radars in the mountains germann, mch. atmosphere is very layered 3 flow regimes evident but really...
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Radars in the Mountains
Germann, MCH
Atmosphere is very layered
3 flow regimes evident but really 5?
5 layers?
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2345
Vertical profile of reflectivity
Orographic Precipitation
Rain shadow
FOEHN, no rain
H3km
The Alps
Lee Side Suppression
Two Conceptual Models of Orographic Precipitation
Medina and Houze, 2003
Precipitation is on the flow when the flow is blocked.
Radial velocity Reflectivity
Precipitation is on the mountain crest when the flow is “up and
over”.
A little of both!
Precipitation is very sensitive to evaporation and sublimation – no precipitation reached
the ground
Melting is obvious but what is magical about 20 dBZ?
Snow processes can be very shallow!
Examples of very shallow precipitation
VPR/Process Classification Hourly sampling/manual
classification
Summary
• Shallow Weather– Focus on drizzle as an example to explain
detectability and measurability– Observability is a function of the radar too (MDS,
beamheight, beamwidth)– A few simple but key calculations to explain (not
calibration, not attenuation) – A little insight into “radar meteorology”
• A few case examples– Drizzle, snow, lake effect snow, orographic
Freezing Level and Mountain Sited Radars
Time-Height TemperatureFreezing Level from Radiosondes
March 2008 Payerne
July 2008 Payerne
Most of the time, the radar sees snow!
Erzgebirge
Ore m
ountains, grey
Doppler
No rain
No rain
1h accumulation
No rain
Accumulations
Stable Case: Blocked Flow from South
North South
ALPS
Precipitation on plains, Italy
Flow is blocked, flow is towards the south
MAP IOP-8 Medina and Houze, 2003
Radial Velocity - Blocked Flow
Medina and Houze, 2003
Unstable Case: Up and Over
Precipitation is on the first range
No blocked flow. Flow is from the south
Medina and Houze, 2003
Radial Velocity – Up and Over
Medina and Houze, 2003
Lee Side Troughing
On a very small terrain feature
Southern Ontario is relatively flat. Elevations rise from about 200m on Lake Huron to about 400m just south of Georgian Bay.
Lake
Huron
Lake Ontario
Lake Erie
Georgian Bay
Topography of Southern Ontario
Topography of Southern Ontario
Average of six GOES images over a 3-hour period
Moderate WSW flow
Dissipation of thin SC cloud in downslope flow
SC cloud formingbeneath an inversionat 1500 m above ground
Dissipation of Clouds in a SW Flow
Topography of Southern Ontario
Niagara Escarpment
Average of six GOES images over a 3-hour period