Satellite Sounder Observations of Contrasting Tropospheric Moisture Transport Regimes: Saharan Air Layers, Hadley Cells, and Atmospheric Rivers

Abstract

This paper examines the performance of satellite sounder atmospheric vertical moisture profiles under tropospheric conditions encompassing moisture contrasts driven by convection and advection transport mechanisms, specifically Atlantic Ocean Saharan air layers (SALs), tropical Hadley cells, and Pacific Ocean atmospheric rivers (ARs). Operational satellite sounder moisture profile retrievals from the Suomi National Polar-Orbiting Partnership (SNPP) NOAA Unique Combined Atmospheric Processing System (NUCAPS) are empirically assessed using collocated dedicated radiosonde observations (raobs) obtained from ocean-based intensive field campaigns. The raobs from these campaigns provide uniquely independent correlative truth data not assimilated into numerical weather prediction (NWP) models for satellite sounder validation over oceans. Although ocean cases are often considered “easy” by the satellite remote sensing community, these hydrometeorological phenomena present challenges to passive sounders, including vertical gradient discontinuities (e.g., strong inversions), as well as persistent uniform clouds, aerosols, and precipitation. It is found that the operational satellite sounder 100-layer moisture profile NUCAPS product performs close to global uncertainty requirements in the SAL/Hadley cell environment, with biases relative to raob within 10% up to 350 hPa. In the more difficult AR environment, bias relative to raob is found to be within 20% up to 400 hPa. In both environments, the sounder moisture retrievals are comparable to NWP model outputs, and cross-sectional analyses show the capability of the satellite sounder for detecting and resolving these tropospheric moisture features, thereby demonstrating a near-real-time forecast utility over these otherwise raob-sparse regions.

Validation of Carbon Trace Gas Profile Retrievals from the NOAA-Unique Combined Atmospheric Processing System for the Cross-Track Infrared Sounder

“…These maps show the excellent global zonal representation of the validation sample, albeit primarily over oceans. Although the NUCAPS retrievals may generally be "easier" (i.e., more accurate) over ocean surfaces (i.e., where the surface emission/reflectance properties are relatively uniform and well characterized relative to the retrieval uncertainties) [67], this is not always the case [68], and operational satellite data have been demonstrated to make their greatest impact over the data-sparse oceans [69]. Thus the ATom data are of singular value for our validation.…”

<i>A Tale of Two Dust Storms</i>: Analysis of a Complex Dust Event in the Middle East

“…Owing to the projection of the cross-track scanning sensor footprints, spatial resolution ranges from ~50 km at nadir to ~70 x 134 km at scan edge. Nalli et al (2016) demonstrate that NUCAPS water vapor profiles compare favorably to radiosonde data and to numerical weather prediction models in terms of moisture magnitude and gradients in a variety of atmospheric flows. Fig.…”

Investigating NUCAPS Skill in Profiling Saharan Dust for Near-Real-Time Forecasting

“…NU-CAPS can retrieve multiple variables at different vertical pressure levels by only using a subset of spectral channels. The channels are selected such that they are sensitive to the target variables while maintaining as much spectral independence from other retrieved parameters as possible [13]. Furthermore, the order that variables are retrieved helps to further stabilize the solution, as some atmospheric constituents are highly sensitive to other variables.…”

“…Since radiosondes on a global scale are relatively sparse temporally speaking (and spatially sparse over oceans), the ability of these soundings to fill in gaps is invaluable. NUCAPS does not directly measure African mineral dust outflow into the open water of the Atlantic basin, but it can identify SAL conditions associated with dust [13], as well as atmospheric conditions conducive to dust transport. Saharan dust is typically confined to the lowest layer of the atmosphere [14,15].…”