Gene Francis

Global estimates of gravity wave momentum flux from High Resolution Dynamics Limb Sounder observations

analyzed to derive global properties of gravity waves. We describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs, the wave vertical wavelength as a function of height, and the horizontal wave number along the line joining each profile pair. The analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis. We examine global distributions of these gravity wave properties in the monthly mean and on an individual day, and we also show sample instantaneous wave events observed by HIRDLS. The results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow. The high vertical and horizontal resolution afforded by the HIRDLS measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail. Mountain wave observations show clear propagation to altitudes in the mesosphere.

Initial validation of ozone measurements from the High Resolution Dynamics Limb Sounder

Comparisons of the latest High Resolution Dynamics Limb Sounder (HIRDLS) ozone retrievals (v2.04.09) are made with ozonesondes, ground-based lidars, airborne lidar measurements made during the Intercontinental Chemical Transport Experiment–B, and satellite observations. A large visual obstruction blocking over 80% of the HIRDLS field of view presents significant challenges to the data analysis methods and implementation, to the extent that the radiative properties of the obstruction must be accurately characterized in order to adequately correct measured radiances. The radiance correction algorithms updated as of August 2007 are used in the HIRDLS v2.04.09 data presented here. Comparisons indicate that HIRDLS ozone is recoverable between 1 and 100 hPa at middle and high latitudes and between 1 and 50 hPa at low latitudes. Accuracy of better than 10% is indicated between 1 and 30 hPa (HIRDLS generally low) by the majority of the comparisons with coincident measurements, and 5% is indicated between 2 and 10 hPa when compared with some lidars. Between 50 and 100 hPa, at middle and high latitudes, accuracy is 10–20%. The ozone precision is estimated to be generally 5–10% between 1 and 50 hPa. Comparisons with ozonesondes and lidars give strong indication that HIRDLS is capable of resolving fine vertical ozone features (1–2 km) in the region between 1 and 50 hPa. Development is continuing on the radiance correction and the cloud detection and filtering algorithms, and it is hoped that it will be possible to achieve a further reduction in the systematic bias and an increase in the measurement range downward to lower heights (at pressures greater than 50–100 hPa).

Overview and characterization of retrievals of temperature, pressure, and atmospheric constituents from the High Resolution Dynamics Limb Sounder (HIRDLS) measurements

Received 18 February 2009; revised 22 April 2009; accepted 26 June 2009; published 23 October 2009. [1] The retrieval algorithm for the High Resolution Dynamics Limb Sounder (HIRDLS) instrument onboard NASA’s Earth Observing System (EOS) Aura satellite is presented. The algorithm is based on optimal estimation theory, using a modified Levenberg-Marquardt approach for the iterative solution. Overview of the retrieval scheme, convergence criteria, and the forward models is given. Treatments of clouds and aerosols as well as line-of-sight gradients in temperature are described. The retrievals are characterized by high vertical resolution of 1 km and negligible a priori contribution for all products in regions of high signal-to-noise ratio (SNR) (most of the retrieval ranges). It is shown that these characteristics hold for all latitudes along a HIRDLS orbit. The weighting functions are narrow and show good sensitivity to temperature or gas perturbations in regions of high SNR. The retrieval error predicted by the algorithm consists of radiometric noise, pointing jitter error, smoothing error, and forward model error. For temperature, these components are shown for a midlatitude profile as well as for a full orbit. The predicted temperature error varies from 0.5 K to 0.8 K from the upper troposphere to the stratopause region, consistent with the empirical estimates given by Gille et al. (2008). For O3 and HNO3, the predicted errors and their useful pressure ranges are, respectively, 10–5% from 50 to 1 hPa and 5–10% from 100 to 10 hPa. These results are based on version V004 of the retrieved data, released in August 2008 to the Goddard Earth Sciences Data and Information Services Center (http://daac.gsfc.nasa.gov).

Improvements to the correlated‐k radiative transfer method: Application to satellite infrared sounding

This paper presents a new radiative transfer model based on the correlated-k technique that is particularly suitable for applications associated with broadband infrared satellite remote sounding of the atmosphere. We describe new developments to the approach which improve the accuracy of correlated-k distribution radiative transfer calculations. These include methods to model an instrument response function, spectral line overlap for multiple gases, and the spectral variation of solar and thermal source functions. We also describe an approach to improving vertical spectral correlation along ray paths through a nonhomogeneous atmosphere. For a radiative transfer model to be efficient as the forward model of a retrieval scheme, the calculation of analytical Jacobians is particularly important. This is implemented in the model using a variation on the correlated-k approach. The application of the new model, RADCKD, is demonstrated with example calculations for the EOS Terra satellite Measurements of Pollution in the Troposphere (MOPITT) instrument.

Operational validation of the MOPITT instrument optical filters

Abstract Optical bandpass filters in the Measurements of Pollution in the Troposphere (MOPITT) satellite remote sensing instrument selectivity limit the throughput radiance to absorptive spectral bands associated with the satellite-observed trace gases CO and CH4. Precise specification of the spectral characteristics of these filters is required to optimize retrieval accuracy. The effects and potential causes of spectral shifts in the optical bandpass filter profiles are described. Specifically, a shift in the assumed bandpass profile produces a relative bias between the calibrated satellite radiances and the corresponding values calculated by an instrument-specific forward radiative transfer model. Conversely, it is shown that the observed bias (as identified and quantified using operational MOPITT satellite radiance data) can be used to determine the relative spectral shift between the nominal (prelaunch) filter profiles and the true operational (in orbit) profiles. Revising both the radiance calibratio...

Effects of a Spectral Surface Reflectance on Measurements of Backscattered Solar Radiation: Application to the MOPITT Methane Retrieval

Abstract The amount of solar radiation emerging from the top of the atmosphere is strongly influenced by the reflectance of the underlying surface. For this reason, some information about the magnitude and the spectral variability of the surface reflectance typically has to be included in the retrieval of atmospheric parameters from reflected solar radiation measurements. Sufficient information about the surface reflectance properties is rarely available, and the integration of this effect in the retrieval might turn out to be a challenge, especially for broadband instruments. In this paper the focus is on the Measurements of Pollution in the Troposphere (MOPITT) remote sensing instrument. Theoretical studies are performed to investigate how a spectrally varying surface reflectance might impact the retrieval of the total column amount of methane from MOPITT radiance measurements, and the current findings are compared to observed biases. However, the findings present herein might be valuable and applicable...

Development of special corrective processing of HIRDLS data, and early validation

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on NASAs Aura spacecraft on 15 July 2004. When activation was completed 25 days later, it was discovered that the measured radiances were very different from those that were expected. After a long series of analyses and diagnostic tests, the cause was confirmed to be a blockage that covers much of the front aperture, preventing even one completely clear view of the atmosphere. In this paper the steps required to correct the radiances for the effects of the blockage are noted. These are calibrating the radiances, removing the effects of the blockage oscillating, and the radiance coming from the blockage, correcting for the effects of the partial aperture, and filtering the noise. The paper describes the algorithms needed, and presents the results of their application. The success of the procedures will be demonstrated by the quality of the resulting radiances and retrieved profiles of temperature and trace species. The difficulties that have been eliminated, and that still remain are noted, along with plans for further improvement. Finally, the scientific implications are briefly discussed.

Assessing the impacts of assimilating IASI and MOPITT CO retrievals using CESM-CAM-chem and DART

We show the results and evaluation with independent measurements from assimilating both MOPITT (Measurements Of Pollution In The Troposphere) and IASI (Infrared Atmospheric Sounding Interferometer) retrieved profiles into the Community Earth System Model (CESM). We used the Data Assimilation Research Testbed ensemble Kalman filter technique, with the full atmospheric chemistry CESM component Community Atmospheric Model with Chemistry. We first discuss the methodology and evaluation of the current data assimilation system with coupled meteorology and chemistry data assimilation. The different capabilities of MOPITT and IASI retrievals are highlighted, with particular attention to instrument vertical sensitivity and coverage and how these impact the analyses. MOPITT and IASI CO retrievals mostly constrain the CO fields close to the main anthropogenic, biogenic, and biomass burning CO sources. In the case of IASI CO assimilation, we also observe constraints on CO far from the sources. During the simulation time period (June and July 2008), CO assimilation of both instruments strongly improves the atmospheric CO state as compared to independent observations, with the higher spatial coverage of IASI providing better results on the global scale. However, the enhanced sensitivity of multispectral MOPITT observations to near surface CO over the main source regions provides synergistic effects at regional scales.

Final correction algorithms for HIRDLS version 7 data

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is a 21-channel limb scanning infrared radiometer, designed to make global measurements of temperature, ozone, water vapor, eight other gases and aerosols from 8 to as high as 80 km. with 1 km. vertical resolution. During launch on NASA’S Aura satellite a piece of interior lining material became lodged in the foreoptics, reducing the effective aperture by 80-95%, and inserting another signal into the system. The HIRDLS team has worked for several years to develop corrections for these effects, and recover as many as possible of the planned capabilities. This talk describes the last and probably final set of algorithms to recover the planned species. Early work developed corrections for channels with large radiances allowing temperature and ozone to be retrieved. Subsequent work has concentrated on refining these to allow species such as nitric acid, chlorofluorocarbons 11 & 12, nitrogen dioxide, N2O5, chlorine nitrate, nitrous oxide and water vapor to be recovered. Effort has gone into studying, then parameterizing in an adaptive way, the quasi-regular way the signal from the blockage varies with time during an orbit and during the mission. Several recent improvements are described. Results of these corrections show improvements in the retrieved products.

Channel radiance calculations for MOPITT forward modeling and operational retrievals

The MOPITT (Measurement of Pollution in the Troposphere) instrument, to be launched on the Earth Observing System Terra platform, employs gas-correlation spectroscopy to measure profiles of tropospheric carbon monoxide and the total column of methane. The modeling of the instrument, and the associated radiative transfer, comprise the forward model employed in the retrieval calculations. The MOPITT forward model has been implemented through a hierarchy of radiation codes whose salient features are reviewed here.