Tp. Lane et al., Observations and numerical modelling of mountain waves over the Southern Alps of New Zealand, Q J R METEO, 126(569), 2000, pp. 2765-2788
Citations number
27
Categorie Soggetti
Earth Sciences
Journal title
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
A detailed case study of mountain waves observed over the South Island of N
ew Zealand during the Southern Alps Experiment is presented. The purpose of
the study is to document the waves generated over this region, to explore
the extent to which high-resolution radiosonde data can be used to determin
e gravity-wave parameters, and to estimate the vertical flux of horizontal
momentum produced by flow over the Southern Alps.
Organized wave clouds were observed in a visible satellite image on 20 Octo
ber 1996 and are thought to have been produced by partially trapped lee wav
es. Using background how fields derived from a radiosonde sounding, the the
oretical horizontal wavelength of the partially trapped mode is calculated
and agrees well with that measured from the satellite image.
A technique, called the horizontal projection method, is developed to analy
se radiosonde soundings for mountain waves. Specifically, the technique det
ermines the dominant horizontal wavelength over the entire depth of a radio
sonde sounding. This method uses a coordinate transformation to take accoun
t of vertical changes in the background flow and, hence, vertical variation
s in the vertical wave number, as well as changes in the path of the radios
onde. This method is applied to a radiosonde sounding to identify the domin
ant wave mode, and emphasizes that radiosonde soundings should not, in gene
ral, be treated as instantaneous vertical profiles when analysing mountain
waves.
The mountain waves observed are simulated using a high-resolution numerical
model and the results are used to check the consistency of the analysis. T
he numerical model produces a horizontally averaged value of momentum flux
in the lower stratosphere of -0.02 N m(-2) although this value is probably
underestimated by at least a factor of four.