Abstract
Abstract. In this analysis, Tropospheric Emission Spectrometer (TES) V004 nadir ozone (O3) profiles are validated with more than 4400 coinciding ozonesonde measurements taken across the world from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) during the period 2005–2010. The TES observation operator was applied to the sonde data to ensure a consistent comparison between TES and ozonesonde data, i.e. without the influence of the a priori O3 profile needed to regulate the retrieval. Generally, TES V004 O3 retrievals are biased high by 2–7 ppbv (7–15%) in the troposphere, consistent with validation results from earlier studies. Because of two degrees of freedom for signal in the troposphere, we can distinguish between upper and lower troposphere mean biases, respectively ranging from −0.4 to +13.3 ppbv for the upper troposphere and +3.9 to +6.0 ppbv for the lower troposphere. Focusing on the 464 hPa retrieval level, broadly representative of the free tropospheric O3, we find differences in the TES biases for the tropics (+3 ppbv, +7%), sub-tropics (+5 ppbv, +11%), and northern (+7 ppbv, +13%) and southern mid-latitudes (+4 ppbv, +10%). The relatively long-term record (6 yr) of TES–ozonesonde comparisons allowed us to quantify temporal variations in TES biases at 464 hPa. We find that there are no discernable biases in each of these latitudinal bands; temporal variations in the bias are typically within the uncertainty of the difference between TES and ozonesondes. Establishing these bias patterns is important in order to make meaningful use of TES O3 data in applications such as model evaluation, trend analysis, or data assimilation.
Highlights
Tropospheric ozone retrieval from Tropospheric Emission Spectrometer (TES)TES is an infrared Fourier transform spectrometer (Beer et al, 2001; Beer, 2006) on-board the NASA Earth Observing System Aura (EOS-Aura) platform
4–6 degrees of freedom (DOFs) for signal, including 1–2 in for signal in the troposphere, we can distinguish between up- the troposphere as compared to 0.5 to 1 DOF for UV/VIS
Tropospheric Emission Spectrometer (TES) V004 nadir O3 profiles were validated with more than 4400 coinciding ozonesonde measurements taken across the world and during the period 2005–2010
Summary
TES is an infrared Fourier transform spectrometer (Beer et al, 2001; Beer, 2006) on-board the NASA Earth Observing System Aura (EOS-Aura) platform. TES retrievals (described in detail by Bowman et al, 2006; Clough et al, 2006; Kulawik et al, 2006a) are based on iteratively fitting of radiative transfer forward model simulations – which relates the atmospheric state to radiance values using atmospheric temperature and constituent profiles as well as the surface properties – to observed radiances at the TES sensor. Reprocessing the TES profiles using a universal a priori is based on the method described in Zhang et al (2006) by adding to the original O3 1 retrievals the difference of both (MOZART 10◦ × 60◦ and MOZART global mean) a priori profiles multiplied by the 3 difference of the unity and averaging kernel matrix. In 7 contrast, O3 concentrations are high over and downwind of 8 polluted regions with strong precursor emissions, i.e. NOx, 9 volatile organic compounds (VOCs), ample sunlight, and favourable dynamical conditions such as the Mediterranean, the Middle East, eastern China, and central Africa (e.g. Liu et al, 2009; Worden et al, 2009)
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