Náttúrufræðingurinn - 1998, Page 48

■ ÞAKKIR
Reikningamir sem hér hefur verið greint frá
voru framkvæmdir hjá Centre National de
Recherches Météorologiques í Toulouse í
Frakklandi með styrk frá Rannsóknarráði
íslands. Veðurfræðingunum Einari Svein-
björnssyni og Eyjólfi Þorbjörnssyni er
þakkað fyrir að hafa vakið athygli höfundar
á óveðrinu og Einari Sveinbjörnssyni,
Lúðvík E. Gústafssyni og Þórönnu Páls-
dóttur fyrir yfirlestur handrits. Veðurathug-
anir sem greint er frá eru fengnar á Veður-
stofu Islands. Auk þeirra er stuðst við lýs-
ingu Sæmundar Runólfssonar á óveðrinu í
Mosfellsbæ.
■ HEIMILDIR
Bougeault, P. & P. Lacarrére 1989. Para-
meterization of Orography-Induced Turbu-
lence in a Mesobeta-Scale model. Mon. Wea.
Rev. 117. 1872-1890.
Gal-Chen, T. & R.C.J. Sommerville 1975. On
the Use of a Coordinate Transformation for
the Solution of the Navier-Stokes Equations.
J. Comput. Phys. 17. 209-228.
Haraldur Ólafsson 1996. Atlas des écoulements
hydrostatiques autour d’un relief idéalisé. 1.
rit Rannsóknastofu í veðurfræði og 42. rit
CNRM. Fáanlegt hjá höfundi.
Haraldur Ólafsson 1997a. Hefur orsök vinds
áhrif á hversu gott skjól myndast af skógi?
Skógræktarritið, Arsrit Skógræktarfélags
íslands 1997. 97-103.
Haraldur Ólafsson 1997b. Hvers vegna hvessti í
Kverkfjöllum? Náttúrufræðingurinn 66. 127-
131.
Lipps, F.B. & R.S. Hemler 1982. A scale analy-
sis of deep moist convection and some related
numerical calculations. J. Atmos. Sci. 39.
2192-2210.
■ SUMMARY
LoCAL WINDSAND SHELTER IN THE
VICINITYOF MOUNTAINS ~ThE 14 JULY
1990 WINDSTORM
A high-resolution numerical non-hydrostatic
model (Meso-NH) is used to simulate a local
orographic windstorm in the Reykjavík area, Ice-
land. The model is initialized with a radio-
sounding from Keflavik on 1200 UTC 14 July
1990 and runs with a 1 km mesh in 40 vertical
levels. The lateral boundary conditions come
from the same radiosounding and they are kept
constant during the simulation. Both the
Coriolis force and realistic values of surface fric-
tion are taken into account. The experiment re-
veals a strong corner wind south of the mountain
Esja with maximum wind speeds slightly less
than observed. The corner wind is related to an
orographic blocking by the mountain range ex-
tending from Esja to Botnssúlur and an inversion
at about 800 meters height. The numerical calcu-
lations also reveal several places where the wind
speed is greatly reduced by the complex land-
scape. Wind data from one of these places,
Þingvellir, is compared with the mean wind
speed at 4 surrounding stations, and it turns out
that on the average, the wind speed is much less
at Þingvellir than at the other stations when the
wind is blowing from the southeast. Finally, the
atmospheric conditions that led to the wind-
storm are discussed. These are characterized by
warm and very stable airmass that has traveled
over relatively cold ocean.
PÓST- OG NETFANG HÖFUNDAR/AuTHOr’s
ADDRESS &E-MAIL
Haraldur Ólafsson
Hávallagötu 48
101 Reykjavík
haraldur@vedur.is
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