3 research outputs found
Intensity-Duration Relation in the Bartlett-Lewis Rectangular Pulse Model
For several hydrological modelling tasks precipitation time series with a high
(sub-daily) resolution are indispensable. This data is, however, not always
available and thus replaced by model data. A canonical class of stochastic
models for sub-daily precipitation is the class of Poisson cluster processes,
e.g. the Bartlett-Lewis rectangular pulse model (BLRPM). The BLRPM has been
shown to be able to well reproduce certain characteristics found in
observations. Our focus is on intensity-duration relationship which are of
particular importance in the context of hydrological modelling. We analyse
several high resolution precipitation time series (5min) from Berlin and
derive empirical intensity-duration relations for several return levels of
intensities (intensity-duration-frequency curves, IDF curves). In a second
step, we investigate to what extend the variants of a BLRPM are able to
reproduce these relations (i.e. the IDF curves) for different situations
(e.g., seasons) and for the various return-levels of intensities. By means of
a sensitivity study with the BLRPM, we investigate to what extend the ability
to reproduce the intensity-duration relationships is related to certain
relations between the model parameters. Such relations are typically useful to
reduce the complexity of the model and thus robustify and facilitate parameter
estimation
Observational evidence for exponential tornado distributions over specific kinetic energy
Observational evidence supports the recent analytical prediction that tornado intensities are exponentially distributed over peak wind speed squared (v 2), or equivalently, Rayleigh-distributed over v. For large USA data samples, exponential tails are found in the tornado intensity distributions over v 2 from about F2 intensity on. Similar results follow for smaller worldwide data samples. For the 1990s data from the USA and Oklahoma, deviations from the Rayleigh distribution for weak tornadoes can be explained by the emergence of a separate, likely non-mesocyclonic tornado mode. These bimodal datasets can be modeled by superposition of two Rayleigh distributions. The change in modal dominance occurs at about the F2 threshold (v ≈ 50 m s−1). In France, likely mainly the mesocyclonic tornado mode has been recorded, while in the UK, only a non-mesocyclonic mode seems to be present