G. Kopp

Intercomparison of general purpose clear sky atmospheric radiative transfer models for the millimeter/submillimeter spectral range

[1] We compare a number of radiative transfer models for atmospheric sounding in the millimeter and submillimeter wavelength range, check their consistency, and investigate their deviations from each other. This intercomparison deals with three different aspects of radiative transfer models: (1) the inherent physics of gaseous absorption lines and how they are modeled, (2) the calculation of absorption coefficients, and (3) the full calculation of radiative transfer for different geometries, i.e., up-looking, down-looking, and limblooking. The correctness and consistency of the implementations are tested by comparing calculations with predefined input such as spectroscopic data, line shape, continuum absorption model, and frequency grid. The absorption coefficients and brightness temperatures calculated by the different models are generally within about 1% of each other. Furthermore, the variability or uncertainty of the model results is estimated if (except for the atmospheric scenario) the input such as spectroscopic data, line shape, and continuum absorption model could be chosen freely. Here the models deviate from each other by about 10% around the center of major absorption lines. The main cause of such discrepancies is the variability of reported spectroscopic data for line absorption and of the continuum absorption model. Further possible causes of discrepancies are different frequency and pressure grids and differences in the corresponding interpolation routines, as well as differences in the line shape functions used, namely a prefactor of (n/n0 )o r (n/n0) 2 of the Van-Vleck-Weisskopf line shape function. Whether or not the discrepancies affect retrieval results remains to be investigated for each application individually.

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.

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.

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.