BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Random time series analysis and extreme wave events - Janssen\, P 
 (European Centre for Medium-Range Weather Forecasts (ECMWF))
DTSTART:20140714T090000Z
DTEND:20140714T100000Z
UID:TALK53388@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:While studying the problem of predicting freak waves it was re
 alized that it would be advantageous to introduce a simple measure for suc
 h extreme events. Although it is customary to characterize extremes in ter
 ms of wave height or its maximum it is argued in this paper that wave heig
 ht is an ill-defined quantity in contrast to\, for example\, the envelope 
 of a wave train. Also\, the last measure has physical relevance\, because 
 the square of the envelope is the potential energy of the wave train. The 
 well-known representation of a narrow-band wave train is given in terms of
  an slowly varying envelope function   and a slowly varying frequency $ome
 ga = ?partial phi /partial t$ where $phi$  is the phase of the wave train.
  The key-point is now that the notion of a local frequency and envelope is
  generalized by applying the same definitions also for a wave\ntrain with 
 a broad-banded spectrum. It turns out that this reduction of a complicated
  signal to only two parameters\, namely envelope and frequency\, still pro
 vides useful information on how to characterize extreme events in a time s
 eries. As an example\, for a linear wave train the joint probability distr
 ibution of envelope height and period is obtained\nand is validated agains
 t results from a Monte Carlo simulation. The extension towards the nonline
 ar regime is\, as will be seen\, fairly straightforward.\n
LOCATION:Seminar Room 2\, Newton Institute Gatehouse
END:VEVENT
END:VCALENDAR