Relationships Between Gulf of California Moisture Surges and Tropical Cyclones in the Eastern Pacific Basin

1
Relationships Between Gulf of California Moisture
Surges and Tropical Cyclones in the Eastern
Pacific Basin
Wayne Higgins and Wei Shi Climate Prediction
Center / NCEP 29th Climate Diagnostics and
Prediction Workshop Madison, WI 18-22 October,
2004
2
Objectives

• To examine relationships between Gulf of
  California moisture surges and tropical cyclones
  using standard surface observations, the Regional
  Reanalysis circulation and moisture fields,
  tropical cyclone track data, and observed
  precipitation.
• To distinguish the precipitation and atmospheric
  circulation patterns for several categories of
  surge events, including those that are directly
  related, indirectly related and not related to
  TCs.

3
Data Set Selection

• Hourly Surface observations at Yuma, AZ
• Td, surface wind speed, and surface wind
  direction
• Precipitation
• US_Mexico daily precipitation analysis (Higgins
  et al. 2000)
• Resolution (lon, lat)(1.0x1.0)
• Tropical Cyclone (HURDAT) track data (NHC)
• Atmospheric Circulation and Moisture
• NCEP Regional Reanalysis (Mesenger et al. 2004)
• Period of Analysis July-August 1977-2001
• except 1992 in surface observations and 1977-78
  in RR

4
Identification of Surge Events

• Application of method given in Fuller and
  Stensrud (2000)
• Onset Characteristics
• Rapid increase in surface Td gt mean
• Surface winds gt mean
• Surface wind direction southerly
• 25-hr running means are used to avoid misleading
  aspects of the diurnal cycle in the desert
  (little impact on surge ID) .
• climatological mean July-August 1977-2001

5
Td (C), Wind Direction () and Wind Speed (m
s-1) at Yuma, AZ July-August 1986
W
W
S
S
S
S
S
S
Note Fuller and Stensrud (2000) identified
the same set of events.
6
Classification of Surge Events

• Surges at Yuma were further further classified
  based on their relationships to eastern Pacific
  TCs.
• TC-related A TC crosses 110W within 3 days of
  a surge at Yuma, AZ.
• Direct Influence If the TC center of
  circulation moves within 3 of Baja California,
  GOC, or Mexican mainland (poleward of 22 N)
  within 3 days of onset.
• Indirect Influence If the direct influence
  criterion is not satisfied.
• Not TC-related No TC crosses 110W within 3
  days of a surge at Yuma, AZ.

7
TROPICAL CYCLONE TRACKS IN THE REGIONAL REANALYSIS

direct
indirect
mean direct (RR)
mean indirect (RR)
mean direct (Obs.)
mean indirect (Obs.)

• The RR has realistic TC tracks that compare well
  to observations, so it is appropriate to use the
  circulation and moisture fields from RR to link
  the TCs and surges at Yuma, AZ.

8
Number () of Yuma Surges by Category
Surge Category Number of Events
All 142
TC-Related 65 (46)
Not TC-Related 77 (54)
Direct 38 (58)
Indirect 27 (42)
9
Classification of Surge Events(Higgins et al.
2004)

• Define strong, weak, wet, dry surges
• Strong Td gt climatological mean for at least 3
  days
• Weak Td gt climatological mean for less than 3
  days
• Wet positive precipitation anomalies in AZNM
  for the 5 day period (day 0 to day 4) after
  onset
• Dry negative precipitation anomalies in AZNM
  for the 5 day period (day 0 to day 4) after
  onset
• AZNMArizona/New Mexico (112.5-107.5W
  32-36N)

10
25-hr Running Mean Values of Td (C) at Yuma and
Daily Precipitation Anomaly (mm) in AZNM for
July-August 1986
(W)eak or (S)trong
W
W
S
S
S
S
S
S
Precip
Td
(W)et or (D)ry
D
W
W
W
W
D
D
D

• Some surges are associated with
  wetter-than-normal conditions in AZNM while
  others are associated with drier-than-normal
  conditions .
• This is somewhat independent of surge strength.

• AZNMArizona/New Mexico (112.5-107.5W
  32-36N)

11
Number () of Yuma Surges by Category

Surge Category TC-Related Not TC-Related Direct Indirect
Strong and Wet 29 (45) 21 (27) 19 (50) 10 (37)
Strong and Dry 17 (26) 14 (18) 12 (32) 5 (19)
Weak and Wet 9 (14) 18 (24) 4 (10) 5 (19)
Weak and Dry 10 (15) 24 (31) 3 (8) 7 (25)

• 45 of the TC-related surges are strong and wet,
  while only 27 of the surges
• not related to TCs are strong and wet
• 50 of surges with a direct relationship to TCs
  are strong and wet and 82 are strong.

12
Composite Evolution of Precipitation Anomalies
(mm) for Moisture Surges Keyed to Yuma

• All surges SE?NW progression of ve anomalies
  along the west coast
• The positive precipitation anomalies are much
  larger and more widespread for the TC-related
  surges than for surges not related to TCs.

13
Composite Evolution of Precipitation Anomalies
(mm) for Moisture Surges Keyed to Yuma

• Surges that are directly related to TCs have
  much larger ve anomalies over most of Mexico
  than those that are indirectly related.

14
Fraction () of Total Precipitation and
Accumulated Precipitation Anomalies (mm)
July-August 1977-2001 base period

• The fraction of surge-related precipitation
  during TC-related surges is larger than that
  during surges not related to TCs, yet TC-related
  surges account for less than half of the total
  surge events (65 of 142 events).

15
Fraction () of Total Precipitation and
Accumulated Precipitation Anomalies (mm)

• Most of rainfall during TC-related surges occurs
  when the TCs are directly related to Yuma
  surges, yet these cases are relatively rare (38
  events over 25 years).

16
Mean 925-hPa Vector Wind Anomalies (m s-1) and
Specific Humidity Anomalies (g kg-1)
The low-level southerly flow is stronger and
there is more low level moisture present in the
GOC region for the TC-related surges than for
surges not related to TCs
17
Mean 925-hPa Vector Wind Anomalies (m s-1) and
Specific Humidity Anomalies (g kg-1)
Differences between direct and indirect cases are
pronounced with moisture transport from the
southeast along the entire GOC in the direct
cases
18
Vertical Profiles of Wind Direction and Wind
Speed Anomalies (tenths of knots) and Specific
Humidity Anomalies (g kg-1)

• Surges that are directly related to TCs have
  dramatically stronger low-level southerly flow
  and the most significant increases in moisture
  along the GOC. Specific humidity anomalies are
  as large as 25 of the mean value at Puerto
  Penasco.

19
Vertical Profiles of Wind Direction and Wind
Speed Anomalies (tenths of knots) and Specific
Humidity Anomalies (g kg-1) along 110oW

• Surges with direct TC influences show a much
  stronger cyclonic signature in the wind
  field and larger moisture anomalies than those
  with indirect TC influences.

20
850-hPa Mean Vector Wind (m s-1) and Specific
Humidity (g kg-1) (July August 1979-2001)
21
Summary

• Relationships between gulf surges and eastern
  Pacific Tropical Cyclones (TCs) were examined.
• Emphasis was placed on the relative differences
  in precipitation and atmospheric circulation
  patterns for several surge categories
  (TC-related, not TC-related, direct and
  indirect).
• TC-related surges account for slightly less than
  half of all surges.
• Surges that are directly related to TCs have
  dramatically stronger low-level southerly flow
  and the most significant increases in moisture
  along the GOC. They occur on average about once
  per year, and are the most prolific rain
  producers.