|
|
Characteristics of convective environment in ALADIN reanalysis
Zacharov, Petr, jr. ; Vokoun, Martin
For the prediction and assessment of the potential for convective cloud formation, various characteristics of the convective environment are used. Values of CAPE, CIN, wind speed, and temperature at several standard levels are available from the ALADIN reanalysis outputs, from which wind shear and vertical temperature gradient can be calculated. Verification allows for point comparison with data from sounding measurements, for example, from Prague, Libuš.
|
|
|
Precipitation by PERUN
Zacharov, Petr, jr. ; Brožková, R. ; Řezáčová, Daniela
Weather reanalyses are a powerful tool for studying historical weather both at individual points and especially over an area. The detailed reanalysis produced by the PERUN project thus makes it possible to reveal various aspects of the atmosphere to a degree that we are unable to achieve with measurements. Since it is still a model approximation, it is of course necessary to detect systematic biases by verification before its use. Climate model runs, on the other hand, can uncover the future evolution of the atmosphere. Since these calculations cannot yet be verified, it is necessary to validate a historical run of the same model and subtract the revealed systematic errors from the future projections. In the PERUN project, both the historical run and two climate runs up to 2100 have been calculated. In this work, we present a basic verification and validation of the precipitation forecasts and an evaluation of the separation of precipitation into stratiform and convective precipitation and, in addition, into\nliquid and solid precipitation.
|
|
|
Evaluation of precipitation totals simulated by the ALADIN/PERUN atmospheric reanalysis at high spatial resolution
Bližňák, Vojtěch ; Zacharov, Petr, jr.
Atmospheric reanalyses represent powerful tools for obtaining information about the state of the atmosphere in history, which is obtained by numerical weather prediction (NWP) models whose predictions may (but may not) be improved through the assimilation of measured data. Significant developments in computer technology have recently enabled to increase their spatial resolution so that even meteorological phenomena of a local nature can be better captured. However, most NWP models compensate this capability by reducing the computational domain, which largely limits the use of these forecasts for the following meteorological, climatological and/or hydrological applications. The newly developed ALADIN/PERUN atmospheric reanalysis provides simulations of various meteorological variables at high spatial (2.3 km) and temporal (1 h) resolution over most of Europe between 1989 and 2020. Due to the high resolution of the reanalysed data, it can be expected that precipitation fields will capture local-scale processes well, and thus reproduce more faithfully, for example, heavy convective precipitation. The presented paper aims to evaluate this capability based on gauge-adjusted radar estimates of precipitation totals during warm parts of the year when strong convective but also stratiform precipitation occurs in Central Europe. The accuracy of the localization and precipitation sums will be evaluated for two different runs of the NWP model. The first one (ALADIN/Reanalysis) involves a complete assimilation of the observed data every 6 hours using a 4D-VAR assimilation scheme. The second (ALADIN/Evaluation Run) uses only the boundary conditions from the ERA-5 global reanalysis and the calculation of the forecasts is not further modified based on measured data. Comparing the two runs will provide us with information about the level of physical description in the NWP model as well as the effect of assimilation on the resulting precipitation fields. In addition, the paper is unique in that it will use detailed fields of 'observed' precipitation totals at high spatial resolution, which conventional rain gauge data cannot offer.\n
|
|
|
Derecho windstorms
Staněk, Miloslav ; Müller, Miloslav (advisor) ; Zacharov, Petr (referee)
Derecho is a widespread windstorm associated with a line of severe convective storms. To be classified as derecho, the windstorm must exhibit wind gusts exceeding 25 m.s-1 on a major axis length more than 400 km, with minimal three wind gusts exceeding 33 m.s-1 . Various mechanisms play a main role in the formation of these widespread windstorms, which interrelate and can together be responsible for the formation of derecho. However, the occurrence of derechos is not only the domain of the USA, but also of Europe, China and South America. Conditions for the formation and development of derechos in Europe are different from those in the USA and their occurence is not concurrently as frequent as in the USA. Warm season derechos in Europe occur at lower instability than derechos in the USA and at higher deep layer wind shear values. In respect of the extent of the damaged area, the cold season derechos in Europe hit larger areas than derechos in the USA. Warm season derechos in Europe are related to the area of the front side of the upper trough and develop ahead of the cold front near the convergence line. Conversely, cold season derechos are related to the significant cold front. One of the most significant warm season windstorms in the Central Europe occurred on 4th July 1929. This event was...
|
|
| |
|
|
The Evaluation of the Heavy Convective Precipitation Forecast
Zacharov, Petr ; Řezáčová, Daniela (advisor) ; Brechler, Josef (referee) ; Pešice, Petr (referee)
The thesis deal with the evaluation of the quantitative convective precipitation forecast and its uncertainty. Five convective events that produced heavy local rainfall in the Czech Republic were studied. The nonhydrostatic local model LM COSMO was run with a horizontal resolution of 2.8 km and an ensemble of 13 forecasts was created by modifying the initial and boundary conditions. Forecasts were verified by gauge-adjusted radar-based rainfalls. Ensemble skill and ensemble spread were determined using the Fractions Skill Score (FSS). The spread represents the differences between the control forecast and the forecasts provided by each ensemble member, while the skill evaluates the difference between the precipitation forecast and radar-based rainfalls. The numerical experiments used the FSS-skill and spread values related to four events to estimate the skill-spread relationship. The relationship was applied to a fifth event to estimate the QPF ensemble skill given the ensemble FSS-spread. A couple of test of FSS computing were performed. The analysis of these events proved, that the application of the new fuzzy verification scores in high resolution QPF is highly advisable. The new scores are more suitable then the traditional verification scores based on the contingency table. In order to asses the...
|
|
|
Lightning activity prediction using a numerical weather prediction model
Uhlířová, Iva ; Popová, Jana (advisor) ; Zacharov, Petr (referee)
Lightning activity is considered a severe meteorological hazard that needs to be studied, monitored as well as predicted. This thesis focuses on the prediction of lightning activity by the Lightning Potential Index (LPI) in the COSMO numerical weather prediction (NWP) model that comprises 1- and 2-moment (1M and 2M, respectively) cloud microphysical schemes. The objective of this thesis is to investigate the correlation between the predicted lightning activity and the detected one (by the European network for lightning detection EUCLID). Events of the years 2018 and 2019 that recorded significant lightning activity over Czechia are considered for the analyses. For the first time over Czech region, the prognostic values of LPI calculated for each event are verified. In particular, the spatio- temporal distribution of the predicted vs. detected lightning activity is evaluated. Both spatial characterizations and diurnal course of detected lightning activity correspond well to the theoretical knowledge. Thus, spatial (horizontal) and temporal approaches are applied to verify the lightning activity prediction. The results of this thesis successfully verify the LPI prognostic values both in space by comparing the LPI values with the proximity of detected lightning flashes, and in time by contrasting the...
|
|
|
Model of error covariances for the assimilation of radar reflectivity into a NWP model
Sedláková, Klára ; Sokol, Zbyněk (advisor) ; Zacharov, Petr (referee)
MODEL OF ERROR COVARIANCES FOR THE ASSIMILATION OF RADAR REFLECTIVITY INTO NWP MODEL Predicting events with a severe convection is not easy due to the small spatial scale and rapid development of this phenomenon. But being able to predict such events is important in view of the dangerous phenomena that accompany these events, such as flash floods, strong winds, hailstorms or atmospheric electricity. Improved forecast can be achieved by more precisely defined initial conditions that enter the model. These data must match the scale of the studied phenomenon. Therefore, radar data is used in this case. Although the NWP model should describe real processes due to the simplifications and approximations the model's behavior does not entirely correspond the reality. Therefore, if we want the model to generate precipitation, we must ensure that the values of the model variables and their relationship are such that the process is started. To find out these relationships, we want to use a covariant model. In this paper, we focused on the correlation analysis of the model variables in the regions of convection between radar reflection, its conversion to the intensity of precipitation and other model variables. The COSMO data with a horizontal resolution of 2.8 km were used, which were describing approximately...
|
|
| |
|
|
Lightning activity prediction using a numerical weather prediction model
Uhlířová, Iva ; Popová, Jana (advisor) ; Zacharov, Petr (referee)
Lightning activity is considered a severe meteorological hazard that needs to be studied, monitored as well as predicted. This thesis focuses on the prediction of lightning activity by the Lightning Potential Index (LPI) in the COSMO numerical weather prediction (NWP) model that comprises 1- and 2-moment (1M and 2M, respectively) cloud microphysical schemes. The objective of this thesis is to investigate the correlation between the predicted lightning activity and the detected one (by the European network for lightning detection EUCLID). Events of the years 2018 and 2019 that recorded significant lightning activity over Czechia are considered for the analyses. For the first time over Czech region, the prognostic values of LPI calculated for each event are verified. In particular, the spatio- temporal distribution of the predicted vs. detected lightning activity is evaluated. Both spatial characterizations and diurnal course of detected lightning activity correspond well to the theoretical knowledge. Thus, spatial (horizontal) and temporal approaches are applied to verify the lightning activity prediction. The results of this thesis successfully verify the LPI prognostic values both in space by comparing the LPI values with the proximity of detected lightning flashes, and in time by contrasting the...
|
guest ::
RSS feed.