Swiss Meteorological Institute Research Articles

An Archive for Science, State and Nation : Climatological Data Practices in Switzerland, 1860-1914

In the second half of the nineteenth century, most European countries began to finance weather observation networks. As aresult, climatological data practices changed fundamentally. Using the example of Switzerland, this paper examines the political, institutional and methodological dimensions of national data archives. The institutionalization of data collection within the national framework meant, on the one hand, that more observations were systematically made and published. On the other hand, it also meant that the monitoring was connected to state boundaries. However, based on their universalistic conception of science, this did not preclude national institutions from striving for international data standardization. The national framework also shaped the process of transforming weather observations into statistical data. This information formed the basis for national climatographies and thus had anation-building effect. According to the Swiss Meteorological Institute, climate data were practically useful and had great potential for research work. However, the epistemic status of data collection was uncertain, since physical approaches to climatology had gained in importance. The anticipation of scientific and practical potential benefits played acentral role for the continuation of data production. The Swiss case study presented here illustrates that climatology was transformed by the process of nation-building, affecting its institutional structure, spatial references, and epistemology.

Regional ground surface temperature mapping from meteorological data

Evaluating ground surface temperature (GST) is common in applied and general geothermal research. Our main focus here is investigating GST for Switzerland because of its well-known impact on low-enthalpy resources, like borehole heat exchanger (BHE) utilization. Using mainly meteorological data, we determined the present-day GST distribution through different approaches. First, we analyzed the actual GST data from the last 20 years measured at the meteorological stations of the Swiss Meteorological Institute (SMI) by investigating recent climatic history and annual variation behavior. Recent climate change seems to have a higher impact on Alpine regions than on the Alpine Foreland. Next, we determined the GST altitude dependence in the range of 200–1800 m a.s.l., using nonlinear fitting approaches and investigated the relationship between GST and surface exposure. Contrary to previous publications, no universal correlation between GST and surface exposure was found, due to local and rapid changing meteorological conditions. Finally, we used a complete data set to consider meteorologically relevant data like soil moisture, wind speed, and vegetation cover and height. The measured GST was well reproduced for the case of low vegetation, except when covered by snow and for days of subzero surface air temperature (SAT). Other locations like urban areas could not be tested. Due to the complexity of physical interaction and the resulting assessment of large data sets, this approach is not suitable for determining regional GST distribution which we need as an input for BHE modeling. A relationship between GST and SAT was defined based on the data from the meteorological stations. By applying nonlinear approaches, we established three different altitude zones that require individual consideration. By further processing, an existing SAT map was converted into the first GST map of Switzerland. To verify this new map within the range of validity (up to altitudes of 1500 m a.s.l.), GST values extrapolated from boreholes were used as independent data sources. Generally, a fit with a standard deviation of ±1.0 K was achieved, but local deviations of 2 K also occurred. The new GST map of Switzerland provides useful estimates of regional GST, but not for local effects. It represents an important improvement in evaluating geothermal resources and determines regional GST distribution under vegetation and weather conditions typical of central Europe.

Aerosol optical depth measurements by means of a Sun photometer network in Switzerland

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.

Ozone column density determination from direct irradiance measurements in the ultraviolet performed by a four-channel precision filter radiometer

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).

Advanced control strategy of a solar domestic hot water system with a segmented auxiliary heater

This paper describes improvements that can be introduced at both a structural and control level in order to improve the overall efficiency of solar kits for domestic hot water supply. The plant under consideration is a solar domestic hot water system (SDHWS) manufactured in Switzerland. The heat exchanger is a mantle, which surrounds the entire storage tank. One major structural improvement has been designed. It consists of the replacement of one single electrical element as an auxiliary heater by three smaller ones with different lengths. This configuration requires the manipulation of two additional actuators. An advanced control strategy has been developed to handle the resulting complexity and to achieve higher performances. The actuators are the pump driving the fluid in the collector loop and the three electrical elements. A predictive control strategy has been proposed and validated. It requires solving of an optimization problem and implementation of a state estimator. Weather forecasts as well as prediction of the users’ needs in terms of tapped water are required to implement this predictive control strategy. The weather forecasts are provided on-line by the Swiss Meteorological Institute (SMI). The prediction of the users’ needs is updated every day using an extended Kalman filter. Segmentation of the auxiliary heater coupled with a suitable advanced control strategy have led to significant improvements in terms of comfort and energy consumption.

Analysis of rainfall time series with regard to temporal disaggregation for the use in urban hydrology

The temporal resolution of rain data recorded by national weather services is often lower (10-min resolution) than the data needed for rainfall-runoff simulations (1-5 min resolution). However, the time series are sufficiently long for statistical analysis. The goal of the project presented here is to develop a procedure that disaggregates the 10-min rainfall data of the Swiss Meteorological Institute (SMI) to I-min time resolution. The aim is to implement the procedure in a computer program which can be used by practitioners for generating high resolution rainfall time series at a specific location. In a first step the 1-min data and the 10-min data of two rainfall time series in Switzerland (Heiden, Lucerne) were compared to find characteristic patterns and correlations. The position of 1-min peak within the 10-min interval, the ratio of 1-min peak to 10-min intensity as well as the distribution of the 1-min values within the 10-min interval were investigated. The analysis showed that the positions of the 1-min peaks within a 10-min interval were not uniformly distributed. The distribution depended on the temporal trend of the 10-min values. The ratio of 1-min peak to 10-min intensity seemed to tend towards a constant ratio for high intensities. The results for the two series (Heiden and Lucerne) were not significantly different. These first findings are encouraging with regard to developing a disaggregation to 1-min values which satisfy the accuracy needed in urban hydrology.

Analysis of rainfall time series with regard to temporal disaggregation for the use in urban hydrology

The temporal resolution of rain data recorded by national weather services is often lower (10-min resolution) than the data needed for rainfall-runoff simulations (1–5 min resolution). However, the time series are sufficiently long for statistical analysis. The goal of the project presented here is to develop a procedure that disaggregates the 10-min rainfall data of the Swiss Meteorological Institute (SMI) to 1-min time resolution. The aim is to implement the procedure in a computer program which can be used by practitioners for generating high resolution rainfall time series at a specific location. In a first step the 1-min data and the 10-min data of two rainfall time series in Switzerland (Heiden, Lucerne) were compared to find characteristic patterns and correlations. The position of 1-min peak within the 10-min interval, the ratio of 1-min peak to 10-min intensity as well as the distribution of the 1-min values within the 10-min interval were investigated. The analysis showed that the positions of the 1-min peaks within a 10-min interval were not uniformly distributed. The distribution depended on the temporal trend of the 10-min values. The ratio of 1-min peak to 10-min intensity seemed to tend towards a constant ratio for high intensities. The results for the two series (Heiden and Lucerne) were not significantly different. These first findings are encouraging with regard to developing a disaggregation to 1-min values which satisfy the accuracy needed in urban hydrology.

Low-Level Potential Vorticity and Cyclogenesis to the Lee of the Alps

Abstract High-resolution numerical model simulations over the Alpine region are presented that reveal the presence of low-level elongated bands of potential vorticity (PV) downstream of high topography. These PV streamers (or PV banners) occur when the synoptic-scale wind turns into a direction across the Alps. Individual pairs of banners with anomalously positive and negative values of PV can be attributed to flow splitting, either on the scale of the whole of the Alps (primary banners), or on that of individual massifs and peaks of the model topography (secondary banners). The PV bands have amplitudes of up to −2.5 and +5 pvu, a width of 50–150 km, can attain a length of up to 1500 km, and extend in the vertical from the surface up to the 500-hPa level on occasions. The PV banners are associated with zones of enhanced horizontal wind shear. The analysis of daily output from the operational NWP model run of the Swiss Meteorological Institute also demonstrates that such PV streamers are a frequent feature...

Retrieval of optical depth and particle size distribution of tropospheric and stratospheric aerosols by means of Sun photometry

Aerosol optical depth measurements by means of ground-based Sun photometry were made in Bern, Switzerland during two and a half years primarily to provide quantitative corrections for atmospheric effects in remotely sensed data in the visible and near-infrared spectral region. An investigation of the spatial variability of tropospheric aerosol was accomplished in the summer of 1994 in the Swiss Central Plain, a region often covered by a thick aerosol layer. Intercomparisons are made with two Sun photometers operated by the Swiss Meteorological Institute in Payerne (Swiss Central Plain) and Davos (Swiss Alps, 1590 m a.s.l.). By means of an inversion technique, columnar particle size distributions were derived from the aerosol optical depth spectra. Effective radius, columnar surface area, and columnar mass were computed from the inversion results. Most of the spectra measured in Bern exhibit an Angstrom-law dependence. Consequently, the inverted size distributions are very close to power-law distributions. Data collected during a four month calibration campaign in fall 1993 at a high-mountain station in the Swiss Alps (Jungfraujoch, 3580 m) allowed the authors to study optical properties of stratospheric aerosol. The extinction spectra measured have shown to be still strongly influenced by remaining aerosol of the June 1991 volcanic eruptions of Mount Pinatubo. Inverted particle size distributions can be characterized by a broad monodisperse peak with a mode radius around 0.25 /spl mu/m. Both aerosol optical depths and effective radii had not yet returned to pre-eruption values. Comparison of retrieved aerosol optical depth, columnar surface area and mass, with the values derived from lidar observations performed in Garmisch-Partenkirchen, Southern-Germany, yielded good agreement.

A Water Hypsometer Utilizing High-Precision Thermocouples

A boiling-point barometer—commonly called hypsometer—has been developed for use on meteorological radiosondes. In this hypsometer, water is heated electrically, and its boiling temperature is measured with a thermocouple. Once the boiling temperature is known, pressure is determined via the water vapor saturation pressure curve. The pressure range required is 1050–10 hPa, that is, slightly more than two orders of magnitude. In order to achieve an accuracy of 0.05% in pressure (0.5 hPa at 1000 hPa), boiling temperature must be measured to about 0.01 K. This formidable requirement calls for very accurate calibration procedures that are novel in thermocouple thermometry. However, once the thermocouple is calibrated, individual hypsometers utilizing thermocouples made of the same batch of material do not require calibration. For computing pressure from boiling temperature, the Goff-Gratch reference function is suggested; if approximations cannot be avoided, they must be specially selected. When using another liquid (e.g., fluorochlorohydrocarbons) in the hypsometer, the accuracy required for the temperature measurement would be reduced, however, water was chosen because it is environmentally harmless. Apart from the fact that the hypsometer does not require individual calibration, its advantage over other pressure sensors is the fact that a given uncertainty in boiling temperature leads to a practically constant relative pressure error dp/p over the entire pressure range. Consequently, heights computed for the hypsometer sondes are more accurate than those obtained from sondes employing other pressure sensors (e.g., aneroids), as was confirmed in an intercomparison. The hypsometer is operationally used in the SRS radiosonde by the Swiss Meteorological Institute; so far nearly 3500 successful flights have been made.

Long-Term Records of Snow Cover Water Equivalent in the Swiss Alps

The knowledge of the temporary snow-water equivalent storage term (SWE) is an important prerequisite for the assessment of short- and long-term runoff volumes and water quality aspects. Since SWE measurements are frequently not available, this varilable is modelled on the basis of operationally measured meteorological data. For model verification fortnightly measured SWE values are used. The choice of the proper model depends on the aim of the simulation and the input data available: if SWE is the only variable to be modelled and time-series of daily total and new snow depths values are available, then a simple model based on Martinec (1977) employing settling curves for each snowfall event is suggested. If apart from SWE values other variables such as liquid water storage, snow albedo, etc. are to be modelled, and hourly input data are available, the conceptual energy and mass balance approach as presented here is suggested. The following variables, measured in hourly intervals, are used as input: air temperature, precipitation, wind speed, water vapour pressure, global radiation and cloud cover (term readings). This model was originally developed at a research-type station but can now be applied at up to 70 stations of the automatic network (ANETZ) of the Swiss Meteorological Institute (SMI). The modelled values are good estimates of the measured ones in the accumulation as well as in the ablation season.

Investigations of solar radiation detectors using a laboratory test facility for solar radiation meteorological instruments

A laboratory test facility for solar radiation detectors has been built and is in operation at the Aerological Station of the Swiss Meteorological Institute (SAP/SMI). This installation is conceived as a universal test bed for solar radiation exposed meteorological instruments, and consists of a commercially available solar simulator, a laser alignment system, a translation mechanism with instrument mounts, and an adjustable projection mirror. The solar simulator produces a well characterized radiation beam which can be filtered to match the terrestrial or outer space solar spectrum with an irradiance of up to one solar constant (1367 Wm −2). The instrument mounts and a HeNe laser beam provide a precise and easy alignment of the reference and the test instruments in the radiation beam, allowing for incident angles in the range of 15°–75°. The measurement is based on a comparison of the response of an active cavity absolute radiometer PMO6 with the signal of the test instrument. Detailed investigations of the Haenni Solar 111B type heliometer have revealed important irregularities in the sunshine threshold irradiance angular distribution. Measurements performed with and without the protection glass cover prove the exceedingly high threshold values at large declination angles to be a consequence of enhanced reflections due to the incident angle and inhomogeneities in the glass cover. Very satisfactory results have also been obtained on characterization measurements of pyranometers showing the mean values of the responsivity to be within 0.8% of the calibration values measured at the world radiation center (WRC) at Davos.

Recent developments of the Light Climatic Observatory—ozone measuring station of the Swiss Meteorological Institute (LKO) at Arosa

Recent improvements of the instrumentation at the LKO (Light Climatic Observatory—Ozone measuring station of the Swiss Meteorological Institute), which have been carried out by the Swiss Meteorological Institute (SMI) since 1988, are described. These improvements of the station at Arosa (Switzerland) include the construction of a ‘spectrodome’ (cabin for convenient operation of two Dobson spectrophotometers), partial automation of the two Dobson spectrophotometers D15 and D101 operated side by side (automatic data transmission to a PC), the complete automation of instrument D51 to perform Umkehr measurements and the purchase of two Brewer spectrophotometers (Br40 and Br72). On the basis of digital data acquisition, all calculations to get the final results of the total amount of ozone are performed on PC. A data quality concept under current development is described. Its aim is to compare the consistency of the different quasi-simultaneous measurements and to identify possible drifts in the calibration of the instruments at an early stage.

Un exemple de collaboration internationale en hydrologie

Summary Forecasts of the discharge of the Rhine at Basel have been studied in Zurich since 1954. In this programme have cooperated hydro-power companies of Switzerland, Germany and France, French shipping-firms, and the Dutch water management authorities. For the Netherlands the forecast of the summer yield of the Rhine is of great concern, since it is the main resource of fresh water. The studies have resulted in: — since 1955, annual forecasts of the yield from snowmelt for periods of one to eight months beginning with March, and monthly and bi-monthly forecasts in winter — since 1960, forecasts issued 2 to 5 times per week for the next three days, from October to March. The forecast method is the least squares multiple regression, based on the observations of more than 50 years. For the short term forecasts, the significant predictors are discharge and rainfall, eventually the snow cover percentage on the Swiss midland plateau. The largest errors of forecast were encountered in thawing conditions. Meteorological forecasts are provided by the Swiss Meteorological Institute. For the long range forecasts, the alpine snow pack (in practice represented by the cumulative winter precipitations) and the levels of the Swiss lakes play an important role. The forecasts are used by the hydro-power plants in their operation programmes for maintenance planning, and for proper timing of construction work. In the future, the probability graduation of these forecasts will also be introduced in the optimisation of power production according to the methods of operations research.

EARTHQUAKES IN SWITZERLAND

FROM a seismic point of view, Switzerland is part of the Mediterranean or Alpine-Himalayan geosyncline. Thus it experiences more earthquakes than the whole of northern Europe*. According to figures given by Montessus de Ballore, for every 100 earthquakes humanly felt per unit area in Italy, there are 86-1 in Switzerland and only 5-6 in France. Catalogues of Swiss earthquakes date from the sixteenth and seventeenth centuries, and in 1755 Elie Bertrand published his “Relation Chronologique”. After the Viege earthquake of 1855, Otto Volger published a very detailed catalogue showing epicentres. In 1879 the Swiss Seismological Commission began to publish annually lists of earthquakes with intensities, description of effects, and geographical position. This was replaced in 1914 by the Swiss Seismological Service under Prof. E. Wanner, forming part of the Swiss Meteorological Institute at Zurich.