PowerPoint Presentation

Orographic PrecipitationEnhancement in MidlatitudeBaroclinic Storms:Results from MAP and IMPROVE II

Robert A. Houze and Socorro Medina

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Precipitation min on crest of Alps, max on lower slopes

20-year Alpine Autumn PrecipitationClimatology (rain gauge analysis by Frei and Schaer 1998)

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Major issue

Understand HOW microphysical processes areinvigorated to produce quick and efficient orographicenhancement in windward side flow

The Cascade Project

(Hobbs et al. 1973, Hobbs 1975)

Low concentration(large particles)

Liquid Water Content

Streamlines

Trajectories of ice particles growing by deposition and riming

High concentration(small particles)

What microphysical processes cangrow precipitation particles quickly?

Coalescence

T > 0 deg C

Aggregation

Riming

T < 0 deg C

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“Accretion”

How can the airflow make the accretionprocesses more active?

(Smith 1979)

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“Cellularity”

accretion

Potentially unstable upstream flow:

MAP IOPs 2b, 3, and 5

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IOP2b

IOP3

IOP5

Equivalent Potential Temperature

Milan sounding

12Z 03 Oct 99

00Z 26 Sep 99

12Z 20 Sep 99

Stable cases:

IMPROVE II Case 11

MAP IOP8

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IMPROVE II Experimental Area26 November-22 December 2001

PACIFIC OCEAN

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IMPROVE II Case 11: 13-14 December 2001

MM5 12 h forecast 500 mb height, wind, and temperature

Valid 00 UTC 14 Dec 01

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IMPROVE II Case 11Upstream soundings

IMPROVE II Case 11

Upstream Soundings of equivalent potential temperature

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IMPROVE II Case 11

3-hour Mean Radial Velocity

Horizontal distance (km)

Height (km)

S-Pol radar

ESE

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IMPROVE II Case 11

3-hour Mean Reflectivity

Horizontal distance (km)

Height (km)

S-Pol radar

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ESE

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IMPROVE II Case 11

Polarimetric Particle Identification over 3 hours

P3 aircraft data

Horizontal distance (km)

Height (km)

S-Pol radar

large aggregates and/or graupel

melting snow

weak echo snow

(high dBZ, low ZDR)

(high dBZ, high ZDR)

(low dBZ, low ZDR)

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ESE

Reflectivity

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IMPROVE II NOAA/ETLS-band Radar

13-14 December 2001

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IMPROVE II NOAA/ETLS-band Radar

13-14 December 2001

Radial Velocity

Ri0.25

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Time series atMcKenzie Bridge

during

IMPROVE IICase 11

Shear at

0.7 - 3.0 km(profiler)

Radialvelocity

(VP S-band)

Min radialvelocity at2-3 km(VP S-band)

Occurrence ofgraupel &/oraggregates(S-Pol)

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IMPROVE II Case 11

Track of P3 aircraft & S-Pol reflectivity at 1.5 deg elevation

160 km

1.6 mm

9.6 mm

IMPROVE II Case 11

Ice particle imagery from P3 aircraft

Stable cases:MAP IOP 8

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Equivalent Potential Temperature

IOP8

Milan sounding

18Z 20 Oct 99

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MAP IOP8

34-hour Mean radial velocity

S-Pol radar

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MAP IOP8

34-hour Mean Reflectivity

S-Pol radar

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MAP IOP8

Polarimetric Particle Identification over 34 Hours

S-Pol radar

weak echo snow (low dBZ, low ZDR)

melting aggregates (high dBZ, high ZDR)

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MAP IOP8

Reflectivity from vertically pointing S-band radarat Locarno Monti

Time UTC

Height (km)

OPRA radar

Yuter & Houze 2003

Heavy rain

0°C

TURBULENCE

Microphysicalenhancement

Conceptual model for orographic precipitationenhancement in stable, sheared upstream flow

Aggregation

Riming

Coalescence

TURBULENCE

Conclusions

Low-level growth by coalescence and/or riming is neededto make precipitation fall out quickly on lower slopes

Cellularity is required to make the coalescence and/orriming occur

Cellularity may occur by EITHER release of potentialinstability OR by turbulence in stable flow

In stable flow, cellularity is a manifestation of turbulence insheared flow rising over the terrain.

Cells in stable flow

favor particle growth byaccretion

have updrafts >1-3 m/s

contain aggregates and/orgraupel

enhance precipitationon lower slopes

Mixed case:MAP IOP 14

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Equivalent Potential Temperature

IOP14

Milan sounding

00Z 4 Nov 99

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MAP IOP14

Mean wind shear from Lonate profiler

Mean and SD over 16 hours

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MAP IOP14

34-hour Mean radial velocity

S-Pol radar

NNW

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MAP IOP14

34-hour Mean Reflectivity

S-Pol radar

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NNW

$C:\Documents and Settings\houze\My Documents\Talks\2003_MAP-Brig\fromSocorro\030506\xmicro_14.gif$

MAP IOP14

Polarimetric Particle Identification over 34 Hours

S-Pol radar

weak echo snow (low dBZ, low ZDR)

melting aggregates (high dBZ, high ZDR)

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NNW

$C:\Documents and Settings\Administrator\My Documents\WorkFiles\Talks\2003_Brig\opra_rf_IOP14.gif$

MAP IOP14

Reflectivity from vertically pointing S-band radarat Locarno Monti

Time UTC

Height (km)

OPRA radar

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IMPROVE II Case 11

Newport Wind Profiler Data

Mean and SD over 8 hours

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IMPROVE II Case 11

McKenzie Bridge Profiler Data

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Mean and SD over 8 hours

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MAP IOP8

Mean wind shear from Lonate profiler

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Mean and SD over 34 hours

“Even if we accept the idea that large-scale orographic liftingcan cause some release, it is … surprising in light of thedifficulties in forming precipitation-size particles, to find releaseefficiencies of 70% to 100%, … Is it possible to convert such ahigh fraction of the condensed water into precipitation?”

Ron Smith (1979)

Major issue

Understand HOW microphysical processes areinvigorated to produce quick and efficient orographicenhancement in windward side flow

A Microphysical Question