Measurements of aerosol optical depth, columnar water vapor and ozone column density were derived by means of a Sun-photometer network (presently 6 stations) in Switzerland. Data are presented until January 2000 of recordings dating back to January 1991. Aerosol optical depths measured at different altitudes were used to characterize tropospheric and stratospheric aerosols. Tropospheric aerosols show a distinct annual course with higher values measured during summer, which is also characteristic for columnar water vapor. An instrument with narrow band channels in the UV provided ozone column density with a high accuracy (1%).

Within the Swiss Atmospheric Radiation Monitoring program (CHARM) the Swiss Meteorological Institute ‐ MeteoSwiss operates a network of presently six Sun photometer stations. Aerosol optical depths (AOD) at 368, 500, and 778 nm were determined from measurements of the relative direct solar irradiance, primarily to provide climatological information relevant in particular to climate change studies. The six instruments are located at various sites representative of high and low altitudes at the north and south part of the Alps in areas free from urban pollution in Switzerland. AOD time series of recordings back to 1991 are discussed, when data were first collected at Davos. An important aerosol layer is often present over stations at lower sites, showing seasonal variability and regional differences for the observed tropospheric aerosols. A classification scheme for synoptic weather types was applied to separate the AOD data into groups corresponding to different atmospheric transport conditions. On average, lower AODs are measured within advective weather situations than within convective ones. However, at the high Alpine sites such a classification is incomplete for AOD characterization due to orographically induced vertical motion. Monthly averaged values of AOD at 500 nm ranged from 0.05 during winter up to 0.3 in summer. The scale height of the aerosol optical depth is found to be 1–2 km depending on season. The high mountain sites are more suitable to the study stratospheric aerosols, for example, the change of the aerosol content and of its size distribution due to Mount Pinatubo eruption was clearly identified at Davos. In 1996 the aerosol optical depth returned to pre‐Pinatubo values. Minimum AODs of ≈0.004–0.007 measured at 500 nm in 1997 are in good agreement with widely reported aerosol optical depth measurements of the stratospheric background aerosols. Besides the Pinatubo‐affected period aerosol characterization by means of the Angström power law exhibits on average a mean wavelength exponent of 1.3–1.8. A climatology of the AOD data obtained between 1994 and 2000 in both space and time has been established.

The present contribution describes the state of implementation of the new Swiss Atmospheric Radiation Monitoring CHARM network to date and the framework for the results already available which were displayed in more details during the IRS-2000 Symposium as separate posters:- Information concerning the long-wave and short-wave irradiance trends at station Payerne since 1993 (B. Goeldi, Poster D24).- Comparisons between simulations and measurements of the direct and diffuse components of the UV effective erythemal irradiances at different altitudes (A. Lehmann, Poster D38).- Measurements at different altitudes with narrow-band spectral radiometers of the aerosol optical depth at three, resp. twelve wavelengths and estimations of the ozone and water vapor columnar amounts (T. Ingold, Poster G99).

Ultraviolet light was measured at four channels (305, 311, 318, and 332 nm) with a precision filter radiometer (UV-PFR) at Arosa, Switzerland (46.78 degrees , 9.68 degrees , 1850 m above sea level), within the instrument trial phase of a cooperative venture of the Swiss Meteorological Institute (MeteoSwiss) and the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center. We retrieved ozone-column density data from these direct relative irradiance measurements by adapting the Dobson standard method for all possible single-difference wavelength pairs and one double-difference pair (305/311 and 305/318) under conditions of cloud-free sky and of thin clouds (cloud optical depth <2.5 at 500 nm). All UV-PFR retrievals exhibited excellent agreement with those of collocated Dobson and Brewer spectrophotometers for data obtained during two months in 1999. Combining the results of the error analysis and the findings of the validation, we propose to retrieve ozone-column density by using the 305/311 single difference pair and the double-difference pair. Furthermore, combining both retrievals by building the ratio of ozone-column density yields information that is relevant to data quality control. Estimates of the 305/311 pair agree with measurements by the Dobson and Brewer instruments within 1% for both the mean and the standard deviation of the differences. For the double pair these values are in a range up to 1.6%. However, this pair is less sensitive to model errors. The retrieval performance is also consistent with satellite-based data from the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) and the Global Ozone Monitoring Experiment instrument (GOME).

In the fall of 1997 the Atmospheric Radiation Measurement program conducted a study of water-vapor-abundance-measurement at its southern Great Plains site. The large number of instruments included four solar radiometers to measure the columnar water vapor (CWV) by measuring solar transmittance in the 0.94-mum water-vapor absorption band. At first, no attempt was made to standardize our procedures to the same radiative transfer model and its underlying water-vapor spectroscopy. In the second round of comparison we used the same line-by-line code (which includes recently corrected H(2)O spectroscopy) to retrieve CWV from all four solar radiometers, thus decreasing the mean CWV by 8-13%. The remaining spread of 8% is an indication of the other-than-model uncertainties involved in the retrieval.

A Sun photometer (18 channels between 300 and 1024 nm) has been used for measuring the columnar content of atmospheric water vapor (CWV) by solar transmittance measurements in absorption bands with channels centered at 719, 817, and 946 nm. The observable is the band‐weighted transmittance function defined by the spectral absorption of water vapor and the spectral features of solar irradiance and system response. The transmittance function is approximated by a three‐parameter model. Its parameters are determined from MODTRAN and LBLRTM simulations or empirical approaches using CWV data of a dual‐channel microwave radiometer (MWR) or a Fourier transform spectrometer (FTS). Data acquired over a 2‐year period during 1996–1998 at two different sites in Switzerland, Bern (560 m above sea level (asl)) and Jungfraujoch (3580 m asl) were compared to MWR, radiosonde (RS), and FTS retrievals. At the low‐altitude station with an average CWV amount of 15 mm the LBLRTM approach (based on recently corrected line intensities) leads to negligible biases at 719 and 946 nm if compared to an average of MWR, RS, and GPS retrievals. However, at 817 nm an overestimate of 2.7 to 4.3 mm (18–29%) remains. At the high‐altitude station with an average CWV amount of 1.4 mm the LBLRTM approaches overestimate the CWV by 1.0, 1.4, and 0.1 mm (58, 76, and 3%) at 719, 817, and 946 nm, compared to the FTS instrument. At the low‐altitude station, CWV estimates, based on empirical approaches, agree with the MWR within 0.4 mm (2.5% of the mean); at the high‐altitude site with a factor of 10 less water vapor the agreement of the SPM with the FTS is 0.0 to 0.2 mm (1 to 9% of the mean CWV there). Sensitivity analyses show that for the conditions met at the two stations with CWV ranging from 0.2 to 30 mm, the retrieval errors are smallest if the 946 nm channel is used.

Over a period of 3 years a precision Sun photometer (SPM) operating between 300 and 1025 nm was calibrated four times at three different high-mountain sites in Switzerland, Germany, and the United States by means of the Langley-plot technique. We found that for atmospheric window wavelengths the total error (2 sigma-statistical plus systematic errors) of the calibration constants V-0 (lambda), the SPM voltage in the absence of any attenuating atmosphere, can be kept below 1.6% in the W-A and blue, 0.9% in the mid-visible, and 0.6% in the near-infrared spectral region. For SPM channels within strong water-vapor or ozone absorption bands a modified Langley-plot technique was used to determine V-0 (lambda) with a lower accuracy. Within the same period of time, we calibrated the SPM five times using irradiance standard lamps in the optical labs of the Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center, Switzerland, and of the Remote Sensing Group of the Optical Sciences Center, University of Arizona, Tucson, Arizona. The lab calibration method requires knowledge of the extraterrestrial spectral irradiance. When we refer the standard lamp results to the World Radiation Center extraterrestrial solar irradiance spectrum, they agree with the Langley results within 2% at 6 of 13 SPM wavelengths. The largest disagreement (4.4%) is found for the channel centered at 610 nm. The results of these intercomparisons change significantly when the lamp results are referred to two different extraterrestrial solar irradiance spectra that have become recently available. (C) 1998 Optical Society of America.

A simple model for the radiometric determination of tropospheric transmittance is based on an isothermal troposphere. In this model the key parameter is the weighted mean tropospheric temperature Tm, which characterizes the radiation and temperature properties of the troposphere. Statistical approaches in modeling this parameter are presented here by using ground temperature, ground relative humidity, and radiometer data. In order to determine the statistical coefficients for Tm modeling and the parameters used in the transmittance retrieval algorithm, radiosonde data were used in a millimeter‐wave propagation model for a site in the Swiss central plane and an Alpine site. Various observing geometries at different millimeter‐wave frequencies were considered. A determination of Tm from ground temperature was achieved with a rms error between 4–5 K for the low‐altitude site and 3–4 K for the high‐altitude site. By incorporating relative humidity or radiometer data, an improvement of up to 25% relative to these values results, depending on frequency and site. The zenith transmittance estimations for the low‐altitude site with our best model have a rms error of 0.5% at 38 GHz, 1% at 94, 110, and 142 GHz, 1.5% at 115 GHz, 2% at 204 GHz, and 3.5% at 279 GHz, whereas for the high‐altitude site all rms errors are below 1%. The inclusion of radiometric information at 20 and 31 GHz did not provide any additional improvement, which was confirmed by actual measurements at 142 GHz.

A characteristic of the politician in perhaps every society is his tendency to talk more, and louder, than other people; and his assumption that these other people the public are interested in what he has to say. The cynic may place the politician's performance in the category of animal noises: barks and threats. The pseudo-cynic credits the politician with a strategic sense, but the 'spoils' turn out to be no more than 'desirable power positions'.2 The politician himself may well claim that his aim is to work towards the realization of his manifesto; and that although a strategic element is involved in reaching a position from which he has the power to implement his ideas, his job is principally to convince the public, and even his opponents, that his manifesto is morally justifiable. These three contrasting views of the business of politics correspond with Rapoport's distinction of 'Fights, Games and Debates'.3 The career of a politician may indeed embrace all these three approaches, and there is little point in trying to argue a case for the priority of one or the other. Whether a politician is driven by private ambition or moral fervour is a matter for his own conscience. However, the analysis of political debate appears to be a grossly neglected topic, whereas the game approach has been rather fashionable recently. In this paper I am concerned with those political middlemen who link 'the public' on the local community level with the higher echelons of the political system. My thesis is that the role of the political middleman encompasses two contrasting but complementary aspects, which I term the entrepreneur4 and the protagonist. The entrepreneurial aspect involves the purely strategic, game-like element, and the protagonist aspect the debate-like element of the middleman's career. The distinction is analytic; empirically the two aspects are mutually supporting and very hard to disentangle. However, consideration of both, rather than the strategic aspect alone, can allow a fuller and perhaps less cynical appreciation of a political career. I shall first sketch a theoretical framework in which the protagonist problem can be handled, and then go on to give a particular case-study, derived from my fieldwork in Finnish Lapland.