placeholder
and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
Language
Year
  • 1
    Language: English
    In: Monthly weather review, 2019-03-01, Vol.147 (3), p.987-1006
    Description: A Bayesian precipitation nowcasting system based on the ensemble Kalman filter is formulated. Starting from the last available radar observations, the prediction step of the filter consists of a stochastic radar extrapolation technique, while the correction step updates the radar extrapolation nowcast using information from the most recent forecast by the numerical weather prediction model (NWP). The result is a flow-dependent and seamless blending scheme that is based on the spread of the nowcast and NWP ensembles, used as the definition of the forecast error. To simplify the matrix operations, the Bayesian update is performed in the subspace spanned by the principal components, hence the term reduced space. Synthetic data experiments demonstrated that the Bayesian nowcast correctly captures the flow dependency in both the NWP forecast and the radar extrapolation skills. Four experiments with real precipitation data and a relatively small ensemble size (21 members) represented a first test under realistic conditions, such as stratiform wintertime precipitation and localized summertime convection. The skill was quantified in terms of fractions skill score at 32-km scale and 2.0 mm h(-1) intensity. The results indicate that the system is able to produce blended forecasts that are at least as skillful as the nowcast-only or the NWP-only forecasts at any lead time.
    Subject(s): Meteorology & Atmospheric Sciences ; Physical Sciences ; Science & Technology
    ISSN: 0027-0644
    E-ISSN: 1520-0493
    Source: Academic Search Ultimate
    Source: Web of Science - Science Citation Index Expanded - 2019〈img src="http://exlibris-pub.s3.amazonaws.com/fromwos-v2.jpg" /〉
    Source: Alma/SFX Local Collection
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Monthly weather review, 2020-06-01, Vol.148 (6), p.2391-2410
    Description: Abstract Currently, major efforts are under way to refine the horizontal resolution of weather and climate models to kilometer-scale grid spacing (Δx). Besides refining the representation of the atmospheric dynamics and enabling the use of explicit convection, this will also provide higher resolution in the representation of orography. This study investigates the influence of these resolution increments on the simulation of orographic moist convection. Nine days of fair-weather thermally driven flow over the Alps are analyzed. Two sets of simulations with the COSMO model are compared, each consisting of three runs at Δx of 4.4, 2.2, and 1.1 km: one set using a fixed representation of orography at a resolution of 8.8 km, and one with varying representation at the resolution of the computational mesh. The spatial distribution of precipitation during daytime is only marginally affected by the orographic details, but nighttime convection to the south of the Alps—triggered by cold-air outflow from the valleys—is very sensitive to orography and precipitation is enhanced if more detailed orography is provided. During daytime, the onset of precipitation is delayed. The amplitude of the diurnal cycle of precipitation is reduced, even though more moisture converges toward the Alpine region during the afternoon. The hereby accumulated moisture sustains precipitation during the evening and nighttime over the surrounding plains. For these differences, the effects of changes in orographic detail are more important than changes in grid spacing. In addition, the individual convective cells are weaker, but their number increases with higher resolved orography.
    ISSN: 0027-0644
    E-ISSN: 1520-0493
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: Monthly weather review, 2010, Vol.138 (9), p.3683-3689
    Description: Abstract Most atmospheric models use terrain-following coordinates, and it is well known that the associated deformation of the computational mesh leads to numerical inaccuracies. In a previous study, the authors proposed a new terrain-following coordinate formulation [the smooth level vertical (SLEVE) coordinate], which yields smooth vertical coordinate levels at mid and upper levels and thereby considerably reduces numerical errors in the simulation of flow past complex topography. In the current paper, a generalization of the SLEVE coordinate is presented by using a modified vertical decay of the topographic signature with height. The new formulation enables an almost uniform thickness of the lowermost computational layers, while preserving the fast transition to smooth levels in the mid and upper atmosphere. This allows for a more consistent and more stable coupling with planetary boundary layer schemes, while retaining the advantages over classic sigma coordinates at upper levels. The generalized SLEVE coordinate is implemented and successfully tested in real-case simulations using an operational nonhydrostatic atmospheric model.
    Subject(s): Convection, turbulence, diffusion. Boundary layer structure and dynamics ; Earth, ocean, space ; Exact sciences and technology ; External geophysics ; Meteorology
    ISSN: 0027-0644
    E-ISSN: 1520-0493
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Atmospheric science letters, 2016-05, Vol.17 (5), p.315-325
    Description: Hail is the costliest atmospheric hazard in Switzerland, causing substantial damage to agriculture, cars and buildings every year. In this study, a 12‐year statistic of objectively identified cold fronts and a radar‐based hail statistic are combined to investigate the co‐occurrence of cold fronts and hail in Switzerland. In a first step, an automated front identification scheme, which has previously been designed for and applied to global reanalysis data, is modified for a high‐resolution regional analysis data set. This front detection method is then adapted, tested and applied to the Consortium for Small Scale Modelling (COSMO) analysis data for the extended hail season (May to September) in the years 2002–2013. The resulting cold front statistic is presented and discussed. In a second step, the frequency of cold fronts is linked to a high‐resolution radar‐based hail statistic to determine the relative fraction of hail initiation events in pre‐frontal environments. Up to 45% of all detected hail events in north‐eastern and southern Switzerland form in pre‐frontal zones. Similar fractions are identified upstream of the Jura and the Black Forest mountains. The percentage of front‐related hail formation is highest in regions where hail is statistically less frequent, with the exception of southern Switzerland. Furthermore, it is shown that fronts create wind‐sheared environments, which are favourable for hail cells.
    Subject(s): climatology ; front ; hail ; high impact weather ; severe weather ; thunderstorm
    ISSN: 1530-261X
    E-ISSN: 1530-261X
    Source: DOAJ Directory of Open Access Journals - Not for CDI Discovery
    Source: ProQuest Central
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Quarterly journal of the Royal Meteorological Society, 2018-04, Vol.144 (713), p.1218-1256
    Description: Data assimilation (DA) methods for convective‐scale numerical weather prediction at operational centres are surveyed. The operational methods include variational methods (3D‐Var and 4D‐Var), ensemble methods (LETKF) and hybrids between variational and ensemble methods (3DEnVar and 4DEnVar). At several operational centres, other assimilation algorithms, like latent heat nudging, are additionally applied to improve the model initial state, with emphasis on convective scales. It is demonstrated that the quality of forecasts based on initial data from convective‐scale DA is significantly better than the quality of forecasts from simple downscaling of larger‐scale initial data. However, the duration of positive impact depends on the weather situation, the size of the computational domain and the data that are assimilated. Furthermore it is shown that more advanced methods applied at convective scales provide improvements over simpler methods. This motivates continued research and development in convective‐scale DA. Challenges in research and development for improvements of convective‐scale DA are also reviewed and discussed. The difficulty of handling the wide range of spatial and temporal scales makes development of multi‐scale assimilation methods and space–time covariance localization techniques important. Improved utilization of observations is also important. In order to extract more information from existing observing systems of convective‐scale phenomena (e.g. weather radar data and satellite image data), it is necessary to provide improved statistical descriptions of the observation errors associated with these observations. Data assimilation methods for convective‐scale numerical weather prediction at operational centres are surveyed. It is demonstrated that the quality of forecasts based on initial data from convective‐scale data assimilation is significantly better than the quality of forecasts from simple downscaling. Furthermore it is shown that more advanced methods applied at convective scales provide improvements over simpler methods.
    Subject(s): convective‐scale ; data assimilation ; Meteorological stations, Radar ; Methods ; Numerical weather forecasting ; numerical weather prediction ; Surveys ; Weather
    ISSN: 0035-9009
    E-ISSN: 1477-870X
    Source: Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Quarterly journal of the Royal Meteorological Society, 2018-04, Vol.144 (713), p.1279-1296
    Description: Ensemble data assimilation methods such as the ensemble Kalman filter (EnKF) are a key component of probabilistic weather forecasting. They represent the uncertainty in the initial conditions by an ensemble that incorporates information coming from the physical model with the latest observations. High‐resolution numerical weather prediction models run at operational centres are able to resolve nonlinear and non‐Gaussian physical phenomena such as convection. There is therefore a growing need to develop ensemble assimilation algorithms able to deal with non‐Gaussianity while staying computationally feasible. In the present article, we address some of these needs by proposing a new hybrid algorithm based on the ensemble Kalman particle filter. It is fully formulated in ensemble space and uses a deterministic scheme such that it has the ensemble transform Kalman filter (ETKF) instead of the stochastic EnKF as a limiting case. A new criterion for choosing the proportion of particle filter and ETKF updates is also proposed. The new algorithm is implemented in the Consortium for Small‐scale Modeling (COSMO) framework and numerical experiments in a quasi‐operational convective‐scale set‐up are conducted. The results show the feasibility of the new algorithm in practice and indicate the strong potential of such local hybrid methods, in particular for forecasting non‐Gaussian variables such as wind and hourly precipitation. High‐dimensional non‐Gaussian filtering problems, such as those encountered in convective‐scale data assimilation, call for the development of new ensemble data assimilation methods. We propose a new algorithm, the LETKPF, which is a hybrid between the LETKF and the PF. Numerical experiments with COSMO in a set‐up similar to the one used operationally at MeteoSwiss show promising results, in particular for forecasting of non‐Gaussian variables such as wind and precipitation.
    Subject(s): Algorithms ; Analysis ; Assimilation ; Climate models ; Convection ; convective scale ; data assimilation ; ensemble Kalman filter ; Feasibility ; high‐dimensional filtering ; Initial conditions ; Kalman filters ; localization ; Numerical weather forecasting ; particle filter ; Precipitation (Meteorology) ; Weather forecasting
    ISSN: 0035-9009
    E-ISSN: 1477-870X
    E-ISSN: 2331-8422
    Source: Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals
    Source: ProQuest Central
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Bulletin of the American Meteorological Society, 2020-07-01, Vol.101 (7), p.E1036-E1051
    Description: AbstractThe current atmospheric observing systems fail to provide a satisfactory amount of spatially and temporally resolved observations of temperature and humidity in the planetary boundary layer (PBL) despite their potential positive impact on numerical weather prediction (NWP). This is particularly critical for humidity, which exhibits a very high variability in space and time or for the vertical distribution of temperature, determining the atmosphere’s stability. Novel ground-based lidar remote sensing technologies and in situ measurements from unmanned aerial vehicles can fill this observational gap, but operational maturity was so far lacking. Only recently, commercial lidar systems for temperature and humidity profiling in the lower troposphere and automated observations on board of drones have become available. Raman lidar can provide profiles of temperature and humidity with high temporal and vertical resolution in the troposphere. Drones can provide high-quality in situ observations of various meteorological variables with high temporal and vertical resolution, but flights are complicated in high-wind situations, icing conditions, and can be restricted by aviation activity. Both observation systems have shown to considerably improve analyses and forecasts of high-impact weather, such as thunderstorms and fog in an operational, convective-scale NWP framework. The results of this study demonstrate the necessity for and the value of additional, high-frequency PBL observations for NWP and how lidar and drone observations can fill the gap in the current operational observing system.
    ISSN: 0003-0007
    E-ISSN: 1520-0477
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Iberoamericana (Madrid, Spain), 2014-06-01, Vol.6 (23), p.281-300
    ISSN: 1577-3388
    E-ISSN: 2255-520X
    Source: JSTOR Arts & Sciences XI
    Source: DOAJ Directory of Open Access Journals - Not for CDI Discovery
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: English
    In: Monthly weather review, 2002, Vol.130 (10), p.2459-2480
    Description: Most numerical weather prediction models rely on a terrain-following coordinate framework. The computational mesh is thus characterized by inhomogeneities with scales determined by the underlying topography. Such inhomogeneities may affect the truncation error of numerical schemes. In this study, a new class of terrain-following coordinate systems for use in atmospheric prediction models is proposed. Unlike conventional systems, the new smooth level vertical (SLEVE) coordinate yields smooth coordinates at mid- and upper levels. The basic concept of the new coordinate is to employ a scale-dependent vertical decay of underlying terrain features. The decay rate is selected such that small-scale topographic variations decay much faster with height than their large-scale counterparts. This generalization implies a nonlocal coordinate transformation. The new coordinate is tested and compared against standard sigma and hybrid coordinate systems using an idealized advection test. It is demonstrated that the presence of coordinate transformations induces substantial truncation errors. These are critical for grid inhomogeneities with wavelengths smaller than approximately eight grid increments, and may overpower the regular-grid truncation error of the underlying finite-difference approximation. These results are confirmed by a theoretical analysis of the truncation error. In addition, the new coordinate is tested in idealized and real-case numerical experiments using a nonhydrostatic model. The simulations using the new coordinate yield a substantial reduction of small-scale noise in dynamical and thermodynamical model fields. (Author)
    Subject(s): Earth, ocean, space ; Exact sciences and technology ; External geophysics ; Geophysics. Techniques, methods, instrumentation and models ; Meteorology ; Weather analysis and prediction
    ISSN: 0027-0644
    E-ISSN: 1520-0493
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    Description: Hail is the costliest atmospheric hazard in Switzerland, causing substantial damage to agriculture, cars and buildings every year. In this study, a 12-year statistic of objectively identified cold fronts and a radar-based hail statistic are combined to investigate the co-occurrence of cold fronts and hail in Switzerland. In a first step, an automated front identification scheme, which has previously been designed for and applied to global reanalysis data, is modified for a high-resolution regional analysis data set. This front detection method is then adapted, tested and applied to the Consortium for Small Scale Modelling (COSMO) analysis data for the extended hail season (May to September) in the years 2002–2013. The resulting cold front statistic is presented and discussed. In a second step, the frequency of cold fronts is linked to a high-resolution radar-based hail statistic to determine the relative fraction of hail initiation events in pre-frontal environments. Up to 45% of all detected hail events in north-eastern and southern Switzerland form in pre-frontal zones. Similar fractions are identified upstream of the Jura and the Black Forest mountains. The percentage of front-related hail formation is highest in regions where hail is statistically less frequent, with the exception of southern Switzerland. Furthermore, it is shown that fronts create wind-sheared environments, which are favourable for hail cells. publishedVersion
    Subject(s): Climatology ; front ; hail ; high impact weather ; severe weather ; thunderstorm
    ISSN: 1530-261X
    E-ISSN: 1530-261X
    Source: Bergen Open Research Archive (BORA)
    Source: DOAJ Directory of Open Access Journals - Not for CDI Discovery
    Source: ProQuest Central
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...