KARE (Kiruna Atmospheric Remote-Sensing Ensemble)

Measurement Description: At the Swedish Institute of Space Physics (Institutet för rymdfysik, IRF) in Kiruna (67.8°N, 20.4°E) and nearby Esrange (67.9°N, 21.1°E) a set of complementary atmospheric remote sensing instruments is operated, taking advantage of its location in the northernmost part of Scandinavia. The research performed include different spectroscopic remote sensing methods and radar technology which are described in the following sections.

1. FTIR-Spectrometer (Responsible Scientists:T. Blumenstock and D. Yashkov)
   Since March 1996 an FTIR-spectrometer (FTS) is in operation at IRF Kiruna by the collaboration IRF/IMK/STEL. The instrument is a commercial BRUKER 120-HR with a spectral resolution of 0.002 cm-1 (360 cm max. OPD). Atmospheric absorption spectra are recorded using the sun or the moon as the source of radiation. Measurements require cloudfree view of either sun or moon at an elevation of greater than one to three degrees. At the site, solar (lunar) measurements are not possible for 8 weeks during polar night (polar day). The time resolution is typically 5 min for solar and 20 min for lunar observations. Lunar measurements are possible for up to 10 nights around full moon. Toggling between solar and lunar observation mode requires no major changes in the setup and can be accomplished within 5 minutes. Vertical total column amounts (VTCA) based on VMR profiles are retrieved for ClONO₂, HCl, HNO₃, O₃, HF, NO, NO₂, CH₄, N₂O, CO₂, CFCs, H₂O, and several others. Additionally, significantly enhanced abundance of CLO is observable. The precision relevant to data comparison when assuming use of the same spectroscopic database by the instruments involved in SOLVE: 4% (O₃), 4% (HNO₃), 12 % (NO), 3% (N₂O), 4% (CH₄), and 10% (NO₂).

    

2. DOAS (Responsible Scientists: T. Wagner, C.-F. Enell)
   In cooperation between IUP and IRF, a UV/visible spectrometer system is operated at IRF since December 1996. The system consists of two grating spectrometers covering the visible and near-UV spectral ranges (375-688 nm and 300-402 nm, respectively). Two zenith-looking telescopes with a field of view of ~1 degrees collect scattered sunlight and feed the spectrometers via optical fiber bundles. The detectors, developed at IUP, are based on 1024-pixel Reticon photodiode arrays. The detectors and spectrometers are temperature-stabilized. This is the only optical remote-sensing technique capable of detecting the BrO radical. In addition, ozone, NO₂ and OClO are routinely retrieved. The results presented are total slant column densities and vertical column densities of the measured species. Together with balloon- and satellite-borne observations, the measurements also allow distinction between stratospheric and tropospheric columns of the species. Besides the retrieval of chemical species, the instrument is also useful for cloud studies by analyzing the ratio of the detected light intensity in different wavelength intervals, a so called color index and the oxygen collision complex O₄. The color index can also be used for identification of stratospheric clouds (PSCs).

    

3. mm-Wave Radiometry (Responsible Scientists: U. Raffalski, G. Hochschild)
   The IRF mm-wave radiometer for observations at 204 GHz is expected to be operational during winter/spring 2000. The design and development was performed in cooperation with the IMK Karlsruhe. The IMK radiometer has been successfully operated on a campaign base in Kiruna and Ny-Ålesund, Svalbard, during the recent 3 winters. The instruments consist of a quasi-optical system that focuses the emitted atmospheric radiation on a cryogenically cooled detector. An acousto-optical spectrometer (AOS) provides spectral information from the atmospheric signal. The radiometers are operated in such a way that it can be directed into any azimuth and zenith angle. Vertical profiles of chlorine monoxide (ClO) and ozone cover the altitude range from 18 to 60 km with at least four independent layers from 18 to 60 km altitude. The time resolution for ozone measurements is typically 1 hour or better. Due to tropospheric water vapor ClO observations will need an integration time of a few hours and are restricted to favorable weather conditions. The accuracy for the retrievals are expected to be better than 10% or 0.5 ppmv for ozone and 30% or 0.6 ppbv for ClO.

    

4. MST Radar (Responsible Scientist: P. Chilson)
   The Esrange MST Radar (ESRAD), located about 30 km east of Kiruna (67.9°N, 21.1°E), is operated jointly by the Swedish Institute of Space Physics and the Swedish Space Corporation at Esrange. It is a 52 MHz (VHF) MST class radar that has been in near continuous operation since the middle of 1996. MST radars such as ESRAD use the signals scattered from refractive index variations in the atmosphere. These fluctuations are caused by small-scale layering and by turbulence. They move passively with the displacement of atmospheric gases so that their movement can be used to determine the winds, and the smaller scale velocity perturbations associated with the propagation of waves. ESRAD will provide information relevant to the dynamics of the atmosphere, that is important when studying lee-wave activity and its connection with the production of Polar Stratospheric Clouds (PSC). ESRAD will operate continuously for the duration of the SAGE III validation experiment in an operational mode concentrating on the troposphere and lower stratosphere.