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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
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climatology of Alpine precipitation by Schwarb, Daly, Frei and Schär
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flow deflection due to rotational effectsexplains the
secondary Alpine precipitation maximum in Ticino
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full lines: displacements thin lines: displacements
Buzzi and Tibaldi 1977Ro=0.7
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Schär and Schneidereit 2000
Ro 0.75
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Rotunno and Ferretti 2001(the 1994 case) deflection & gradient of potential stability
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Rotunno and Ferretti 2001(the 1994 case) deflection & gradient of potential stability
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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?
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what can we learnfrom the simpliest
kinematic simulation?this si not precipitation field!
it is terrain induced vertical velocity in the
mass-consistent model
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terrain characteristics in 10-km resolution
• simple kinematics with “synthetic” reliefsand with a “real” relief
• some wet MAP cases simulations
the methodology
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the W-E averaged slope towards North
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the S-N averaged height - concavity
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2 4 6 8 10
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Y A
xis
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synthetic reliefs
(similar to the ones of Schär and Schneidereitand of Rotunno and Ferretti)
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2 4 6 8 10
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2 4 6 8 10
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2 4 6 8 10
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kinematic vertical velocitiesby uniformSW wind
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SouthWest
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South
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kinematic vertical velocities by uniform S and SW wind
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2 4 6 8 10
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xis
2 4 6 8 10
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if Trentino Mts. are removed
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2 4 6 8 10
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Y A
xis
if Trentino Mts are removed
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2 4 6 8 10
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Y A
xis
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if Julian Alpsand Dinarides are removed
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2 4 6 8 10
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4
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X Axis
Y A
xis
if Julian Alpsand Dinarides are removed
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24-h MM5 simulation dry uniform S flow
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MM5, dry uniform S flow Trentino Mts. removed
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MM5, dry uniform S flow Dinarides removed
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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
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IOP 5: vertical velocity at 700 hPa 4 Oct 99 06UTC
original relief
Trentino Mts. removed
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IOP 5: 30hr precipitation accumulat. 4 Oct 99 06UTC
original relief
Trentino Mts. removed
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IOP 9-10: vert. velocity at 700 hPa 24 Oct 99 00UTC
original relief
Trentino Mts. removed
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IOP 9-10: 48hr precipitation accumulation 24 Oct 99 00UTC
original relief
Trentino Mts. removed
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conclusions
• convexity/concavity seems to be important
• even the simpliest kinematics explains a lot of the climatological precipitation pattern
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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