Upper Level Synoptic Influences on Cloud Top Height over Monterey Bay 1823 July 2005

1
Upper Level Synoptic Influences on Cloud Top
Height over Monterey Bay 18-23 July 2005

• LCDR Beth Sanabia
• OC 3570
• 13 Sep 05

2
Outline Motivation

• Background
• Method Tools
• Quick View
• Synoptic Situation
• Case Studies
• Naval Applications

• Background
• General
• Always foggy here
• What is going on synoptically that makes this
  happen?
• Difficult to accurately forecast height and
  persistence of both fog and dust
• Climatology
• EASTPAC High Location
• Location during at sea period in agreement with
  climatology
• EASTPAC High Relevance
• Drives subsidence which caps the inversion, often
  resulting in a layer of stratus clouds that
  blankets the coast of California.

Lentz Spring Transition over the Northern
California Shelf (Fig 2)
3
Method Tools

• Approach it in reverse (look at observed
  first)
• Identify
• cloud top height from radiosonde data
• point where the temp and dew point traces diverge
• potential case studies
• gt100m change in cloud top height
• Determine
• synoptic pattern
• mesoscale features
• Find
• correlation between upper level synoptic pattern
  cloud top height
• naval application, if any

• Observed data
• Radiosonde profiles
• MODIS GOES sat shots
• RV Pt Sur wx obs
• Ft Ord Profiler
• Modeled data
• GFS EASTPAC 18Jul/00z model run (300 500mb)
• GFS 300 500mb analysis twice daily during the
  cruise period
• Also considered
• 3km COAMPS
• CIMT wind graphics

4
denotes approximate ship location
5
Slide Layout next few frames
Valid Time
Synoptic Situation
12z, 17 July 05

• 300mb
• Overall
• Flow is zonal becoming meridional later in the
  period
• PFJ zonal, weakens, then reestablishes in the
  base of the LW trough in CENTPAC late in the
  period
• Relevant
• Cut off low ht center in central EASTPAC deepens
  then moves NE 21/12z crosses Oregon coast
  22/12z
• 500mb
• Overall
• Axis of the long wave trough sits along the
  Western Canadian border until 21/12z when it
  reorients to the SW.
• Relevant
• Cut off low ht center supported by PVA deepens
  then moves NE.
• Vortmax crosses the Oregon coast 22/12z

6
00z, 18 July 05
7
12z, 18 July 05
8
00z, 19 July 05
9
12z, 19 July 05
10
00z, 20 July 05
11
12z, 20 July 05
No image available
12
00z, 21 July 05
13
12z, 21 July 05
14
00z, 22 July 05
15
12z, 22 July 05
No image available
16
00z, 23 July 05
17
12z, 23 July 05
18
Repeat Synoptic Sequence
Synoptic Situation
12z, 17 July 05

• 300mb
• Overall
• Flow is zonal becoming meridional later in the
  period
• PFJ zonal, weakens, then reestablishes in the
  base of the LW trough in CENTPAC late in the
  period
• Relevant
• Cut off low ht center in central EASTPAC deepens
  then moves NE 21/12z crosses Oregon coast
  22/12z
• 500mb
• Overall
• Axis of the long wave trough sits along the
  Western Canadian border until 21/12z when it
  reorients to the SW.
• Relevant
• Cut off low ht center supported by PVA deepens
  then moves NE.
• Vortmax crosses the Oregon coast 22/12z

19
00z, 18 July 05
20
12z, 18 July 05
21
00z, 19 July 05
22
12z, 19 July 05
23
00z, 20 July 05
24
12z, 20 July 05
No image available
25
00z, 21 July 05
26
12z, 21 July 05
27
00z, 22 July 05
28
12z, 22 July 05
No image available
29
00z, 23 July 05
30
12z, 23 July 05
31
Wed 20 Jul 05
Tues 19 Jul 05
Mon 18 Jul 05
Images from Ft Ord profiler
Sat 23 Jul 05
Fri 22 Jul 05
Thurs 21 Jul 05
3
32
Case

• Timeframe
• Sonde 3
• 18 July 05 204545Z
• 134545L
• 310 meters
• Sonde 4
• 19 July 05 101959Z
• 031959L
• 450 meters

33
12z, 18 July 05
34
00z, 19 July 05
35
12z, 19 July 05
36
Case Analysis

• Review Results
• Sonde indicated a 140m increase in cloud top
  height in a 14 hour period
• No obvious synoptic indicators
• Increase was delayed, but also did occur at Ft
  Ord
• Assessment
• Smaller scale feature caused the increase
• Naval Applications
• No significant change in refractive conditions

18 July 05 204645Z 134645L
19 July 05 101959Z 031959L
37
Case

• Timeframe
• Sonde 14
• 22 July 05
• 000138Z
• 21 July 05
• 170138L
• 490 meters

• Sonde 15
• 22 July 05
• 050123Z
• 21 July 05
• 220123L
• 600 meters

38
12z, 21 July 05
39
00z, 22 July 05
40
12z, 22 July 05
No image available
41
Case Analysis

• Review Results
• Sonde indicated a 110m increase in cloud top
  height in a 4 hour period
• Synoptically Low height center approached the
  Oregon coast
• Increase at Ft Ord occurred prior to the one we
  observed at sea
• Assessment
• The upper level trough relaxed the subsidence,
  allowing the boundary layer to deepen.
• Naval Applications
• Altered the elevated duct
• Potential to impact radar propagation in and
  through that layer

22 July 05 000138Z 21 July 05 170138L
22 July 05 050123Z 21 July 05 220123L
42
Case

• Timeframe
• Sonde 20
• 23 July 05
• 005714Z
• 22 July 05
• 175714L
• 500 meters

• Sonde 21
• 23 July 05
• 064455Z
• 22 July 05
• 234455L
• 50 meters

43
12z, 22 July 05
No image available
44
00z, 23 July 05
45
12z, 23 July 05
46
Case Analysis

• Review Results
• Sonde indicated a 450m decrease in cloud top
  height in a 6 hour period
• Synoptically Trough axis passed over the West
  Coast
• Decrease was observed at Ft Ord
• Assessment
• The increased mixing with the upper level trough
  was sufficient to mix out the boundary layer
• Naval Applications
• Weakened the elevated duct
• Potential to impact radar propagation in and
  through that layer

23 July 05 005714Z 22 July 05 175714L
23 July 05 064455Z 22 July 05 234455L
47
Conclusions Comments

• Cause Effect
• Indicators of varying cloud top height may not
  always be obvious synoptically
• Normal Associations
• High Pressure Good Weather
• Low Pressure Bad Weather
• Intuition
• Upward vertical motion associated with the
  movement of the cutoff low across the California
  / Oregon creates turbulence which breaks the
  inversion and results in clearing skies (better
  weather).