The need for the mariner to have better weather indicators for efficient
ship routeing in the middle latitudes is demonstrated. The benefits of an
early appreciation of the subtle changes in storm behaviour is shown in a
case study. Monitoring of ship's performance through a frontal depression
using a modified Tropical Storm Avoidance simulation, also developed by the
author, shows the penalties of not minimising the effects of wind and waves.
To accomplish the aims of this project diagnostic models are developed,
firstly to show the overall movement of the frontal depression within the
trough - ridge system and secondly to investigate the field structure
appertaining to depression movement and development.
The graphical diagnostic model, an animated movie loop, allows the detail
from two levels to be combined, surface fronts superimposed on the 500 mb
flow, and played back in sequence showing the sophisticated nature of storm
movement. This insight naturally lead to the development of a numerical
diagnostic model to study simple elements such as wind fields. Analysis of
these data enabled a movement indicator for the frontal depression, the "TEN"
Indicator, to be formulated and is based on the 500 mb contours. Further
improvements in the diagnostic numerical model allows the gradients of
synthesised elements to be calculated without the loss of boundary values,
and uses a cubic spline technique based on the Lagrange Interpolation.
Error analysis of the calculated wind fields is carried out to test the
accuracy of the methods employed. The model is then used to analyse a number
of depressions using various development techniques to test the model. The
results from four occasions, of the many observed, are demonstrated showing
the development ideas of Sutcliffe, Petterssen and the Q-Vector based on
quasi-geostrophic theory. Divergence is also considered using gradient wind
substitutions, adjusted for surface friction and modified to satisfy
curvature effects in ridge systems. The four occasions illustrated
demonstrates the similarities between each method, the location of vertical
motion within a deepening depression is located slightly in advance of the
warm front. The normalising of these vertical field indicators against the
surrounding flow allows the visual and numerical appreciation of ascent in
weak fields. This approach may be an advantage in further studies of
cyclogenesis.
The model wind fields are tested using operational wind data, both being
calculated from the same digitised pressure fields. The Oceanroutes
Operational Routeing Model is employed, using these data, to produce two
routes using both the analysis and forecast data. The case study
demonstrates the usefulness of the "TEN" Movement Indicator as it provides
the mariner with the tools to examine depression movement, to check
forecasts and to give him the confidence to question routeing orders. This
method requires data for the surface and the 500 mb level. Recommendations
are suggested to modify the surface weather chart format for the mariner by
including both movement and development information which would economise
and optimise weather data transmission for greater shipboard efficiency.Plymouth Weather Centre,
Meteorological Office,
Plymout