Comparison of ECMWF analyses with GPS radio occultations from CHAMP

Schmidt, T.; Wickert, Jens; Heise, S.; Flechtner, Frank; Fagiolini, Elisa; Schwarz, Gottfried; Zenner, L.; Gruber, Th.

doi:10.5194/angeo-26-3225-2008

Cited by 12 publications

(5 citation statements)

References 26 publications

(34 reference statements)

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“…They found that the difference introduced by the application of vertical instead of horizontal filtering exceeds the differences between data sets applying the same method significantly. Schmidt et al (2016) confirmed that different techniques (in particular vertical spectral filtering versus horizontal S-transform analysis) have a large impact on the global gravity wave activity results, especially comparing gravity wave potential energy densities and gravity wave momentum flux estimates. In addition, they strongly recommend to use horizontal filtering for the detrending.…”

Section: Introductionmentioning

confidence: 61%

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

et al. 2020

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Abstract. Gravity waves are important drivers of dynamic processes in particular in the middle atmosphere. To analyse atmospheric data for gravity wave signals, it is essential to separate gravity wave perturbations from atmospheric variability due to other dynamic processes. Common methods to separate small-scale gravity wave signals from a large-scale background are separation methods depending on filters in either the horizontal or vertical wavelength domain. However, gravity waves are not the only process that could lead to small-scale perturbations in the atmosphere. Recently, concerns have been raised that vertical wavelength filtering can lead to misinterpretation of other wave-like perturbations, such as inertial instability effects, as gravity wave perturbations. In this paper we assess the ability of different spectral background removal approaches to separate gravity waves and inertial instabilities using artificial inertial instability perturbations, global model data and satellite observations. We investigate a horizontal background removal (which applies a zonal wavenumber filter with additional smoothing of the spectral components in meridional and vertical direction), a sophisticated filter based on 2D time–longitude spectral analysis (see Ern et al., 2011) and a vertical wavelength Butterworth filter. Critical thresholds for the vertical wavelength and zonal wavenumber are analysed. Vertical filtering has to cut deep into the gravity wave spectrum in order to remove inertial instability remnants from the perturbations (down to 6 km cutoff wavelength). Horizontal filtering, however, removes inertial instability remnants in global model data at wavenumbers far lower than the typical gravity wave scales for the case we investigated. Specifically, a cutoff zonal wavenumber of 6 in the stratosphere is sufficient to eliminate inertial instability structures. Furthermore, we show that for infrared limb-sounding satellite profiles it is possible as well to effectively separate perturbations of inertial instabilities from those of gravity waves using a cutoff zonal wavenumber of 6. We generalize the findings of our case study by examining a 1-year time series of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data.

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Section: Introductionmentioning

confidence: 61%

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

et al. 2020

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“…The accuracy of the RO temperature measurements could be broadly documented. In the past, several comparison studies between GPS RO data and radiosondes as well as cross validations with other satellite sensors have been performed [ Hajj et al , 2004; Kuo et al , 2005; Steiner et al , 2007; Gobiet et al , 2007; Schmidt et al , 2008; Heise et al , 2008]. Special comparisons of tropopause parameters between CHAMP and ECMWF (European Centre for Medium‐Range Weather Forecasts) or NCEP (National Centers for Environmental Prediction) analyses are given by, for example, Borsche et al [2007] and Schmidt et al [2004, 2005b].…”

Section: Introductionmentioning

confidence: 99%

Observational characteristics of the tropopause inversion layer derived from CHAMP/GRACE radio occultations and MOZAIC aircraft data

Schmidt

Cammas

Smit³

et al. 2010

J. Geophys. Res.

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[1] In this study we discuss characteristics of the Northern Hemisphere (NH) midlatitude (40°N-60°N) tropopause inversion layer (TIL) based on two data sets. First, temperature measurements from GPS radio occultation data (CHAMP and GRACE) for the time interval 2001-2009 are used to exhibit seasonal properties of the TIL bottom height defined here as the height of the squared buoyancy frequency minimum N 2 below the thermal tropopause, the TIL maximum height as the height of the N 2 maximum above the tropopause, and the TIL top height as the height of the temperature maximum above the tropopause. Mean values of the TIL bottom, TIL maximum, and TIL top heights relative to the thermal tropopause for the NH midlatitudes are (−2.08 ± 0.35) km, (0.52 ± 0.10) km and (2.10 ± 0.23) km, respectively. A seasonal cycle of the TIL bottom and TIL top height is observed with values closer to the thermal tropopause during summer. Secondly, high-resolution temperature and trace gas profile measurements on board commercial aircrafts (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program) from 2001-2008 for the NH midlatitude (40°N-60°N) region are used to characterize the TIL as a mixing layer around the tropopause. Mean TIL bottom, TIL maximum, and TIL top heights based on the MOZAIC temperature (N 2 ) measurements confirm the results from the GPS data, even though most of the MOZAIC profiles used here are available under cyclonic situations. Further, we demonstrate that the mixing ratio gradients of ozone (O 3 ) and carbon monoxide (CO) are suitable parameters for characterizing the TIL structure.

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“…Both AIRS retrievals—infrared‐only and combined infrared and microwave—contain a large error in the annual cycle of temperature poleward of 60°S in the stratosphere, alternating in sign approximately every scale‐height. The error is ≈3 K. Such behavior has been observed in comparisons of GPS RO temperature climatologies with atmospheric analyses that are strongly informed by nadir radiance data (Bormann & Healy, ; Foelsche et al, ; Gobiet et al, ; Schmidt et al, ). The error could not be discerned in the radiance data itself, and thus it was identified as a null‐space error in the atmospheric analyses.…”

Section: Conclusion and Discussionmentioning

confidence: 61%

Temperature Trends and Anomalies in Modern Satellite Data: Infrared Sounding and GPS Radio Occultation

Leroy

Verkhoglyadova

2018

JGR Atmospheres

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Trends in monthly average, zonal average temperature in the stratosphere as retrieved from highly accurate modern satellite data are intercompared and compared with climate reanalyses from 2003 through 2014. The data sets used are those of Atmospheric Infrared Sounder and Global Positioning System (GPS) radio occultation, and the reanalyses are those of MERRA and ERA-Interim. Trends produced by all data sets agree to within 0.02 K/year in the lower stratosphere and 0.05 K/year in the middle stratosphere. A number of retrieval errors are found that introduce incorrect trends and seasonal anomalies. Adding microwave data to the infrared retrieval changes trends by approximately 0.01 K/year, thus improving agreement with the other data sets. The signature of the quasi-biennial oscillation in temperature and the annual cycle of temperature over Antarctica as retrieved from infrared data contain null-space errors of more than 3 K due to erroneous priors used in retrieval. Nonuniformity in GPS radio occultation gives rise to errors because changes in received GPS signal strength alter the upper boundary initialization in radio occultation retrieval. Finally, an incorrect specification of atmospheric water vapor introduces an erroneous seasonal cycle of temperature as retrieved from GPS radio occultation data in the upper troposphere. All of these time-dependent retrieval errors can be corrected with future research and improvements to spectral infrared and GPS radio occultation retrieval systems.Plain Language Summary Satellite instruments that have been observing the atmosphere since 2003 are highly calibrated and particularly rich in information. Two of them have been measuring temperature trends in the atmosphere between 7 and 30 km altitude, and their results differ by an uncomfortable amount. Because the measurement techniques have nothing in common, it is possible to trace the causes of the differences to fairly well-known problems in their formulations that translate basic measurements to air temperature. The results of this paper will direct those responsible for retrieving temperature from modern satellite data to fix these problems and thereby bring multiple, independent observations of temperature trends into better agreement with each other.

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Comparison of ECMWF analyses with GPS radio occultations from CHAMP

Abstract: Abstract.A climatological validation of the 6-hourly operational ECMWF troposphere and lower stratosphere temperatures as well as geopotential heights between 1000 and 10 hPa is performed using the

Cited by 12 publications

References 26 publications

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

Removing spurious inertial instability signals from gravity wave temperature perturbations using spectral filtering methods

Observational characteristics of the tropopause inversion layer derived from CHAMP/GRACE radio occultations and MOZAIC aircraft data

Temperature Trends and Anomalies in Modern Satellite Data: Infrared Sounding and GPS Radio Occultation

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