Abstract The Ozone Monitoring Instrument (OMI) on the Aura satellite makes near‐daily measurements of solar spectral irradiance (SSI) at wavelengths between 265 and 500 nm for instrument calibration purposes. The low degradation and exceptional stability of OMI's calibration during its lifetime facilitates the creation of a new 18‐year OMI Version 7 data set. This data set presented here, which extends our previous data set by more than six years, is constructed using an improved OMI degradation model, and enables discussion of SSI variability during the extended 2009 solar activity minimum and subsequent Solar Cycles 24 and 25. OMI observations of solar irradiance variability in the mid‐ultraviolet (265–300 nm), near‐ultraviolet (300–400 nm), and visible (400–500 nm) spectral regions, consistent with concurrent measurements from other satellite instruments, show that, contrary to initial predictions, Solar Cycle 25 is significantly more active than Solar Cycle 24. Solar activity indices created from OMI SSI observations agree with both satellite and ground‐based indices, and are similarly higher in Solar Cycle 25 than 24. We demonstrate good agreement between the OMI irradiance observations and the new observation‐based NOAA‐NASA‐LASP (NNLSSI1) model of solar irradiance variability, including during Solar Cycle 25. The agreement is even better when the model is revised using an improved facular index that is consistent with OMI activity indices. We use the revised NNLSSI1 rev 1 model reconstruction of solar irradiance in the past century to make a simple statistical projection of SSI variability during the remaining portion of Solar Cycle 25 and beyond.
For over 26 years, the MODIS instrument on the Terra platform has generated a broad range of scientific products, enabling the remote sensing community worldwide for the study of many geophysical parameters of the Earth's system. Together with the complementary observations from the MODIS instrument on the Aqua platform, a continuous and consistent data record dating back to the year 2000 has been generated. MODIS, a major advance over its heritage sensors in terms of its spectral, spatial, and temporal resolutions, provides Earth scene imagery via 36 spectral bands ranging from 0.4 to 14.4 mu m at three different spatial resolutions with a wide swath of 2330 km. In addition, significantly enhanced are dedicated calibration efforts to help produce and maintain MODIS data quality through its entire mission. We present a comprehensive summary of Terra MODIS operations, the calibration strategies developed and implemented, and its on-orbit performance over the 26 years of successful operation. Terra MODIS has maintained radiometric uncertainties of less than 2% for reflective solar bands and better than 0.1 K for thermal emissive bands over its 26-year mission, far exceeding its 6-year design life. The mission's success in maintaining long-term data quality demonstrates the critical importance of comprehensive on-board calibration systems and continuous performance monitoring for multiyear Earth observations. This calibration heritage provides essential guidance for designing future multidecadal Earth observing missions.
Abstract We describe a Geometry‐dependent surface Lambertian‐Equivalent Reflectivity (GLER) climatology developed to support operational retrievals for the Tropospheric Emissions: Monitoring of Pollution (TEMPO) mission. This data set provides monthly and hourly surface reflectance for snow‐free land, snow‐covered land, and oceanic regions. The set is constructed by integrating MODIS MCD43C1/C2 bidirectional reflectance distribution function (BRDF) parameters, snow cover information, and radiative transfer simulations. A Factor‐Analysis spectral reconstruction method, constrained by spectral priors from the USGS spectral library and the SCIAMACHY LER data set, was applied to extend discrete MODIS four‐band reflectance over land to a near‐continuous spectral range (335–900 nm), covering most of the spectral range of TEMPO. The ocean climatology GLER was simulated using a Cox–Munk surface slope distribution model coupled with the VLIDORT model. Preliminary comparisons with the TROPOMI directionally dependent LER (DLER) empirical data set demonstrate strong seasonal consistency at a local solar time of 13:30. Summer mean differences generally remain within ±0.01, while larger winter biases (up to 0.03) are primarily attributed to extreme solar geometries, sub‐pixel residual snow, and adjacency pixel effects. This GLER climatology currently serves as a crucial input for TEMPO Level 2 operational algorithms, supporting retrievals for nitrogen dioxide, formaldehyde, and ozone, as well as cloud parameter estimations.
The evolution of organic aerosol (OA) composition and aerosol size distributions within smoke plumes are uncertain due to variability in the rates of OA evaporation/condensation and coagulation within a plume. It remains unclear how the evolution varies across different parts of individual plumes. We use a large eddy simulation model coupled with aerosol‐microphysics and radiation models to simulate the Williams Flats fire sampled during the Fire Influence on Regional to Global Environments and Air Quality field campaign. At aircraft altitude, the model captures observed aerosol changes through 4 hr of aging. The model evolution of primary OA (POA), oxidized POA (OPOA), and secondary OA (SOA) shows that >90% of the SOA formation occurs before the first transect (∼40 min of aging). Lidar observations and the model show a significant amount of smoke in the planetary boundary layer (PBL) and free troposphere (FT) with the model having equal amounts of smoke in the PBL and FT. Due to faster initial dilution, PBL concentrations are more than a factor of two lower than the FT concentrations, resulting in slower coagulational growth in the PBL. A 20 K temperature decrease with height in the PBL influences faster POA evaporation near the surface, while net OA evaporation in the FT is driven by continued dilution after the first aircraft transect. Net OA condensation in the PBL after the first transect is the result of areas with higher OH concentration leading to OPOA formation. Our results motivate the need for systematic observations of the vertical gradients of aerosol size and composition within smoke plumes.
