The use of IASI data to identify systematic errors in the ECMWF forecasts of temperature in the upper stratosphere

Abstract

Abstract. Since data from the Infrared Atmospheric Sounding Interferometer (IASI) became available in 2007, a number of papers have appeared in the literature which have reported relatively large discrepancies between IASI spectra and forward calculations in the centre of the CO 2 Q-branch at 667 cm −1 . In this paper we show that these discrepancies are primarily due to errors in the temperature profiles used in the forward calculations. In particular, we have used forecasts of temperature profiles from the European Centre for MediumRange Weather Forecasts (ECMWF) to demonstrate that, for the case study considered in this paper, these profiles are affected by systematic errors of the order of ≈10 K at the level of the stratopause. To derive the magnitude and the spatial location of the systematic errors in the temperature profile, we have carried out forward/inverse calculations for a number of clear-sky, daytime, IASI tropical soundings over the sea. The forward calculations have been performed using atmospheric state vectors which have been obtained either from the direct inversion of the IASI radiances or from space-time co-located profiles derived from radiosonde observations and from the ECMWF model. To rule out any effect due to the accuracy of the forward model, we have performed the forward calculations using two independent models. The sensitivity of the temperature biases to the variability of the CO 2 profile and to spectroscopy errors has also been studied.

Error budget analysis of SCIAMACHY limb ozone profile retrievals using the SCIATRAN model

“…An uncertainty of 2 % in the ECMWF data is assumed, which is in agreement with 2-5 % difference for altitudes below 60 km between MAE-STRO, NCEP, and ECMWF (Nowlan, 2006;Masiello et al, 2011). An example of the pressure error profile is shown in Fig.…”

“…Temperature uncertainties in the ECMWF data are assumed to be of the order of 1-2 K from comparisons between IASI, NCEP, and ECMWF for altitudes below 35 km (Nowlan, 2006;Masiello et al, 2011;Boccara et al, 2008). In order to evaluate the possible influence of temperature on ozone, temperature has been increased and decreased by a value of 2 K. The relative errors in retrieved ozone due to uncertainties in temperature of ±2 K are shown in Fig.…”

Simultaneous physical retrieval of surface emissivity spectrum and atmospheric parameters from infrared atmospheric sounder interferometer spectral radiances

“…3 for the two surface coverages analyzed in this paper, namely, sea and desert sand. Methodology and validation of the scheme for the atmospheric parameters have been described in many papers [44][45][46][47][48][49][50][51], to which the reader is referred for further details. For brevity, we limit ourselves to the performance of the scheme.…”

All-sky radiative transfer calculations for IASI and IASI-NG: The σ-IASI-as code

“…We can see that no significant differences occur, neither in the channel at 3.9 μm, which is centred in a spectral atmospheric window, nor in that at 7.3 μm, which instead is also sensitive to the structure of upper troposphere and stratosphere. Other minor differences are due to some well-known biases in ECMWF analyses [11], because we do not perform any residuals' minimization [12,13], but simply we compare simulations and observations. Figure 2, instead, shows an example of spectra, computed at IASI-NG resolution, with and without the extinction due to an ice cloud located in the upper troposphere (whose profile in terms of particles concentration is reported on the right).…”