In this study I applied Spherical Cap Harmonic Analyses, SCHA, with physical regularization (Korte and Holme, 2003) to synthetic series obtained from the Comprehensive model CM4 (Sabaka et al., 2004), at 46 European observatory locations and additionally 11 'virtual observatories' chosen to improve the initial data distribution.
The main purpose was to find an approach for minimising the known drawbacks of SCHA, and to test different effects on the model results, in order to get a tool which allows a better representation of the geomagnetic main field and its secular variation over restricted areas, as Europe is. I also show that an adequate selection of model parameterisation (spherical cap angle, maximal spherical cap harmonics order, number of splines, norms) and a physical regularization allow that model smoothness and misfit are those required by the data themselves.. The misfit of the final model was tested using different criteria: the rms values, the time evolution of the coefficients and the behaviour of the original versus modelled time series at each location. Models computed for different epochs satisfy the proposed validation criteria, underlining the reliability to compute stable models over the whole considered time span.
This study opens a way to describe in detail regional geomagnetic main field and its secular variation.
Keywords: Geomagnetic field, secular variation, regional modelling, spherical cap harmonic analyses, comprehensive models.
The convective available potential energy (CAPE) closure and the moisture closure is implemented on an analytical linearized model for large-scale motions. The model includes cloud-radiation interaction (CRI), gross moist stability and wind-induced surface heat exchange (WISHE). The model is done in an equatorial non-rotating atmosphere and is vertically resolved.
As the gravity waves in non-rotating atmosphere map to Kelvin waves in rotating atmosphere, the modeled modes are fast Kelvin waves that resemble adiabatic modes, convectively coupled Kelvin modes that are damped and move with the observed phase speed of 17 ms–1 and the unstable slow moisture mode. The slow moisture mode owes its propagation speed to WISHE and instability to CRI and gross moist instability. It is thought that it can be related to the easterly waves and perhaps even the Madden-Julian oscillation (MJO).
Keywords: Kelvin waves, moisture mode.
The thermal assumption of the model is based on the convective available potential energy (CAPE) closure, i.e. increased CAPE, represented by decreased midlevel potential temperature, results in increased precipitation. The dynamic assumption of the model is that the vertical heating profile has the shape of the first baroclinic mode, while the vertical dependence of modeled fields is calculated, i.e. the model is vertically resolved. The modeled modes are free Kelvin waves and convectively coupled Kelvin waves. It is shown that the CAPE closure is not sufficient to produce the observed destabilization of the Kelvin mode, but that the dynamical properties of the model give the observed phase speeds.
Keywords: CAPE, Kelvin waves.
Freaque waves is a newly coined term that combines the two common synonymously used terms of rogue and freak waves. Long before the recent sweeping recognition of the existence of freaque waves, stories of encounters with the unexpected and unusually large waves in the ocean have been told and proffered among seafarers throughout the ages.
After being ignored or dismissed for decades, freaque waves have now emerged as an apropos oceanographic research subject. The current literature consists of various conjectured mechanisms aimed at explaining some aspects for the occurrence of freak waves. Examples are: the linear or nonlinear superposition of waves that lead to larger instability and wave heights, and the focusing of wave energy through time and space, through areas of variable surface ocean currents, and through nonlinear systems such as various attributes of the nonlinear Schrodinger equation. These diversified theoretical postulations mainly demonstrate that it is possible to simulate some wave profiles that might resemble the appearance of freaque waves. At the present, however, none of these conjectures can be readily substantiated by measurements or shed new light on how a freak wave can be recognized before its encounter. There is not even an available universal definition for freaque waves beyond the simple rule of thumb of a height greater than twice the significant wave height. Contrary to some claims, freaque waves are presently not predictable.
The following compilation is an attempt to create a chronology of some of the most-well-known or reliably reported freaque wave encounters, along with their respective, relevant, and easily accessible sources. Each case is generally composed of year, date, location, name of the vessel, a brief description of the encounter, and extent of damages if known. While efforts have been made to incorporate all known cases of freaque waves that were witnessed, alleged, or adverted to, clearly no premise of accuracy or completeness can be vouched for here. Additions, corrections, and modifications are sincerely welcome. (Send to Paul.C.Liu@noaa.gov) This chronology lists cases through January 2007, future encounters as well as missed cases, if any, can be added to future updates.