Terrain and Precipitation Patterns on Southern Side of the Alps

in Meso-Beta Scale

Jože Rakovec†, Tomaž Vrhovec†, Saša Gaberšek† and Gregor Gregori膇

 

† University of Ljubljana, Ljubljana, Slovenia‡ Present affiliation: Meteorological Office,

EARS, Ljubljana, Slovenia

climatology of Alpine precipitation by Schwarb, Daly, Frei and Schär

flow deflection due to rotational effectsexplains the

secondary Alpine precipitation maximum in Ticino

full lines: displacements thin lines: displacements

Buzzi and Tibaldi 1977Ro=0.7

Schär and Schneidereit 2000

Ro 0.75

Rotunno and Ferretti 2001(the 1994 case) deflection & gradient of potential stability

Rotunno and Ferretti 2001(the 1994 case) deflection & gradient of potential stability

what causes the small scale patches – e.g. the belt of small spots

from Monti Lessini to Karnic Alps?

which is the reasonfor the primary Alpine maximum

in Karnic & Julian Alps?

what causesthe dry area

in Trentino & Tyrol?

what can we learnfrom the simpliest

kinematic simulation?this si not precipitation field!

it is terrain induced vertical velocity in the

mass-consistent model

terrain characteristics in 10-km resolution

• simple kinematics with “synthetic” reliefsand with a “real” relief

• some wet MAP cases simulations

the methodology

the W-E averaged slope towards North

the S-N averaged height - concavity

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kinematic vertical velocitiesby uniformSW wind

SouthWest

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kinematic vertical velocities by uniform S and SW wind

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if Trentino Mts. are removed

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if Julian Alpsand Dinarides are removed

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24-h MM5 simulation dry uniform S flow

MM5, dry uniform S flow Trentino Mts. removed

MM5, dry uniform S flow Dinarides removed

MM5 wet simulation MAP IOP5 potentially unstable - only Trentino subregion will be presented hereleft: original relief; right: Trentino Mts. removed.

top: vertical velocity; bottom: precipitation

IOP 5: vertical velocity at 700 hPa 4 Oct 99 06UTC

original relief

Trentino Mts. removed

IOP 5: 30hr precipitation accumulat. 4 Oct 99 06UTC

original relief

Trentino Mts. removed

IOP 9-10: vert. velocity at 700 hPa 24 Oct 99 00UTC

original relief

Trentino Mts. removed

IOP 9-10: 48hr precipitation accumulation 24 Oct 99 00UTC

original relief

Trentino Mts. removed

conclusions

• convexity/concavity seems to be important

• even the simpliest kinematics explains a lot of the climatological precipitation pattern

conclusions•in potentialy unstable MAP IOP 5 case the main role

of orograpical lifting was triggering; in Ticino and Trentino it was coupled with frontal

processes and “very intense convective cells”*) developed

• in stable MAP IOP 9-10 “a broad southwest current against the windward slopes was dominant feature of the dynamics” *) *) Robert Houze and Richard Rotunno: POC Science Director Notes

• especially in such cases the details of relief are essential