# Presentation: 919704

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

**Wayne Higgins and Wei Shi**
**Climate Prediction Center / NCEP**
**   ****29****th**** Climate Diagnostics and Prediction Workshop**
**Madison, WI**
**18-22 October, 2004**

## 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 TC’s.

## 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)=(1.0°x1.0°)
-  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

## Identification of Surge Events

-  **Application of method given in Fuller and Stensrud (2000)**
-  **Onset Characteristics:**
-  Rapid increase in surface Td  > mean*
-  Surface winds > 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

## Td ( ̊C), Wind Direction ( ̊) and Wind Speed (m s-1) at Yuma, AZ July-August 1986

_**T**__**d**__** (**__** ̊C), Wind Direction ( ̊) and Wind Speed (m s**__**-1**__**) at Yuma, AZ July-August 1986**_

- W

- W

**S**

**S**

**S**

**S**

**S**

*** Note:  Fuller and Stensrud (2000) identified the same set of events.**

**S**

## Classification of Surge Events

-  **Surges at Yuma were further further classified based on their relationships to eastern Pacific TC’s.**
-  _**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.

## TROPICAL CYCLONE TRACKS IN THE REGIONAL REANALYSIS

_**TROPICAL CYCLONE TRACKS IN THE REGIONAL REANALYSIS**_

-  **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 TC’s and surges at Yuma, AZ.**

- direct

- indirect

- mean direct (RR)

- mean indirect (RR)

- mean direct (Obs.)

- mean indirect (Obs.)

## 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%) |

## Classification of Surge Events(Higgins et al. 2004)

-  **Define** **strong, weak, wet, dry surges**
-  **Strong:** Td > climatological mean for at least 3 days
-  **Weak:** Td  > 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
-  * **AZNM**:Arizona/New Mexico (112.5°-107.5°W; 32°-36°N)

## 25-hr Running Mean Values of Td ( ̊C) at Yuma and Daily Precipitation Anomaly (mm) in AZNM* for July-August 1986

_**25-hr Running Mean Values of T**__**d**__** (**__** ̊C**__**) at Yuma and **__**Daily Precipitation Anomaly (mm) in AZNM**__*****__** for July-August 1986**_

- W

- W

**S**

**S**

**S**

**S**

**S**

**S**

- D

- W

- W

- W

- W

- D

- D

- D

**(W)eak or (S)trong**

- Td

- Precip

**(W)et or (D)ry**

- * **AZNM**:Arizona/New Mexico (112.5°-107.5°W; 32°-36°N)

-  **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.**** **

## Number (%) of Yuma Surges by Category

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

| 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%) |

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

_**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 TC’s. **** **

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

_**Composite Evolution of Precipitation Anomalies (mm) **__**for Moisture Surges Keyed to Yuma**_

-  **Surges that are directly related to TC’s have much larger +ve anomalies over most of Mexico than those that are indirectly related.****   **

## Fraction (%) of Total Precipitation 

_**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 TC’s, yet TC-related surges account for less than half of the total surge events (65 of 142 events).**

## Fraction (%) of Total Precipitation 

_**Fraction (%) of Total Precipitation **_
_**and Accumulated Precipitation Anomalies (mm)**_

## Mean 925-hPa Vector Wind Anomalies (m s-1) and 

**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 TC’s**

**Mean 925-hPa Vector Wind Anomalies (m s****-1****) and **
**Specific Humidity Anomalies (g kg****-1****)**

## Mean 925-hPa Vector Wind Anomalies (m s-1) and 

**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**

## Vertical Profiles of Wind Direction and Wind Speed Anomalies 

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

## Vertical Profiles of Wind Direction and Wind Speed Anomalies 

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

## 850-hPa Mean Vector Wind (m s-1) and Specific Humidity (g kg-1)

- (July – August 1979-2001)

## 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 TC’s 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. **