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M. J. Uddstrom and L. M. McMillin

Abstract

The National Environmental Satellite Data and Information Service (NESDIS) collocation data archive of satellite and radiosonde measurements is used to investigate errors in in situ radiosonde data and a NESDIS-like radiative transfer forward model. It is shown that the radiative transfer model errors have a strong airmass dependence and that these errors are not primarily due to nonrepresentativeness or radiosonde errors. However, errors in the in situ data do exist. For example, the National Meteorological Center radiosonde radiation adjustment algorithm in use during the period of data collection (1989–90) does not appear to provide adjustments of uniform quality across radiosonde sounding systems. The total system noise appropriate for use in retrieval algorithms is shown to vary from values close to the radiometer noise equivalent temperature difference (NEΔT) specifications for stratospheric channels to several times the NEΔT values for lower-tropospheric channels. Because of the significant discrepancies between measured and modeled radiances for the two most opaque water vapor sounding channels of the TIROS Operational Vertical Sounder, their use in a physical retrieval algorithm is considered problematic. Evidence for errors in NESDIS cloud-cleared (equivalent clear column) radiance temperature estimates is presented.

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M. J. Uddstrom and L. M. McMillin

Abstract

To utilize satellite radiance sounding data, in either explicit or implicit retrieval algorithms, a proper understanding of the noise in the measurements is required. Conventionally, to define the expected accuracy of atmospheric profiles inferred from sounder data, instrument noise equivalent temperature difference (NEΔT) noise specifications have been used to simulate spacecraft data. Here it is demonstrated that NEΔT noise specifications are inappropriate for this purpose. Instead, total system noise estimates should be employed since use of sounding data in any type of physical retrieval algorithm implies application of a radiative transfer model, which in turn must be “calibrated” against in situ and satellite data.

It is demonstrated that the accuracy of atmospheric retrievals inferred from the TIROS Operational Vertical Sounder radiometers is limited by the total system noise rather than NEΔT noise, and that modeled radiance temperatures perturbed by Gaussian total system noise very nearly replicate the accuracy statistics of retrievals computed from satellite measurements. The implications of these results for planned high-resolution infrared sounding instruments are briefly discussed.

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M. J. Uddstrom and D. Q. Wark

Abstract

A new approach is presented to the problem of specifying constraints on retrieval estimators used to calculate vertical temperature profiles from satellite measurements of upwelling radiance. An unsupervised classification scheme determines the typical shapes of temperature profiles that represent meteorologically significant events in some large ensemble of profiles. A data base for this purpose is developed, and a set of typical shape functions (TSFs) calculated to represent the sample. The TSFs are used to specify a radiance classifier which, given a radiance observation, defines the TSF class and thereby the constraints upon the retrieval estimator. An example is given, using simulated 15 μm data for the NOAA-6 TOVS. Preliminary calculations with synthetic radiance data indicate that an optimum inverse retrieval estimator using TSF-defined constraints results in rms differences that are approximately 50% better than those for a truncated eigenvector expansion regression estimator using zonally defined statistics; improvement in the region of the midlatitude tropopause is greater than 50%.

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Ronald B. Smith, Alison D. Nugent, Christopher G. Kruse, David C. Fritts, James D. Doyle, Steven D. Eckermann, Michael J. Taylor, Andreas Dörnbrack, M. Uddstrom, William Cooper, Pavel Romashkin, Jorgen Jensen, and Stuart Beaton

Abstract

During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) project in June and July 2014, the Gulfstream V research aircraft flew 97 legs over the Southern Alps of New Zealand and 150 legs over the Tasman Sea and Southern Ocean, mostly in the low stratosphere at 12.1-km altitude. Improved instrument calibration, redundant sensors, longer flight legs, energy flux estimation, and scale analysis revealed several new gravity wave properties. Over the sea, flight-level wave fluxes mostly fell below the detection threshold. Over terrain, disturbances had characteristic mountain wave attributes of positive vertical energy flux (EFz), negative zonal momentum flux, and upwind horizontal energy flux. In some cases, the fluxes changed rapidly within an 8-h flight, even though environmental conditions were nearly unchanged. The largest observed zonal momentum and vertical energy fluxes were MFx = −550 mPa and EFz = 22 W m−2, respectively.

A wide variety of disturbance scales were found at flight level over New Zealand. The vertical wind variance at flight level was dominated by short “fluxless” waves with wavelengths in the 6–15-km range. Even shorter scales, down to 500 m, were found in wave breaking regions. The wavelength of the flux-carrying mountain waves was much longer—mostly between 60 and 150 km. In the strong cases, however, with EFz > 4 W m−2, the dominant flux wavelength decreased (i.e., “downshifted”) to an intermediate wavelength between 20 and 60 km. A potential explanation for the rapid flux changes and the scale “downshifting” is that low-level flow can shift between “terrain following” and “envelope following” associated with trapped air in steep New Zealand valleys.

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David C. Fritts, Ronald B. Smith, Michael J. Taylor, James D. Doyle, Stephen D. Eckermann, Andreas Dörnbrack, Markus Rapp, Bifford P. Williams, P.-Dominique Pautet, Katrina Bossert, Neal R. Criddle, Carolyn A. Reynolds, P. Alex Reinecke, Michael Uddstrom, Michael J. Revell, Richard Turner, Bernd Kaifler, Johannes S. Wagner, Tyler Mixa, Christopher G. Kruse, Alison D. Nugent, Campbell D. Watson, Sonja Gisinger, Steven M. Smith, Ruth S. Lieberman, Brian Laughman, James J. Moore, William O. Brown, Julie A. Haggerty, Alison Rockwell, Gregory J. Stossmeister, Steven F. Williams, Gonzalo Hernandez, Damian J. Murphy, Andrew R. Klekociuk, Iain M. Reid, and Jun Ma

Abstract

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The core DEEPWAVE field phase took place from May through July 2014 using a comprehensive suite of airborne and ground-based instruments providing measurements from Earth’s surface to ∼100 km. Austral winter was chosen to observe deep GW propagation to high altitudes. DEEPWAVE was based on South Island, New Zealand, to provide access to the New Zealand and Tasmanian “hotspots” of GW activity and additional GW sources over the Southern Ocean and Tasman Sea. To observe GWs up to ∼100 km, DEEPWAVE utilized three new instruments built specifically for the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) Gulfstream V (GV): a Rayleigh lidar, a sodium resonance lidar, and an advanced mesosphere temperature mapper. These measurements were supplemented by in situ probes, dropsondes, and a microwave temperature profiler on the GV and by in situ probes and a Doppler lidar aboard the German DLR Falcon. Extensive ground-based instrumentation and radiosondes were deployed on South Island, Tasmania, and Southern Ocean islands. Deep orographic GWs were a primary target but multiple flights also observed deep GWs arising from deep convection, jet streams, and frontal systems. Highlights include the following: 1) strong orographic GW forcing accompanying strong cross-mountain flows, 2) strong high-altitude responses even when orographic forcing was weak, 3) large-scale GWs at high altitudes arising from jet stream sources, and 4) significant flight-level energy fluxes and often very large momentum fluxes at high altitudes.

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