Using nighttime observations from Visible Infrared Imager Radiometer Suite (VIIRS) Day/Night band (DNB), the characteristics of artificial light sources are evaluated as functions of observation conditions, and incremental improvements are documented on nighttime aerosol retrievals using VIIRS DNB data on a regional scale. We find that the standard deviation of instantaneous radiance for a given artificial light source is strongly dependent upon the satellite viewing angle but is weakly dependent on lunar fraction and lunar angle. Retrieval of nighttime aerosol optical thickness (AOT) based on the novel use of these artificial light sources is demonstrated for three selected regions (United States, Middle East and India) during 2015. Reasonable agreement is found between nighttime AOTs from the VIIRS DNB and temporally adjacent daytime AOTs from the AErosol RObotic NETwork (AERONET) as well as from coincident nighttime AOT retrievals from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), indicating the potential of this method to begin filling critical gaps in diurnal AOT information at both regional and global scales. Issues related to cloud, snow and ice contamination during the winter season, as well as data loss due to the misclassification of thick aerosol plumes as clouds, must be addressed to make the algorithm operationally robust.

Lofted mineral dust over data-sparse regions presents considerable challenges to satellite-based remote sensing methods and numerical weather prediction alike. The southwest Asia domain is replete with such examples, with its diverse array of dust sources, dust mineralogy, and meteorologically driven lofting mechanisms on multiple spatial and temporal scales. A microcosm of these challenges occurred over 3–4 August 2016 when two dust plumes, one lofted within an inland dry air mass and another embedded within a moist air mass, met over the southern Arabian Peninsula. Whereas conventional infrared-based techniques readily detected the dry air mass dust plume, they experienced marked difficulties in detecting the moist air mass dust plume, becoming apparent when visible reflectance revealed the plume crossing over an adjacent dark water background. In combining information from numerical modeling, multi-satellite and multi-sensor observations of lofted dust and moisture profiles, and idealized radiative transfer simulations, we develop a better understanding of the environmental controls of this event, characterizing the sensitivity of infrared-based dust detection to column water vapor, dust vertical extent, and dust optical properties. Differences in assumptions of dust complex refractive index translate to variations in the sign and magnitude of the split-window brightness temperature difference commonly used for detecting mineral dust. A multi-sensor technique for mitigating the radiative masking effects of water vapor via modulation of the split-window dust-detection threshold, predicated on idealized simulations tied to these driving factors, is proposed and demonstrated. The new technique, indexed to an independent description of the surface-to-500 hPa atmospheric column moisture, reveals parts of the missing dust plume embedded in the moist air mass, with the best performance realized over land surfaces.

The detection and characterization of aerosols are inherently limited at night because the important information provided by visible spectrum observations is not available and infrared bands have limited sensitivity to aerosols. The VIIRS Day–Night Band (DNB) onboard the Suomi-NPP satellite is a first-of-its-kind calibrated sensor capable of collecting visible and near-infrared observations during both day and night. Multiple studies have suggested that anthropogenic light emissions such as those from cities and gas flares may be useable as light sources for the retrieval of atmospheric properties, including cloud and aerosol optical depth. However, their use in this capacity requires proper characterization of their intrinsic variation, which represents a source of retrieval uncertainty. In this study we use 18 months of cloud-cleared VIIRS data collected over five selected geographic domains to assess the stability of anthropogenic light emissions and their response to varied satellite and lunar geometries. Time series are developed for each location in each domain for DNB radiance, four infrared channels, and satellite and lunar geometric variables, and spatially resolved correlation coefficients are computed between DNB radiance and each of the other variables. This analysis finds that while many emissive light sources are too unstable to be used reliably for atmospheric retrievals, some sources exhibit a sufficient stability (relative standard deviation <20 %). Additionally, we find that while the radiance variability of surrounding surfaces (i.e., unpopulated land and ocean) is largely dependent on lunar geometry, the anthropogenic light sources are more strongly correlated with satellite viewing geometry. Understanding the spatially resolved relationships between DNB radiance and other parameters is a necessary first step towards characterizing anthropogenic light emissions and establishes a framework for a model to describe variability in a more general sense.

This high-resolution numerical modeling study investigates the potential range of impact of surface-lofted dust aerosols on the mean radiative fluxes and temperature changes associated with a dust-lofting episode over the Arabian Peninsula (2–5 August 2016). Assessing the potential for lofted dust to impact the radiation budget and temperature response in regions of the world that are prone to intense dust storms is important due to the impact of such temperature perturbations on thermally driven mesoscale circulations such as sea breezes and convective outflows. As such, sensitivity simulations using various specifications of the dust-erodible fraction were performed using two high-resolution mesoscale models that use similar dust-lofting physics based on threshold friction wind velocity and soil characteristics. The dust-erodible fraction, which represents the fraction (0.0 to 1.0) of surface soil that could be mechanically lifted by the wind and controls the location and magnitude of surface dust flux, was varied for three experiments with each model. The “Idealized” experiments, which used an erodible fraction of 1.0 over all land grid cells, represent the upper limit on dust lofting within each modeling framework, the “Ginoux” experiments used a 1∘ resolution, spatially varying erodible fraction dataset based on topographic depressions, and the “Walker” experiments used satellite-identified, 1 km resolution data with known lofting locations given an erodible fraction of 1.0. These simulations were compared with a “No-Dust” experiment in which no dust aerosols were permitted. The use of erodible fraction databases in the Ginoux and Walker simulations produced similar dust loading which was more realistic than that produced in the Idealized lofting simulations. Idealized lofting in this case study generated unrealistically large amounts of dust compared with observations of aerosol optical depth (AOD) due to the lack of locational constraints. Generally, the simulations with enhanced dust mass via surface lofting experienced reductions in daytime insolation due to aerosol scattering effects as well as reductions in nighttime radiative cooling due to aerosol absorption effects. These radiative responses were magnified with increasing amounts of dust loading. In the Idealized simulation with extreme (AOD > 5) dust amounts, these radiative responses suppressed the diurnal temperature range. In the Ginoux and Walker simulations with moderate (AOD ∼1–3) amounts of lofted dust, the presence of dust still strongly impacted the radiative fluxes but only marginally modified the low-level temperature. The dust-induced near-surface temperature change was limited due to competing thermal responses to changes in the net radiative fluxes and the dust-layer radiative heating rates. Compared to the Ginoux simulation, the use of increased resolution in dust-erodible fraction inventories in the Walker simulations led to enhanced fine-scale horizontal variability in lofted dust and a modest increase in the mean dust concentration profile and radiative or thermal responses. This study discusses the utility of using high-resolution dust source databases for simulating lofted dust, the need for greater spatial coverage of in situ aerosol observations in dust-prone regions, the impacts of dust on the local radiation budget and surface thermal conditions, and the potential dust radiative impacts on thermally driven mesoscale features.

Visible/Infrared Imaging Radiometer Suite (VIIRS) Imagery from the Suomi National Polar-orbiting Partnership (S-NPP) satellite is the finest spatial resolution (375 m) multi-spectral imagery of any operational meteorological satellite to date. The Imagery environmental data record (EDR) has been designated as a Key Performance Parameter (KPP) for VIIRS, meaning that its performance is vital to the success of a series of Joint Polar Satellite System (JPSS) satellites that will carry this instrument. Because VIIRS covers the high-latitude and Polar Regions especially well via overlapping swaths from adjacent orbits, the Alaska theatre in particular benefits from VIIRS more than lower-latitude regions. While there are no requirements that specifically address the quality of the EDR Imagery aside from the VIIRS SDR performance requirements, the value of VIIRS Imagery to operational users is an important consideration in the Cal/Val process. As such, engaging a wide diversity of users constitutes a vital part of the Imagery validation strategy. The best possible image quality is of utmost importance. This paper summarizes the Imagery Cal/Val Team’s quality assessment in this context. Since users are a vital component to the validation of VIIRS Imagery, specific examples of VIIRS imagery applied to operational needs are presented as an integral part of the post-checkout Imagery validation.

Using nighttime observations from Visible/Infrared Imager/Radiometer Suite (VIIRS) Day/Night band (DNB), the characteristics of artificial light sources are evaluated as functions of observation conditions and incremental improvements are documented on nighttime aerosol retrievals using VIIRS DNB data on a regional scale. We find that the standard deviation of instantaneous radiance for a given artificial light source is strongly dependent upon the satellite viewing angle, but is weakly dependent on lunar fraction and lunar angle. Retrieval of nighttime aerosol optical thickness (AOT) based on the novel use of these artificial light sources is demonstrated for three selected regions (United States, Middle East, and India) during 2015. Reasonable agreements are found between nighttime AOTs from VIIRS DNB and temporally adjacent daytime AOTs from AErosol RObotic NETwork (AERONET) as well as from coincident nighttime AOT retrievals from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), indicating the potential of this method to begin filling critical gaps in diurnal AOT information at both regional and global scales. Issues related to cloud, snow, and ice contamination during the winter season, as well as data loss due to the misclassification of thick aerosol plumes as clouds, must be addressed to make the algorithm operationally robust.