slide1
Download
Skip this Video
Download Presentation
Socorro Medina, Robert Houze, Christopher Williams and David Kingsmill

Loading in 2 Seconds...

play fullscreen
1 / 53

Socorro Medina, Robert Houze, Christopher Williams and David Kingsmill - PowerPoint PPT Presentation


  • 90 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Socorro Medina, Robert Houze, Christopher Williams and David Kingsmill' - pippa


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1
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

slide3

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)

slide4

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)

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]

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

slide22

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)

slide23
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

slide25

Upstream stability profiles for

storms with shear layer

STABLE

UNSTABLE

slide26

Richardson number (Ri)

for storms with shear layer

Ri = Nm2 / [dU/dz]2

slide27

Shear layer

m s-1

Case 11

m s-1

E

RADAR

E

W

slide30

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

slide51

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

slide52

Ticino

DOW

Toce

Po Basin

S-Pol

Milan

DOW Radar observations

Radial velocity (m s-1)

Shear (m s-1 km-1)

ad