monitor and evaluate their precision and accuracy. For the temperature and water vapor profiles produced by satellite-based sounders, this typically results in comparisons to operational radiosonde observations. However, polar-orbiting satellite overpasses are frequently misaligned with the global synoptic launch times. The routine airborne in situ observations of temperature and water vapor from the Airborne Meteorological Data Relay (AMDAR) program and the Water Vapor Sensing System-II (WVSS-II) instrument greatly enhance opportunities to make precise matchups due to the far greater temporal frequency and spatial density of aircraft flights. The potential for the use of aircraft-based observations as a source of evaluation of tropospheric satellite sounder profiles is explored through a year-long intercomparison with the Infrared Atmospheric Sounding Interferometer (IASI) level-2 profiles produced from both the Metop-A and Metop-B satellites. Results using 1 h and 50 km match criteria indicating good agreement between the satellites and the aircraft-based observations with temperature, specific humidity, and relative humidity biases generally less than 0.5 K, 0.8 g kg−1, and 5 %, respectively; both IASI instruments perform nearly identically. While the intercomparisons are generally limited to the troposphere as aircraft typically reach their maximum height at the tropopause, the substantially larger number of intercomparison points enable characterization as a function of season, scan angle, and other characteristics heretofore unexplored due to a lack of sufficient validation data.

A high-precision retrieval method for methane vertical profiles based on dual-band spectral data from the GOSAT satellite

Satellite remote sensing has become an important method of monitoring methane concentrations. The full-physics algorithm is widely used for methane vertical profile retrieval, but the method is relatively time-consuming. Most current studies have focused on the retrieval of methane vertical profiles from thermal infrared (TIR) spectral data only, resulting in low accuracy in the near-surface retrieval results. To obtain the atmospheric methane vertical profile from satellite sounding data quickly and accurately, this paper proposes a high-precision retrieval method based on the ResNet18 model, a conventional and effective deep convolutional neural network, using TIR band and shortwave infrared (SWIR) band spectral data from the GOSAT. The model performs well on the test set, with mean absolute error (MAE) below 12.78 ppb and root mean square error (RMSE) below 23.71 ppb with pressure greater than 150 hPa. The accuracy of the retrieval results and GOSAT CH4 vertical profile products are validated using airborne measurement data. In the mid-latitude region, using NOAA airborne measurement data as reference values, the average of MAE and RMSE of the retrieval results between 500 hPa and 900 hPa are reduced by 12.05 ppb and 14.07 ppb, respectively, compared to the GOSAT CH₄ vertical profile product. In the low-latitude region, using CARIBIC airborne measurement data as reference values, the average of MAE and RMSE between 300 hPa and 600 hPa are reduced by 11.18 ppb and 12.20 ppb, respectively. The validation results show that the methane vertical profile can be quickly and accurately retrieved based on the ResNet18 model, combined with dual-band spectral data, temperature, and surface pressure.

Validation of Version 1.3 Ozone Measured by the SOFIE Instrument

AbstractThe Solar Occultation for Ice Experiment (SOFIE) has operated aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite since 2007. SOFIE uses solar occultation to retrieve ozone (O3) profiles from ∼20 to 100 km altitude, typically at polar latitudes. This study validates SOFIE O3 profiles, including error analysis and comparisons with independent observations. Comparisons are made to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite instruments. SOFIE shows qualitative and quantitative agreement with both data sets between 30 and 70 km and better overall agreement in the northern hemisphere. SOFIE and ACE mean differences are typically within 20% in the 30–70 km altitude range. SOFIE and MIPAS exhibit mean difference values within 30% in the winter and 20% for all other seasons averaged, between ∼30 and 60 km. Seasonal comparisons indicate similar variations in both hemispheres and through all seasons. The comparisons indicate that SOFIE is biased 5%–10% low at 30–70 km altitudes, with greater differences at higher and lower altitudes. The comparisons are challenging due to the low O3 concentrations at high altitudes, the limited number of coincidences, and the large diurnal variation in mesospheric O3 during twilight hours.

State and Stability of Forest Ecosystems of the Region with Extreme Anthropogenic Transformation (Evidence from the Oka River Basin)

Using satellite sounding data on the forest cover of Russia and three GIS programs, mapping of forest cover and average crown density in the Oka river basin was carried out. Considering hydro-ecological role of forests, these parameters were differentiated according to water management areas. The progressive decline in the wooded areas, thinning and defoliation of forest stands confirm the validity of classifying the Oka river basin as a territory with a catastrophic environmental situation. This is especially true for the forest-steppe zone, where the forest cover ranges from 2.4 to 40%. The average canopy density of the forests in the basin is 50.7%, which makes a significant part of them approaching the state of sparse hemi-xerophytic forests. Using the methods developed by the authors, the indices of the resistance and elastic-plastic stability of forests were calculated and the corresponding maps for the Oka river basin were constructed. It was found that the replacement of primary mixed and broadleaf forests with secondary small-leaved forests leads to a general increase in the dynamism of forest communities: to an increase in their sensitivity to disturbing signals and to an acceleration of ecogenetic successional changes that tend to transfer them to their previous (or new) stable state. The ordination of forest formations of the Oka river basin was carried out according to the gradients of the indices of resistance and elastic-plastic stability. The overwhelming majority of forest formations are characterized by high sensitivity to the initial signals of external disturbances, but at the same time, by sufficiently developed mechanisms of ecogenetic successions, which represent their elastic-plastic stability. This indicates the high reforestation potential of the degraded lands of the Oka basin, which makes it possible to include its forest areas in the global system of biosphere reserves. Two opposite mechanisms exhibiting the known buffer properties of the forest litter have been revealed. In response to the unfavourable impacts, the forest community switches from some leading processes of its functioning to others – from the level of autotrophic biogenesis to the level of detrital metabolism.

Hyperspectral Infrared Observations of Arctic Snow, Sea Ice, and Non-Frozen Ocean from the RV Polarstern during the MOSAiC Expedition October 2019 to September 2020

This study highlights hyperspectral infrared observations from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) collected as part of the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) deployment on the icebreaker RV Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. The ARM M-AERI directly measures the infrared radiance emission spectrum between 520 cm−1 and 3000 cm−1 (19.2–3.3 μm) at 0.5 cm−1 spectral resolution. These ship-based observations provide a valuable set of radiance data for the modeling of snow/ice infrared emission as well as validation data for the assessment of satellite soundings. Remote sensing using hyperspectral infrared observations provides valuable information on sea surface properties (skin temperature and infrared emissivity), near-surface air temperature, and temperature lapse rate in the lowest kilometer. Comparison of the M-AERI observations with those from the DOE ARM meteorological tower and downlooking infrared thermometer are generally in good agreement with some notable differences. Operational satellite soundings from the NOAA-20 satellite were also assessed using ARM radiosondes launched from the RV Polarstern and measurements of the infrared snow surface emission from the M-AERI showing reasonable agreement.

Constraining industrial ammonia emissions using hyperspectral infrared imaging

Atmospheric emissions of reactive nitrogen in the form of nitrogen dioxide (NO2) and ammonia (NH3) worsen air quality and upon deposition, dramatically affect the environment. Recent infrared satellite measurements have revealed that NH3 emitted by industries are an important and underestimated emission source. Yet, to assess these emissions, current satellite sounders are severely limited by their spatial resolution. In this paper, we analyse measurement data recorded in a series of imaging surveys that were conducted over industries in the Greater Berlin area (Germany). On board the aircraft were the Telops Hyper-Cam LW, targeting NH3 measurements in the longwave infrared at a resolution of 4 m and the SWING+ spectrometer targeting NO2 measurements in the UV–Vis at a resolution of 180 m.Two flights were carried out over German’s largest production facility of synthetic NH3, urea and other fertilizers. In both cases, a large NH3 plume was observed originating from the factory. Using a Gaussian plume model to take into account plume rise and dispersion, coupled with well-established radiative transfer and inverse methods, we retrieve vertical column densities. From these, we calculate NH3 emission fluxes using the integrated mass enhancement and cross-sectional flux methods, yielding consistent emissions of the order of 2200 t yr−1 for both flights, assuming constant fluxes across the year. These estimates are about five times larger than those reported in the European Pollutant Release and Transfer Register (E-PRTR) for this plant. In the second campaign, a co-emitted NO2 plume was measured, likely related to the production of nitric acid at the plant.A third flight was carried out over an area comprising the cities of Staßfurt and Bernburg. Several small NH3 plumes were seen, one over a production facility of mineral wool insulation, one over a sugar factory and two over the soda ash plants in Staßfurt and Bernburg. A fifth and much larger plume was seen to originate from the sedimentation basins associated with the soda ash plant in Staßfurt, indicating rapid volatilization of ammonium rich effluents. We use the different measurement campaigns to simulate measurements of Nitrosat, a potential future satellite sounder dedicated to the sounding of reactive nitrogen at a resolution of 500 m. We demonstrate that such measurements would allow accurately constraining emissions in a single overpass, overcoming a number of important drawbacks of current satellite sounders.

Stratospheric Temperature Observations by Narrow Bands Ultra-High Spectral Resolution Sounder from Nadir-Viewing Satellites

Accurate stratospheric temperature observations are crucial for weather forecasts and climate change studies. This paper discusses a precise measurement method for the stratospheric temperature profile using narrow bands with ultra-high spectral resolution from nadir-viewing satellites. First, the CO2 absorption band around 15 μm is selected as the major sounding source by the calculation and analysis of the temperature Jacobian and the atmospheric molecular spectra. Next, the influence of spectral resolution, spectral range and instrumental noise on the sounding capability is analyzed, and the sounding feasibility of the single spectral band and multiple spectral bands is discussed under the condition that the spaceborne long-wave infrared space heterodyne spectrometer (SHS) is selected as suggested sounder onboard the satellite. Finally, the optimal joint-sounding scheme of narrow bands is proposed. The temperature retrieval and validation show that the joint-sounding of two discontinuous narrow bands can realize the high precision measurement of the stratospheric temperature profile for the given spectral resolution, spectral range, and instrumental noise. When the sounder adopts two narrow bands (the regions of 666.87–676.44 cm−1 and 683.58–693.15 cm−1) and a spectral resolution of 0.03 cm−1, the retrieval accuracy (RMSE) is about 0.9 K over a pressure range of 200 to 0.7 hPa (11.5–50 km). This study will provide technical preparation for high-precision and low-cost satellite sounder design for stratospheric temperature observations.

Methods for Correction of the Altitude Electron-Density Profiles of the IRI Model for the Bottomside Ionosphere from Satellite Sounding Data

Methods for Correction of the Altitude Electron-Density Profiles of the IRI Model for the Bottomside Ionosphere from Satellite Sounding Data

Assessing the consistency of satellite-derived upper tropospheric humidity measurements

Abstract. Four upper tropospheric humidity (UTH) datasets derived from satellite sounders are evaluated to assess their consistency as part of the activities for the Global Energy and Water Exchanges (GEWEX) water vapor assessment project. The datasets include UTH computed from brightness temperature measurements of the 183.31±1 GHz channel of the Special Sensor Microwave – Humidity (SSM/T-2), Advanced Microwave Sounding Unit-B (AMSU-B), and Microwave Humidity Sounder (MHS) and from channel 12 of the High-resolution Infrared Radiation Sounder (HIRS). The four datasets are generally consistent in the interannual temporal and spatial variability of the tropics. Large positive anomalies peaked over the central equatorial Pacific region during El Niño events in the same phase with the increase of sea surface temperature (SST). Conversely, large negative anomalies were obtained during El Niño events when the tropical-domain average is taken. The weakened ascending branch of the Pacific Walker circulation in the western Pacific and the enhanced descending branches of the local Hadley circulation along the Pacific subtropics largely contributed to widespread drying areas and thus negative anomalies in the upper troposphere during El Niño events as shown in all four datasets. During a major El Niño event, UTH had higher correlations with the coincident precipitation (0.60 to 0.75) and with 200 hPa velocity potential (−0.42 to −0.64) than with SST (0.37 to 0.49). Due to differences in retrieval definitions and gridding procedures, there can be a difference of 3 %–5 % UTH between datasets on average, and larger magnitudes of anomaly values are usually observed in spatial maps of microwave UTH data. Nevertheless, the tropical-domain averaged anomalies of the datasets are close to each other with their differences being mostly less than 0.5 %, and more importantly the phases of the time series are generally consistent for variability studies.

ХАРАКТЕРИСТИКИ И СТРУКТУРА МЕЗОМАСШТАБНЫХ КОНВЕКТИВНЫХ СИСТЕМ НАД ЗАПАДНОЙ СИБИРЬЮ ПО ДАННЫМ ДИСТАНЦИОННЫХ НАБЛЮДЕНИЙ

Many natural hazards are associated with deep convective clouds. Among them, mesoscale convective systems characterized by a large size and a long duration are the most dangerous. The estimates of their area, cloud top height, moisture content, duration, and intensity of related thunderstorm activity for Western Siberia were obtained using the data of radio and optical (passive and active) satellite sounding (for the summer months in 2010-2019) and World Wide Lightning Location Network (WWLLN, 2016-2020).

Calculation of the absorption coefficient of air at different heights using the HITRAN and ACE-FTS databases

Subject of study. Increasing requirements for the accuracy of modeling the brightness characteristics of the atmosphere at different heights motivate the development of more detailed methods for the calculation of the absorption coefficient of air. Method. Modern databases of satellite sounding of the atmosphere that contain information on the volume fractions of air components at different heights in combination with a database of the parameters of the spectral lines of gases can be used in this task to calculate the spectral absorption coefficient. The possibility of specifying the geographic position of the height profiles of the air components (by specifying latitude and longitude) is an additional advantage of using the databases of satellite sounding. This method enables the differences in air compositions above different regions of the Earth to be considered. These databases usually provide information starting from a certain height; thus, databases of satellite sounding must be combined with the data obtained either from ground-based meteorological stations or using model distributions. The ACE-FTS database was used in this study, and it was combined with the standard atmosphere MODTRAN models at low heights. A filter for the ACE-FTS database was implemented using C++. The HITRAN database was used to calculate absorption coefficients. The ACE-FTS database provides data for 43 components of air, and the HITRAN database contains data for line-by-line calculation for 27 of these components and data on spectral absorption cross-sections for the remaining 16 components. Main results. A program for the calculation of the absorption coefficient of a multicomponent gas mixture was developed using C++. A Voigt profile was used in the line-by-line calculation, the effects of pressure and temperature on the line shift were considered, and line broadening owing to the following processes was considered: self-broadening, broadening resulting from interaction with water and carbon dioxide molecules, and broadening owing to interaction with other components of the air. The software explicitly considers the isotopic composition of molecules, thus enabling the calculation of not only the air mixture but also an arbitrary mixture with specified isotopic composition, information on which is in the HITRAN database. Moreover, the data of the high-temperature version HITEMP are considered. Practical significance. The combination of the ACE-FTS and HITRAN databases enables the calculation of a detailed profile of the spectral absorption coefficient of air for the specified month, temperature at the surface of the Earth, and geographic latitude and longitude, thus increasing the information content of the input data for the calculation of the brightness and transmission of the atmosphere at different heights. The data readout rate (parsing) and calculation speed of the developed program and the program HAPI implemented using Python are compared.

On the weekly cycle of atmospheric ammonia over European agricultural hotspots

The presence of a weekly cycle in the abundance of an atmospheric constituent is a typical fingerprint for the anthropogenic nature of its emission sources. However, while ammonia is mainly emitted as a consequence of human activities, a weekly cycle has never been detected in its abundances at large scale. We expose here for the first time the presence of a weekend effect in the NH3 total columns measured by the IASI satellite sounder over the main agricultural source regions in Europe: northwestern Europe (Belgium-the Netherlands-northwest Germany), the Po Valley, Brittany, and, to a lesser extent, the Ebro Valley. A decrease of 15% relative to the weekly mean is seen on Sunday–Monday observations in northwestern Europe, as a result of reduced NH3 emissions over the weekend. This is confirmed by in situ NH3 concentration data from the National Air Quality Monitoring Network in the Netherlands, where an average reduction of 10% is found around midnight on Sunday. The identified weekend effect presents a strong seasonal variability, with two peaks, one in spring and one in summer, coinciding with the two main (manure) fertilization periods. In spring, a reduction on Sunday–Monday up to 53 and 26% is found in the NH3 satellite columns and in situ concentrations, respectively, as fertilization largely drives atmospheric NH3 abundances at this time of the year.

Evaluating Satellite Sounders for Monitoring the Tropical Cyclone Environment in Operational Forecasting

Tropical cyclones can form over open ocean where in situ observations are limited, so forecasters rely on satellite observations to monitor their development and track. We explore the utility of an operational satellite sounding product for tropical forecasting by characterizing the products retrieval skill during research flights. Scientists from both the NOAA-Unique Combined Atmospheric Processing System (NUCAPS) research team and tropical cyclone communities collaborated to target relevant tropical cyclones during the campaign. This effort produced 130 dropsondes that are well-timed with satellite sounder overpasses over three different tropical cyclones and one Saharan Air Layer outbreak. For the combined infrared and microwave retrieval, the NUCAPS temperature has a root mean square error (RMSE) of 1.2 K near the surface (1000–600 mb) and 0.8 K in the mid-troposphere (600–300 mb), which is in line with global product requirements. The water vapor mixing ratio RMSE was 26% near the surface and 46% in the mid-troposphere. NUCAPS microwave-only retrievals can also be useful for cloudy scenes, with surface RMSE values of 4 K (temperature) and 23% (water vapor). Using information content analysis, we estimated that the vertical resolution near the surface was 1.7 km for the temperature retrievals and 2.2 km for the water vapor retrievals in this study. We discuss the feasibility of implementing NUCAPS in an operational forecasting setting, which requires rapid data delivery to forecaster software tools.

Observational Analyses of Dry Intrusions and Increased Ozone Concentrations in the Environment of Wildfires

In this study, atmospheric dynamical processes, which govern the intensification of wildfire activity and the associated increase in low-level ozone concentrations, were studied using images, advanced products and vertical profiles derived from satellite observations. The analyses confirm that the influence of deep stratospheric intrusions, identified in the satellite water vapor imagery, on a fire-risk area contributes to the increase in fire activity. The depth of dry stratospheric intrusions, the associated synoptic evolution and the enhanced low-level ozone concentrations caused by vertical transport of stratospheric air and/or related to biomass burning emissions were analyzed using satellite measurements from SEVIRI, IASI and CrIS instruments, complemented with surface observations near the wildfires’ locations. It is shown that the spatial and vertical resolutions of these soundings provide a way of identifying areas of enhanced ozone downwind of wildfires. Influences of the upper-troposphere dynamics and the wind field evolution as factors of uncertainty and complexity in studying the ozone production from wildfire emissions are considered. The combination of satellite soundings and satellite estimations of fire radiative energy and WV imagery may contribute to better understand the ozone enhancement associated with stratospheric intrusion and wildfire emissions.

Preliminary Assessment of MetOp-Based Temperature and Humidity Statistical Retrievals within the 3D-Var AROME-France Prediction System

Abstract The main objective of the study is to evaluate the feasibility and benefits of assimilating satellite temperature and humidity soundings (aka Level 2 or L2 profiles), instead of radiances, from the EUMETSAT Advanced Retransmission Service (EARS) into the AROME-France data assimilation system. The satellite soundings are operational forecast-independent retrievals that used the infrared sounder IASI in synergy with its companion microwave instruments AMSU-A and MHS on board the MetOp platforms. In this assimilation study, L2 profiles are used as pseudoradiosondes, discarding vertical error correlations and the instrument vertical sensitivity in the observation operator due to the lack of available averaging kernels. Three assimilation experiments were performed, the baseline (including all satellite radiances except those from IASI, AMSU-A, and MHS sounders), the control (with observations from the baseline plus IASI, AMSU-A, and MHS radiances), and the L2 experiment (with observations from the baseline and L2 temperature and humidity profiles). The assimilation runs cover the periods of the winter 2017 and summer 2018. The forecast skills of the three experiments are gauged against independent analyses and observations. Despite that the vertical observation operator is not accounted for in this study, it is found that L2 profile assimilation does not have a negative impact on 1-h temperature and humidity forecasts, especially in the midtroposphere. Their impacts are comparable in magnitude to the radiance ones in the operational AROME framework, except in terms of temperature and wind fields during winter where the impact is more negative than positive. These findings encourage further investigations.

Data Fusion of GEO FY-4A GIIRS and LEO Hyperspectral Infrared Sounders with Surface Observations: A Hong Kong Case Study

Abstract Hyperspectral infrared satellite observations from geostationary platforms allow for the retrieval of temperature and water vapor measurements with higher temporal and vertical resolution than was previously available. The Chinese satellite Fengyun-4A (FY-4A) includes the Geostationary Interferometric Infrared Sounder (GIIRS), which has the ability to measure vertical profiles of temperature and water vapor from space at times when ground-based upper-air soundings are not available and can fill an important need in short-range weather prediction. In this study, convective available potential energy (CAPE) and lifted index (LI), which are used for forecasting atmospheric instability, were computed using the SHARPpy algorithm used by the NWS Storm Prediction Center. However, remote infrared and microwave sensing is lacking detailed information in the boundary layer, so the addition of the NOAA Meteorological Assimilation and Data Ingest System (MADIS) surface data may be necessary in order to get accurate temperature and moisture measurement near the surface. This study uses 10–16 May 2019 in the coastal region near Hong Kong for evaluating the use of hourly surface observations combined with satellite soundings from FY-4A GIIRS at 2-h intervals. The GIIRS plus MADIS surface-based CAPE and LI estimates are compared to estimates derived from low-Earth-orbiting (LEO) SNPP and NOAA-20 from NOAA, MetOp from EUMETSAT, NWP reanalysis, and local radiosondes. In the case study, the 2-h sampling interval of the GIIRS geostationary sounder was able to capture the rapid transition (16 h) from a stable to an unstable atmosphere in both CAPE and LI. The use of surface observations with satellite soundings gave mixed results, possibly due to the complex terrain near Hong Kong.