Structure of mid-latitude cyclones crossing the California Sierra Nevada as seen by vertically point...
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Structure of mid-latitude cyclones crossing the California Sierra Nevada as seen by vertically pointing radar. Socorro Medina, Robert Houze, Christopher Williams and David Kingsmill. International Conference on Alpine Meteorology (ICAM), Rastatt , Germany, 15 May 2009.

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Socorro medina robert houze christopher williams and david kingsmill

Structure of mid-latitude cyclones crossing the California Sierra Nevada as seen by vertically pointing radar

Socorro Medina, Robert Houze, Christopher Williams and David Kingsmill

International Conference on Alpine Meteorology (ICAM), Rastatt, Germany, 15 May 2009


Previous studies of extratropical cyclone passage over complex terrain

Previous studies of extratropical cyclone passage over complex terrain

Alps (MAP)

Cascades (IMPROVE-2)

NOAA vertically

pointing (VP) radar

ETH vertically

pointing (VP) radar


Socorro medina robert houze christopher williams and david kingsmill

REFLECTIVITY (dBZ)

REFLECTIVITY (dBZ)

Alps VP radar data

Cascades VP radar data

09:00 08:00

01:00 00:00

 Time (19991021)

 Time (20011214)

RADIAL VELOCITY (m s-1)

RADIAL VELOCITY (m s-1)

OBSERVATIONS IN MIDDLE SECTOR OF

STORM, IN STATICALLY STABLE LAYER

WITH STRONG VERTICAL SHEAR

 TURBULENCE

09:00 08:00

01:00 00:00

 Time (19991021)

 Time (20011214)


Socorro medina robert houze christopher williams and david kingsmill

Conceptual model of dynamical and microphysical mechanisms active when the middle sector of extratropical cyclone passes over a windward slope

Updrafts ~1-3 m/s

Cell width ~1-5 km



Houze and Medina 2005


Objectives

Objectives

  • Extend the studies of extratropical cyclone passage over complex terrain to California’s Sierra Nevada

  • Inquire about repeatability of overturning, turbulent cells

  • Seek a deeper understanding of this mechanism


Dataset

Dataset

  • From the HydrometeorologicalTestbed that the US National Oceanic and Atmospheric Administration (NOAA) has been conducting in the Sierra Nevada (Ralph et al. 2005)

  • Expands over three winter seasons (2005/06, 2006/07, and 2007/08)

  • Main dataset from the vertically pointing (VP) S-band radar located at ‘Alta’

  • Complemented by GOES, North American Regional Reanalysis (NARR), soundings and weather surveillance radar data


Analysis of the alta vp dataset

Analysis of the Alta VP dataset

We find all the time periods that have stratiform precipitation that is deep (reflectivity > 0 dBZ from surface to 4 km height) and long lasting (> 2 hours)  57 “events” are found

 Time (4 Jan 2008)


Analysis of the alta vp dataset1

Analysis of the Alta VP dataset

We find all the time periods that have stratiform precipitation that is deep (reflectivity > 0 dBZ from surface to 4 km height) and long lasting (> 2 hours)  57 “events” are found

We investigate the upward motions for these events


Vp alta data for 04 jan 2008 estimate of upward motions using perturbation radial velocity

VP Alta data for 04 Jan 2008 Estimate of upward motions using perturbation radial velocity

Reflectivity

(Z = [dBZ])

Radial

Velocity [m/s]

1 hr running mean

radial velocity [m/s]

Perturbation radial

velocity [m/s]


Analysis of the alta vp dataset2

Analysis of the Alta VP dataset

We find all the time periods that have stratiform precipitation that is deep (reflectivity > 0 dBZ from surface to 4 km height) and long lasting (> 2 hours)  57 “events” are found

We investigate the upward motions for these events

These calculations indicate that ~10 (out of a total of 57 events) have clearly defined, intermittent up and downdrafts, similar to what was seen in the Oregon Cascades and the Alps


Analysis of the alta vp dataset3

Analysis of the Alta VP dataset

We find all the time periods that have stratiform precipitation that is deep (reflectivity > 0 dBZ from surface to 4 km height) and long lasting (> 2 hours)  57 “events” are found

We investigate the upward motions for these events

These calculations indicate that ~10 (out of a total of 57 events) have clearly defined, intermittent up and downdrafts, similar to what was seen in the Oregon Cascades and the Alps

Example of 4 Jan 2008 (case shown before)


Socorro medina robert houze christopher williams and david kingsmill

Synoptic setting of 4 Jan 2008 caseInfrared satellite temperature (~15 UTC)


Synoptic setting of 4 jan 2008 case 850 mb temperature 15 utc

Synoptic setting of 4 Jan 2008 case 850 mb temperature – (15 UTC)

NARR


Oakland sounding 15 utc 04 jan 2008

Oakland sounding - 15 UTC 04 Jan 2008


Conclusions

Conclusions

  • Intermittent cells were clearly defined in at least ~17% of the deep, long lasting stratiform events in the Sierra Nevada

  • Case study analysis suggest that the updrafts occur as the middle sector of the storm passes over the windward slopes, in a statically stable layer and in a region of strong vertically shear  i.e., similarly to what was observed in other mountain ranges

FUTURE STEP: Analyze the distribution of updraft magnitude

in relationship to shear, static stability, precipitation, etc


Vp alta data for 04 jan 2008 estimate of upward motions using perturbation radial velocity1

VP Alta data for 04 Jan 2008 Estimate of upward motions using perturbation radial velocity

Perturbation radial

velocity [m/s]


Aircraft observations across the snowy range wyoming

Aircraft observations across the Snowy Range, Wyoming

Geerts et al. 2008


Aircraft observations across the snowy range wyoming1

Aircraft observations across the Snowy Range, Wyoming

Geerts et al. 2008


Precipitation pattern typical of maritime cyclones moving toward us west coast

Precipitation pattern typical of maritime cyclones moving toward US west coast

Nagle and Serebreny 1962


Socorro medina robert houze christopher williams and david kingsmill

Farber (1972) found a pronounced orographic effect in the middle sector:

“pockets of moisture are observed in liquid water content meter”

“There are pockets of excessively high crystal concentration which

appear to be directly proportional to the amount of turbulence in the region”

“turbulence near the surface, originating from local topographical

features as well as strong vertical wind shears”

Houze and Medina (2005)


Socorro medina robert houze christopher williams and david kingsmill

Results from Farber (1972) and Hobbs (1975): Aircraft study of mid-latitude cyclones over the WA Cascades

LATE

(Post-frontal)

EARLY

(Pre-frontal)

MIDDLE

(Transitional)

Instability increases

Cloud tops decrease

Ice crystals decrease

LWC:

low

high

moderate

# Aggregates:

moderate &

constant

variability,

locally high

low

Turbulence:

low

high

high


Socorro medina robert houze christopher williams and david kingsmill

Upstream stability profiles for

storms with shear layer

STABLE

UNSTABLE


Socorro medina robert houze christopher williams and david kingsmill

Richardson number (Ri)

for storms with shear layer

Ri = Nm2 / [dU/dz]2


Socorro medina robert houze christopher williams and david kingsmill

Shear layer

m s-1

Case 11

m s-1

E

RADAR

E

W


04 jan 2008 alta reflectivity and residual radial velocity

04 Jan 2008 ALTA reflectivity and residual radial velocity


Socorro medina robert houze christopher williams and david kingsmill

VP Alta data for 04 Jan 2008

Estimate of upward motions by subtractingfallspeed

Reflectivity

(Z = [dBZ])

Radial

Velocity [m/s]

Fallspeed of

snow [m/s] =

0.817 Z 0.063

(Atlas et al. 1973)

Vertical motion

[m/s]


Radial velocity 15 utc 04 jan 2008 kdax

Radial velocity – 15 UTC 04 Jan 2008 (KDAX)

m s-1

-30.9

-18.0

-7.7

-0.5

0.0

7.7

18.0

30.9

2.4 deg elevation scan, 25 km rings


0700 utc 03 jan 2020 utc 04 jan 2008 accumulated precipitation kdax 50 km rings

0700 UTC 03 Jan – 2020 UTC 04 Jan 2008 Accumulated precipitation KDAX (50 km rings)


Synoptic setting of 4 jan 2008 case 500 mb geopotential height 15 utc

Synoptic setting of 4 Jan 2008 case 500 mb geopotential height – (15 UTC)

NARR


Synoptic setting of 4 jan 2008 case 900 mb specific humidity narr

Synoptic setting of 4 Jan 2008 case900 mb specific humidity (NARR)


15 utc 04 jan 2008 800 mb specific humidity narr zoom

15 UTC 04 Jan 2008 800 mb specific humidity (NARR) - zoom


15 utc 04 jan 2008 700 mb zonal wind narr zoom

15 UTC 04 Jan 2008 700 mb zonal wind (NARR) - zoom


15 utc 04 jan 2008 700 mb meridional wind narr zoom

15 UTC 04 Jan 2008 700 mb meridional wind (NARR) - zoom


Synoptic setting of 4 jan 2008 case 850 mb temperature narr

Synoptic setting of 4 Jan 2008 case 850 mb temperature (NARR)


15 utc 04 jan 2008 zonal and meridional winds narr

15 UTC 04 Jan 2008 zonal and meridional winds - NARR


4 jan 2008 case shs sounding

4 Jan 2008 case – SHS sounding


Case study 30 31 may 2005

Case study 30-31 May 2005


Case study 30 31 may 20051

Case study 30-31 May 2005


Case study 30 31 may 20052

Case study 30-31 May 2005


30 31 dec 2005 case shs sounding

30-31 Dec 2005 case – SHS sounding


Shear and billows in map

Shear and billows in MAP


Socorro medina robert houze christopher williams and david kingsmill

Ticino

DOW

Toce

Po Basin

32

16

S-Pol

0

Height above radar (km)

-16

0 2 4 6

-32

Milan

0 2 4 6 8 10 12 14 16 18 20 22 24

Distance from the radar (km)

DOW radar radial velocity (m s-1) Down-valley direction


Socorro medina robert houze christopher williams and david kingsmill

Ticino

DOW

Toce

Po Basin

S-Pol

Milan

DOW Radar observations

Radial velocity (m s-1)

Shear (m s-1 km-1)


Socorro medina robert houze christopher williams and david kingsmill

Time series of DOW derived observations


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