Gerd Hochschild

Retrieval of ozone mixing ratio profiles from ground-based millimeter wave measurements disturbed by standing waves

We present middle-atmospheric ozone mixing ratio profiles obtained from measurements around 142 GHz using the ground-based millimeter wave radiometer (MIRA 1) developed at the Forschungszentrum Karlsruhe. Data were recorded during spring season of 1994 from the summit of Hornisgrinde (1165 m, 48.61°N, 8.20°E), Germany. They were severely disturbed by standing waves caused by reflections in the internal transmission path. The profiles are retrieved by using a new extension of the well-known constrained linear inversion and optimal estimation method, respectively. With this new extension both techniques are capable of fitting the amplitudes and phases of standing waves in the inversion algorithm itself rather than during preprocessing. In the present paper, analysis of the retrieval technique is given, including a short analysis of sources of error. The new retrieval technique proves to be a reliable tool for the inversion of measured spectra disturbed by standing waves.

Joint retrieval of atmospheric constituent profiles from ground‐based millimeterwave measurements: ClO, HNO3, N2O, and O3

The constrained linear inversion technique and the optimal estimation method are applied to joint retrievals of atmospheric constituent profiles from vertical sounding spectra in the millimeterwave range. The algorithms are illustrated on dual profile retrievals of ozone (O 3 ) and chlorine monoxide (ClO) from synthesized spectra and on dual profile retrievals of ozone and chlorine monoxide, of ozone and nitrous oxide (N 2 O), and of ozone and nitric acid (HNO 3 ), respectively, from measurements performed with the ground-based millimeterwave radiometer MIRA II during February and March 1996 at Kiruna. Reconstructed profiles are compared to observations performed by other groups. The joint retrieval concept proves to be a useful tool that provides valuable information about the altitude distribution of atmospheric constituents.

The vertical distribution of ClO at Ny‐Ålesund during March 1997

Results of the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) are compared with vertical ClO profiles measured by the groundbased Millimeter Wave Radiometer MIRA2 inside the vortex during March 1997 at Ny-Alesund. The influence of the OH + ClO and HO 2 + ClO reaction branching ratio and of the absorption cross section of Cl 2 O 2 on the calculated mixing ratios of ClO and ozone has been investigated. In the upper stratosphere the ClO mixing ratio is reduced by 90% by using a minor channel of the OH + ClO reaction with a branching ratio of 0.07. A temperature dependent minor channel of the HO 2 + ClO reaction reduces the upper stratospheric ClO mixing ratio by 22%. Different absorption spectra of Cl 2 O 2 alter the ClO mixing ratios up to 12% at noon at 20 km. This causes differences of 15% in the ozone loss during winter.

Influence of Solar Radiation on the Diurnal and Seasonal Variability of O3 and H2O in the Stratosphere and Lower Mesosphere, Based on Continuous Observations in the Tropics and the High Arctic

During the CAWSES DFG (German Research Association) priority program measurements of stratospheric and mesospheric O3 using ground based millimeterwave radiometry have been established and analyzed. Instruments have been operated at two different locations, at Merida, Venezuela, a high altitude tropic station and at Ny Alesund, Spitsbergen, an Arctic station. Additionally, data obtained from the millimeterwave radiometer based at Kiruna, Sweden, have been used for an analysis of the 5-day planetary wave.

Intercomparison of Odin-SMR ozone profiles with ground-based millimetre wave observations in the Arctic, the mid-latitudes, and the tropics

Intercomparison of Odin-SMR ozone profiles with ground-based millimetre-wave observations in the Arctic, the mid-latitudes, and the tropics

Inner-tropical ozone measurements at the Mérida Atmospheric Research Station (MARS) using ground-based microwave radiometry

Since March 2004 the ground-based 268–280 GHz radiometer MIRA 2 has been in quasi-continuous operation at the inner-tropical Mérida Atmospheric Research Station (MARS) on Pico Espejo (8.58°N, 71.15°W, 4765 m above sea level) in the Venezuelan Andes. Using the optimal estimation method concentration profiles of ozone have been retrieved in the stratosphere and mesosphere. In the middle stratosphere variations of ozone on a time scale of several months were revealed in the resulting time series that probably result from the turnaround of the Brewer–Dobson circulation. In the mesosphere photochemistry plays the most important role for the ozone concentration. Therefore a diurnal cycle is observed in the upper part of the retrieved ozone profiles. The measurements are used to verify model results of ozone in the mesosphere obtained by a photochemistry model, which reproduces the diurnal variation of ozone very well. Also an inter-annual variation of mesospheric ozone during the month of November in 2004–2007 was observed, primarily during the night. As the time series is still too short to clearly distinguish solar or QBO signals, the cause of this inter-annual variation cannot yet be related to one or the other. In November 2006 an unusual decrease of the ozone partial columns above 60 km was measured; the cause of this decrease is also not identified so far.

Middle-atmospheric water vapour profiles above the Zugspitze obtained with a new ground-based 22 GHz spectroradiometer

The authors present first results from the new MIRA 5 microwave spectroradiometer for middle-atmospheric observations of water vapour at 22 GHz. The data have been taken at Environmental Research Station Schneefernerhaus, Zugspitze, Germany (47°N, 11°E, 2650 m a.s.l.) in January 2009. Comparison with Aura/MLS yields good agreement in the lower and middle stratosphere and some systematic deviation at higher altitudes, which is attributed to a simplified retrieval set-up used in this study.

Profiles of stratospheric ClO and O/sub 3/ simultaneously retrieved from millimeter wave radiometry at Ny-Alesund (Svalbard) during March 1997

Ground-based millimeter wave observations of stratospheric trace gases have been carried out by IMK at the NDSC station Ny-/spl Aring/lesund (78.9/spl deg/ N, 11.9/spl deg/ E) during March 1997. This measurement campaign was the authors contribution to the international intercomparison of chlorine monoxide (ClO) radiometers coordinated by IUP, University Bremen, during which 5 individual instruments have been installed at the same site. The radiometer of IMK has been operated continuously from 12 March to 31 March. Within this timespan there were coincident measurements in parallel with 1 or 2 of the other ClO radiometers on a few days, allowing a direct comparison of the measured spectra and the retrieved profiles. For the entire period the location was inside the polar vortex.

Advanced ground-based monitoring of stratospheric trace gas profiles: calibration, data analysis, and results

The 268-280 GHz radiometer MIRA2 was constructed for ground- based monitoring of vertical profiles of minor stratospheric constituents and has been optimized especially for the observation of the extremely weak chlorine monoxide signature at 278 GHz and its diurnal variation. For calibration an adjustable internal load was developed, which provides any required brightness temperature from cryogenic to ambient temperatures, dependent on mechanical adjustment. In comparison to the well established external beam switching method this new technique result in a higher contrast in particular under critical conditions of the troposphere, For inversion of the measured spectra the modified Constrained Linear Inversion and the Optimal Estimation Method were used alternatively. The extensions of these well established methods include the fit of standing waves within the inversion process itself an the joint retrieval of several spectral lines. The advances in calibration and inversion techniques became obvious during the evaluation of the data measured at Kiruna, Sweden, 1996 and 1998, and Ny-Alesund, Svalbard, 1997. Profiles of the trace gases Ozone, N2O, HNO3 and ClO could be retrieved. From the data measured in Ny-Alesund a unique time series of ClO- and Ozone has been achieved which shows diurnal and long term variations of ClO and Ozone, respectively.

Profiles of stratospheric trace gases retrieved from ground-based millimeter wave radiometry at Ny-/spl Aring/lesund 1997 and Kiruna 1998

During two subsequent polar winter measurement campaigns the ground-based mm wave radiometer MIRA2 has been operated from 12 March to 31 March 1997 at Ny-/spl Aring/lesund (78.9/spl deg/N, 11.9/spl deg/E), Svalbard, and from 26 January to 3 April 1998 at Kiruna (67.8/spl deg/N, 20.4/spl deg/E), Sweden. From the measurements at Ny-/spl Aring/lesund a nearly continuous time series of 100 ClO vmr profiles could be retrieved and compared to calculations of the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA). During the measurement campaign at Kiruna 1998 the weather conditions were not always favorable for ClO measurements. During the periods of bad weather conditions the radiometer was tuned for the detection of ozone resulting in a time series starting from 26 January to 31 March, or for the detection of N/sub 2/O.