News Article | December 28, 2015
Clear skies and dry ground have seen the Alpine nation end the year 3.4 degrees Celsius above the long-term historical average for December, a climatologist for the Federal Office of Meteorology and Climatology (MeteoSwiss) said on Monday. "There's no doubt about it," Stephan Bader said. "It's the warmest December in our recorded measurements dating back to 1864 - clearly. And it's especially pronounced at higher altitudes." The dry warmth and slopes bereft of snow have hurt resort owners and ski lift operators, who are already contending with Switzerland's strong currency discouraging foreign visitors. MeteoSwiss earlier this month said it expected 2015 to break the annual record for the third time in just a handful of years. Globally, this year will be the warmest on record and 2016 could be even warmer due to the El Niño weather pattern, the World Meteorological Organization said last month. It warned that inaction on climate change could see global average temperatures rise by 6 degrees Celsius or more.
Teuling A.J.,ETH Zurich |
Teuling A.J.,Wageningen University |
Stockli R.,MeteoSwiss |
Seneviratne S.I.,ETH Zurich
International Journal of Climatology | Year: 2011
The increasing availability of gridded, high-resolution, multivariate climatological data sets calls for innovative approaches to visualize inter-variable relations. In this study, we present a methodology, based on properties of common colour schemes, to plot two variables in a single colour map by using a two-dimensional colour legend for both sequential and diverging data. This is especially suited for climate data as the spatial distribution of the relation between different variables is often as important as the distribution of variables individually. Two example applications are given to illustrate the use of the method: one that shows the global distribution of climate based on observed temperature and relative humidity, and the other showing the distribution of recent changes in observed temperature and precipitation over Europe. A flexible and easy-to-implement method is provided to construct different colour legends for sequential and diverging data. © 2010 Royal Meteorological Society.
Philipona R.,MeteoSwiss |
Krauchi A.,ETH Zurich |
Geophysical Research Letters | Year: 2012
Solar shortwave and thermal longwave radiation at the Earth's surface and at the top of the atmosphere is commonly measured at surface stations, from airplanes and from satellites. Here we show radiative flux profiles measured with radiosondes ascending from the Earth's surface to 35km into the stratosphere. During two-hour flights solar shortwave and thermal longwave radiation are measured both downward and upward with four individual sensors. Daytime solar and thermal radiation is compared to nighttime measurements and 24-hour average radiation budget profiles are shown through the atmosphere. However, of even greater importance with regard to climate change are measured upward and downward longwave greenhouse radiation profiles. Their changes with temperature and water vapor enable direct measurement of radiative forcing through the atmosphere. Measurements during two cloud-free nights with different temperature and different water vapor amount, show an almost equal but opposite net longwave radiation change, or water vapor greenhouse forcing, downwards to the surface and upward into space. Radiative flux profiles clearly illustrate the Earth's atmospheric greenhouse effect, and allow important investigations of clouds and other atmospheric constituents and their effects on shortwave reflection, as well as longwave emission towards the surface and into space. © 2012. American Geophysical Union. All Rights Reserved.
Nisi L.,MeteoSwiss |
Nisi L.,University of Bern |
Ambrosetti P.,MeteoSwiss |
Quarterly Journal of the Royal Meteorological Society | Year: 2014
The purpose of the operationally oriented system named the Context and Scale Oriented Thunderstorm Satellite Predictors Development (COALITION) is automatically to detect severe thunderstorms early in their development and consequently help weather forecasters to increase lead times when issuing severe weather warnings. This new object-oriented system integrates data provided by different sources. Data from the Meteosat Second Generation Rapid Scan Service, weather radar and numerical weather prediction, as well as climatology, are utilized by the system. One of its primary purposes is to use all the best operationally available information about convective processes and to integrate it into a heuristic model. Furthermore the orographic forcing, which is often neglected in heuristic nowcasting models, is taken into account and included in the system as an additional convective triggering mechanism. This is particularly important for areas characterized by complex orography like the Alpine region. The COALITION algorithm merges evolving thunderstorm properties with selected predictors. The forecast evolution of the storm is the result of the interaction between convective signatures and surrounding storm environment. Eight different 'object-environment' interactions are analyzed in eight modules, providing ensemble nowcasts of thunderstorm attributes (satellite- and radar-based) for the following 60 min. All ensemble nowcasts are then combined through a weighting and thresholding scheme and the results are summarized into a single graphical map in order to facilitate user interpretation. The COALITION nowcast system has an update frequency of 5 min. The output highlights the cells having a high probability of severe thunderstorm development within the next 30 min. Verification statistics confirm that COALITION is able to nowcast the intensity of developing convective cells with sufficient skill up to a lead time of about 20 min. © 2013 Royal Meteorological Society.
Panziera L.,MeteoSwiss |
Germann U.,MeteoSwiss |
Gabella M.,MeteoSwiss |
Quarterly Journal of the Royal Meteorological Society | Year: 2011
A novel analogue-based heuristic tool for nowcasting orographic precipitation is presented. The system takes advantage of the orographic forcing, which determines a strong relation between mesoscale flows, air mass stability and rainfall patterns. These quantities are used as predictors of precipitation. In particular, past situations with the predictors most similar to those observed at the current time are identified by searching a large historical dataset. Deterministic and probabilistic forecasts are then generated every five minutes as new observations are available, based on the rainfall observed by radar after the analogous situations. The analogue method provides a natural way to incorporate evolution of precipitation into the nowcasting system and to express forecast uncertainty by means of ensembles. A total of 127 days of long-lasting orographic precipitation constitutes the historical dataset in which the analogous situations are searched. The system is developed for the Lago Maggiore region in the southern part of the European Alps. Given the availability of radar data and the presence of a strong orographic forcing, it can be extended to other mountainous regions. An evaluation of the skill of the system shows that the heuristic tool performs better than Eulerian persistence for predictions with lead time larger than one hour, and better than the numerical model COSMO2 for forecasts with lead time up to four hours. © 2011 Royal Meteorological Society.
Rudolph J.V.,University of Colorado at Boulder |
Friedrich K.,University of Colorado at Boulder |
Journal of Applied Meteorology and Climatology | Year: 2011
A 9-yr (2000-08) analysis of precipitation characteristics for the central and western European Alps has been generated from ground-based operational weather radar data provided by the Swiss radar network. The radar-based precipitation analysis focuses on the relationship between synoptic-scale weather patterns and mesoscale precipitation distribution over complex alpine terrain. The analysis divides the Alps into six regions (each approximately 200×200 km2 in size)-one on the northern side, two each on the western and southern sides of the Alps, and one in the Massif Central-representing various orographic aspects and localized climates within the radar coverage area. For each region, estimated precipitation rate derived from radar data is analyzed on a seasonal basis for total daily precipitation and frequency of high-precipitation-rate events. The summer season has the highest total daily precipitation for all regions in the study, whereas median values of daily precipitation in winter are less than one-half of median daily precipitation for summer. For all regions, high-precipitation-rate events occur most frequently in the summer. Daily synoptic-scale weather patterns are associated with total daily precipitation and frequency of high precipitation rate to show that an advective synoptic-scale pattern with southerly midtropospheric flow results in the highest median and 90th-quantile values for total daily precipitation and that a convective synoptic-scale pattern results in elevated frequency of extreme-precipitation-rate events. © 2011 American Meteorological Society.
Atmosphere | Year: 2014
In several cases (e.g., thermal noise, weather echoes,.), the incoming signal to a radar receiver can be assumed to be Rayleigh distributed. When estimating the mean power from the inherently fluctuating Rayleigh signals, it is necessary to average either the echo power intensities or the echo logarithmic levels. Until now, it has been accepted that averaging the echo intensities provides smaller variance values, for the same number of independent samples. This has been known for decades as the implicit consequence of two works that were presented in the open literature. The present note deals with the deriving of analytical expressions of the variance of the two typical estimators of mean values of echo power, based on echo intensities and echo logarithmic levels. The derived expressions explicitly show that the variance associated to an average of the echo intensities is lower than that associated to an average of logarithmic levels. Consequently, it is better to average echo intensities rather than logarithms. With the availability of digital IF receivers, which facilitate the averaging of echo power, the result has a practical value. As a practical example, the variance obtained from two sets of noise samples, is compared with that predicted with the analytical expression derived in this note (Section 3): Tthe measurements and theory show good agreement. © 2014 by the authors.
Mandapaka P.V.,MeteoSwiss |
Germann U.,MeteoSwiss |
Panziera L.,MeteoSwiss |
Weather and Forecasting | Year: 2012
In this study, a Lagrangian radar echo extrapolation scheme (MAPLE) was tested for use in very short-term forecasting of precipitation over a complex orographic region. The high-resolution forecasts from MAPLE for lead times of 5 min-5 h are evaluated against the radar observations for 20 summer rainfall events by employing a series of categorical, continuous, and neighborhood evaluation techniques. The verification results are then compared with those from Eulerian persistence and high-resolution numerical weather prediction model [the Consortium for Small-scale Modeling model (COSMO2)] forecasts. The forecasts from the MAPLE model clearly outperformed Eulerian persistence forecasts for all the lead times, and had better skill compared to COSMO2 up to lead time of 3 h on average. The results also showed that the predictability achieved from the MAPLE model depends on the spatial structure of the precipitation patterns. This study is a first implementation of the MAPLE model over a complex Alpine region. In addition to comprehensive evaluation of precipitation forecast products, some open questions related to the nowcasting of rainfall over a complex terrain are discussed. © 2012 American Meteorological Society.
Craig G.C.,Ludwig Maximilians University of Munich |
Keil C.,Ludwig Maximilians University of Munich |
Quarterly Journal of the Royal Meteorological Society | Year: 2012
Experience from operational trials of assimilation of radar data in kilometre-scale numerical weather prediction models (operating without cumulus parametrization) shows that the positive impact of the radar data on convective precipitation forecasts typically decays within a few hours, although certain cases show much longer impact time-scales. In this work the impact time of radar data assimilation is related to characteristics of the meteorological environment. Three cases of convection over southern Germany with different synoptic conditions are investigated (one case with two data assimilation cut-off times), each with an ensemble of ten forecasts at 2.8 km horizontal resolution based on different initial and boundary conditions from a global forecast ensemble. Control forecasts are compared with forecasts where radar rainfall data are assimilated using latent heat nudging. The impact time of the radar data on total precipitation is quantified, and found to correlate well with a convective time-scale that measures the rate at which convection is responding to changes in large-scale forcing. Short impact times were associated with short convective time-scales that are characteristic of equilibrium convection. In this regime the statistical properties of the convection are constrained by the large-scale forcing, and effects of the radar data are lost within a few hours as the convection rapidly returns to equilibrium. When the convective time-scale was large (non-equilibrium conditions), the impact of the radar data was longer since convective systems were triggered by the latent heat nudging and were able to persist for many hours in the very unstable conditions present in these cases. The impact of the assimilated radar data on the location of precipitation was assessed using the equitable threat score (ETS) and the displacement and amplitude score (DAS). The impact times for these measures were consistently shorter than for total precipitation, but again shortest for the equilibrium conditions. © 2011 Royal Meteorological Society.
Rudolph J.V.,University of Colorado at Boulder |
Friedrich K.,University of Colorado at Boulder |
Journal of Climate | Year: 2012
Projections of twenty-first-century precipitation for seven Swiss river basins are generated by linking highresolution (2 km × 2 km) radar-estimated precipitation observations to a global climate model (GCM) via synoptic weather patterns. The use of synoptic patterns characterizes the effect of changes in large-scale circulation, or dynamic effects, on precipitation. In each basin observed total daily precipitation received during advective synoptic patterns is shown to be dependent on the basin's general topographic aspect. Across all basins convective synoptic patterns follow the same trend in total daily precipitation with cyclonic patterns consistently producing a larger amount of precipitation than anticyclonic patterns. Identification of synoptic patterns from a GCM for the twenty-first century [Community Climate System Model, version 3.0, (CCSM3)] shows increasing frequency of anticyclonic synoptic patterns, decreasing frequency of cyclonic patterns, and constant frequency of advective patterns over Switzerland. When coupled with observed radar-estimated precipitation for each synoptic pattern, the changes in synoptic pattern frequencies result in an approximately 10%- 15%decrease in decadal precipitation over the course of the twenty-first century for seven Swiss river basins. The study results also show an insignificant change in the future (twenty-first century) probability of exceeding the current (2000-08) 95th quantile of total precipitation. The lack of a trend in exceeding the 95th quantile of precipitation in combination with a decreasing trend in total precipitation provides evidence that dynamic effects will not result in increased frequency of heavy precipitation events, but that heavy precipitation will account for a greater proportion of total precipitation in Swiss river basins by the end of the twenty-first century. © 2012 American Meteorological Society.