Abstract. The motivation of this study is to verify theoretical expectations placed on ground-based microwave radiometer (MWR) techniques and to confirm whether they are suitable for supporting key missions of national weather services, such as timely and accurate weather advisories and warnings. We evaluate reliability and accuracy of atmospheric temperature profiles retrieved continuously by the microwave profiler system HATPRO (Humidity And Temperature PROfiler) operated at the aerological station of Payerne (MeteoSwiss) in the time period August 2006-December 2009. Assessment is performed by comparing temperatures from the radiometer against temperature measurements from a radiosonde accounting for a total of 2107 quality-controlled all-season cases.In the evaluated time period, the MWR delivered reliable temperature profiles in 86 % of all-weather conditions on a temporal resolution of 12-13 min. Random differences between MWR and radiosonde are down to 0.5 K in the lower boundary layer and increase to 1.7 K at 4 km height. The differences observed between MWR and radiosonde in the lower boundary layer are similar to the differences observed between the radiosonde and another in-situ sensor located on a close-by 30 m tower. Temperature retrievals from above 4 km contain less than 5 % of the total information content of the measurements, which makes clear that this technique is mainly suited for continuous observations in the boundary layer. Systematic temperature differences are also observed throughout the retrieved profile and can account for up to ±0.5 K. These errors are due to offsets in the measurements of the microwave radiances that have been corrected for in data post-processing and lead to nearly bias-free overall temperature retrievals. Different reasons for the radiance offsets are discussed, but cannot be unambiguously determined retrospectively. Monitoring and, if necessary, corrections for radiance offsets as well as a real-time rigorous automated data quality control are mandatory for microwave profiler systems that are designated for operational temperature profiling. In the analysis of a subset of different atmospheric situations, it is shown that lifted inversions and data quality during precipitation present the largest challenges for operational MWR temperature profiling.
Abstract. This paper presents results of the extensive field campaign CLACE 2010 (Cloud and Aerosol Characterization Experiment) performed in summer 2010 at the Jungfraujoch (JFJ) and the Kleine Scheidegg (KLS) in the Swiss Alps. The main goal of this campaign was to investigate the vertical variability of aerosol optical properties around the JFJ and to show the consistency of the different employed measurement techniques considering explicitly the effects of relative humidity (RH) on the aerosol light scattering. Various aerosol optical and microphysical parameters were recorded using in-situ and remote sensing techniques. In-situ measurements of aerosol size distribution, light scattering, light absorption and scattering enhancement due to water uptake were performed at the JFJ at 3580 m a.s.l.. A unique set-up allowed remote sensing measurements of aerosol columnar and vertical properties from the KLS located about 1500 m below and within the line of sight to the JFJ (horizontal distance of approx. 4.5 km). In addition, two satellite retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as back trajectory analyses were added to the comparison to account for a wider geographical context. All in-situ and remote sensing measurements were in clear correspondence. The ambient extinction coefficient measured in situ at the JFJ agreed well with the KLSbased LIDAR (Light Detection and Ranging) retrieval at the altitude-level of the JFJ under plausible assumptions on the LIDAR ratio. However, we can show that the quality of this comparison is affected by orographic effects due to the exposed location of the JFJ on a saddle between two mountains and next to a large glacier. The local RH around the JFJ was often higher than in the optical path of the LIDAR measurement, especially when the wind originated from the south via the glacier, leading to orographic clouds which remained lower than the LIDAR beam. Furthermore, the dominance of long-range transported Saharan dust was observed in all measurements for several days, however only for a shorter time period in the in-situ measurements due to the vertical structure of the dust plume. The optical properties of the aerosol column retrieved from SEVIRI and MODIS showed the same magnitude and a similar temporal evolution as the measurements at the KLS and the JFJ. Remaining differences are attributed to the complex terrain and simplifications in the aerosol retrieval scheme in general.
The development of the planetary boundary layer (PBL) has been studied in a complex terrain using various remote sensing and in situ techniques. The high-altitude research station at Jungfraujoch (3,580 m a.s.l.) in the Swiss Alps lies for most of the time in the free troposphere except when it is influenced by the PBL reaching the station, especially during the summer season. A ceilometer and a wind profiler were installed at Kleine Scheidegg, a mountain pass close to Jungfraujoch, located at an altitude of 2,061 m a.s.l. Data from the ceilometer were analyzed using two different algorithms, while the signal-to-noise ratio of the wind profiler was studied to compare the retrieved PBL heights. The retrieved values from the ceilometer and wind profiler agreed well during daytime and cloud-free conditions. The results were additionally compared with the PBL height estimated by the numerical weather prediction model COSMO-2, which showed a clear underestimation of the PBL height for most of the cases but occasionally also a slight overestimation especially around noon, when the PBL showed its maximum extent. Air parcels were transported upwards by slope winds towards Jungfraujoch when the PBL was higher than 2,800 m a.s.l. during cloud-free cases. This was confirmed by the in situ aerosol measurements at Jungfraujoch with a significant increase in particle number concentration, particle light absorption and scattering coefficients when PBL-influenced air masses reached the station in the afternoon hours. The continuous aerosol in situ measurements at Jungfraujoch were clearly influenced by the local PBL development but also by long-range transport phenomena such as Saharan dust or pollution from the south.
Abstract. We reconstruct atmospheric wet refractivity profiles for the western part of Switzerland with a least-squares collocation approach from data sets of (a) zenith path delays that are a byproduct of the GPS (global positioning system) processing, (b) ground meteorological measurements, (c) wet refractivity profiles from radio occultations whose tangent points lie within the study area, and (d) radiosonde measurements. Wet refractivity is a parameter partly describing the propagation of electromagnetic waves and depends on the atmospheric parameters temperature and water vapour pressure. In addition, we have measurements of a lower Vband microwave radiometer at Payerne. It delivers temperature profiles at high temporal resolution, especially in the range from ground to 3000 m a.g.l., though vertical information content decreases with height. The temperature profiles together with the collocated wet refractivity profiles provide near-continuous dew point temperature or relative humidity profiles at Payerne for the study period from 2009 to 2011.In the validation of the humidity profiles, we adopt a twostep procedure. We first investigate the reconstruction quality of the wet refractivity profiles at the location of Payerne by comparing them to wet refractivity profiles computed from radiosonde profiles available for that location. We also assess the individual contributions of the data sets to the reconstruction quality and demonstrate a clear benefit from the data combination. Secondly, the accuracy of the conversion from wet refractivity to dew point temperature and relative humidity profiles with the radiometer temperature profiles is examined, comparing them also to radiosonde profiles.For the least-squares collocation solution combining GPS and ground meteorological measurements, we achieve the following error figures with respect to the radiosonde reference: maximum median offset of relative refractivity error is −16 % and quartiles are 5 % to 40 % for the lower troposphere. We further added 189 radio occultations that met our requirements. They mostly improved the accuracy in the upper troposphere. Maximum median offsets have decreased from 120 % relative error to 44 % at 8 km height. Dew point temperature profiles after the conversion with radiometer temperatures compare to radiosonde profiles as to: absolute dew point temperature errors in the lower troposphere have a maximum median offset of −2 K and maximum quartiles of 4.5 K. For relative humidity, we get a maximum mean offset of 7.3 %, with standard deviations of 12-20 %.The methodology presented allows us to reconstruct humidity profiles at any location where temperature profiles, but no atmospheric humidity measurements other than from GPS are available. Additional data sets of wet refractivity are shown to be easily integrated into the framework and strongly aid the reconstruction. Since the used data sets are all operational and available in near-realtime, we envisage the methodology of this paper to be a tool for nowcasting of clouds and r...
Abstract. The meteorological surveillance of the four nuclear power plants in Switzerland is of first importance in a densely populated area such as the Swiss Plateau. The project "Centrales Nucléaires et Météorologie" CN-MET aimed at providing a new security tool based on one hand on the development of a high resolution numerical weather prediction (NWP) model. The latter is providing essential nowcasting information in case of a radioactive release from a nuclear power plant in Switzerland. On the other hand, the model input over the Swiss Plateau is generated by a dedicated network of surface and upper air observations including remote sensing instruments (wind profilers and temperature/humidity passive microwave radiometers). This network is built upon three main sites ideally located for measuring the inflow/outflow and central conditions of the main wind field in the planetary boundary layer over the Swiss Plateau, as well as a number of surface automatic weather stations (AWS). The network data are assimilated in real-time into the fine grid NWP model using a rapid update cycle of eight runs per day (one forecast every three hours). This high resolution NWP model has replaced the former security tool based on in situ observations (in particular one meteorological mast at each of the power plants) and a local dispersion model. It is used to forecast the dynamics of the atmosphere in the planetary boundary layer (typically the first 4 km above ground layer) and over a time scale of 24 h. This tool provides at any time (e.g. starting at the initial time of a nuclear power plant release) the best picture of the 24-h evolution of the air mass over the Swiss Plateau and furthermore generates the input data (in the form of simulated values substituting in situ obCorrespondence to: B. Calpini (bertrand.calpini@meteoswiss.ch) servations) required for the local dispersion model used at each of the nuclear power plants locations. This paper is presenting the concept and two validation studies as well as the results of an emergency response exercise performed in winter 2009.
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