Observation of strato-mesospheric CO above Kiruna with ground-based microwave radiometry – retrieval and satellite comparison

Abstract

Abstract. CO serves as a tracer for dynamics in the polar winter middle atmosphere. This work presents the retrieval and the characterization of ground-based CO measurements from the winters 2008/2009 and 2009/2010 by the Kiruna microwave radiometer KIMRA, located in northern Sweden (67.8 • N, 20.4 • E). Furthermore, the dataset is used for an extensive comparison to the recent satellite instruments MLS on Aura, ACE-FTS, and MIPAS on Envisat.The vmr profiles are retrieved using the optimal estimation approach. A detailed analysis of the averaging kernel functions is carried out, showing sensitivity of the measurements between 40 and 80 km altitude, a vertical resolution of 16 to 22 km, as well as a residual influence of the region up to 130 km altitude. An error assessment reveals a total error of the retrieved profile that increases with altitude and is approx. ±0.1 ppmv at 50 km altitude and ±3 ppmv at 80 km altitude. The main contributions to this total error arise from the measurement noise and the uncertainty of the used temperature profiles. The expected dynamical features of the polar winter middle atmosphere are qualitatively identified in the retrieved time series, but are not quantitatively analyzed here.The dense MLS dataset is used to investigate the influence of the collocation criteria on the satellite comparison, showing that relaxing the distance criterion causes a high bias for MLS. The comparison including the other instruments is difficult because of the small number of coincidences. However, Correspondence to: C. G. Hoffmann (christoph.hoffmann@iup.physik.unibremen.de) it suggests that there is a general agreement between KIMRA and the satellite instruments below 65 km altitude, but a high bias for KIMRA above this altitude. Furthermore, the shape of the KIMRA profile appears to be systematically different from the satellite profiles.

A compact receiver system for simultaneous measurements of mesospheric CO and O<sub>3</sub>

“…The altitude of the "tertiary ozone peak" is close to the upper limit of MLS O 3 data, which can explain the low bias of MLS winter nighttime O 3 above ≈ 70 km compared to the data presented in this report and to the data set of Palm et al (2010). Similar discrepancies between mesospheric CO measurements from MLS and ground-based instruments, as presented above, have been reported earlier by Forkman et al (2012) using an older receiver system and by Hoffmann et al (2011).…”

“…Kunzi and Carlson (1982), Aellig et al (1995) and Forkman et al (2003Forkman et al ( , 2012 made frequencyswitched observations of CO at 115.3 GHz. de Zafra and Muscari (2004), Hoffmann et al (2011) and Straub et al (2013) used load-switching to observe CO at 230.5 GHz.…”

Ozone profiles above Kiruna from two ground-based radiometers

“…A value of 0.8 is used here as it limits the contribution of a priori information in the retrieved profile and has been used for sev- eral similar ground-based instruments (e.g. Hoffmann et al, 2011;Straub et al, 2010). This cut-off gives a range of approximately 16-54 km.…”

“…KIMRA has an acousto-optical spectrometer (AOS) with a practical bandwidth of 1.27 GHz and 1801 channels giving a resolution of ∼ 0.7 MHz, as well as two Fast Fourier Transform Spectrometers (FFTSs). The narrowband FFTS, installed in 2007, is often centred on a nearby CO line and has been used in retrieving CO between 40 and 80 km (Hoffmann et al, 2011), and the broadband FFTS, installed in 2012, has been used to measure atmospheric spectra in the region of 230 GHz. The data from the AOS are presented here as its time series extends back to 2002 and the spectrometer is the same model as the MIRA 2 spectrometer.…”

Mesospheric CO above Troll station, Antarctica observed by a ground based microwave radiometer

“…Northern Hemisphere at high latitudes and are taking measurements on a regular basis: the radiometer in Onsala, Sweden described in Forkman et al (2012Forkman et al ( ) from 2002Forkman et al ( to 2008; the radiometer in Kiruna, Sweden described in Hoffmann et al (2011Hoffmann et al ( ) since 2008; and the instrument in Thule, Greenland described in Biagio et al (2010), taking measurements every January to March since 2009. The CO measurements of the instruments in Kiruna and Onsala have been compared to data from Microwave Limb Sounder on the Aura satellite (Aura/MLS) and model output from Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM) and to data of several satellites (Hoffmann et al, 2012;Forkman et al, 2012).…”