The Monsoon Circulation, Typhoon Activity, and Island Rainfall in the Western North Pacific During the Past 50

Years: Recurring Patterns and Extreme Events

Mark A. Lander

Water and Environmental Research Institute of the Western Pacific

Central Guam mountains after amajor brushfire.

U

Pohnpei locator maps showing world setting and Pohnpei Island with Municipalities.

Climate of Micronesia

Climate Change?Who ya gonna believe? Me, or your own eyes? *

My own rules of thumb: Warwick Rhode Island 1960s, 1970s

First touch of frost: Last week of September

First hard freeze: Last week of October

First day max temp < freezing: Last week of November

These events now occur 2 or 3 weeks later !!

* Groucho Marx

Commonly cited recent climate anomalies

Climate change during my lifetime

Global Cooling

Global Warming

Climate Variability in USAPI during the past 50 years

• Very large year-to-year changes Annual Rainfall on Guam 50 inches to 150 inches

• Tropical Cyclones WNP Basin annual number: 20 to 40!

• ENSO

• Monsoon flow pattern

Weather makers in USAPI

• Tropical Cyclones• Monsoon trough• TUTT/TUTT Cells• ENSO• Mesoscale Convective Systems

If you’re going to change the climate of Micronesia you have to change the climate of these !

Climate of Pacific Islands1500 years BP to now

(MWP through LIA to current)

Problems:• No direct measurements, none that go

back more than 100 years (50, at best in many locations)!

• Proxy records conflicting, and yield some almost inexplicable local climate and climate changes (e.g., Washington Island).

Question for Group

• Can one use very recent global temperature behavior as proxy for larger and longer transitions: e.g., MWP to LIA?

-- Investigate positions of ITCZ and rainfall on Washington Island before, during and after the “Time Magazine Ice Age”

-- 1988 very cold La Nina-related cold water

What did it do to ITCZ?

9000

10000

1876

1880

1884

1888

1892

1896

1900

1904

1908

1912

1916

1920

1924

1928

1932

1936

1940

1944

1948

1952

1956

1960

1964

1968

1972

1976

1980

1984

1988

1992

1996

2000

2004

-50

-40

-30

-20

-10

0

10

20

30

40

Southern Oscillation Index

1988 had very cold equatorial waters. Check position of ITCZ

1988

MONSOON

Summer Monsoonof the western North

Pacific

Normal surface flow pattern(black = westerly)VS 1997(dashed-line filled = westerly).

Summer Monsoon

Surface wind flow, August 1997

Palau

Strongest Westerly Wind Burst ever Observed ! (December 1996)

Normal Monsoon

40 N

30 N

20 N

10 N

EQ100 E 140 E 160 E 180120 E

Guam

Saipan

Pohnpei Majuro

Reverse Oriented Monsoon Trough

40 N

30 N

20 N

10 N

EQ100 E 140 E 160 E 180120 E

12

3Guam

Saipan

Pohnpei Majuro

Next Trough Develops

40 N

30 N

20 N

10 N

EQ100 E 140 E 160 E 180120 E

Guam

Saipan

Pohnpei Majuro

Permian Surface winds and rainfall

Cold Tongue

The MJO

C

C

EQ

21

Put the only heat source of the entire planet over the Maritime Continenent:Easterly winds would extendacross the whole Pacific, Atlanticand to East Africa. Westerlieswould extend across the Indian Ocean.

GUAM

TC CRAIGTC ERICA

TC ESETA

SHEAR LINE

NW MONSOON

W

GMS IR 00 UTC 22 OCT

TDTD

KetsanaParma

TD??

GMS IR 00 UTC 22 OCT

TDTD

KetsanaParma

TD??Reverse-orientedMonsoon Trough

W

Super Typhoon Paka (December 1997)

Majuro

When low latitudewinds go westerly, clouds and rain are found in maxwest wind band andin associated TCs.

W.I.

Question for Group:

• How much was this flow pattern changed by past 1500-year climate changes and how much can it be changed by anticipated global warming?– Location of STR, monsoon trough, TUTT, typhoon

tracks

– ENSO effects

– Large-scale features similar even in Permian!!

Question for Group:

• Washington Island bone dry?– There would almost have to be a cold tongue (i.e., not major El Nino like all the time).

– Christmas Island also dry?• Then ITCZ must either be most of the time in the Southern

Hemisphere, or ITCZ is pushed to the north of W.I. for much of the year. (check on 1988 – a year with an extensive cold tongue).

– Meteorological “Equator” currently at 7 North!!– Palau now dry only because of El Nino (+1) and during

typical September when the monsoon trough moves well to the north.

ENSO

Micronesia Rainfall in a Warmer World

1998 HNL conference:Reduction in mean annual rainfall from shift in ENSO * More El Nino Like most of the time * More Large El Nino’s

Southern Oscillation IndexRunning Sum

-120

-100

-80

-60

-40

-20

0

20

40

1866

1870

1874

1878

1882

1886

1890

1894

1898

1902

1906

1910

1914

1918

1922

1926

1930

1934

1938

1942

1946

1950

1954

1958

1962

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

2006

July 1976

Catastrophic floodingIn the Marquesas

Micronesia-wideSevere Drought

Eastern MicronesiaDeadly Typhoon

1998

1992

1983

ENSO Time Series (SOI)

-150

-100

-50

0

50

1866

1870

1874

1878

1882

1886

1890

1894

1898

1902

1906

1910

1914

1918

1922

1926

1930

1934

1938

1942

1946

1950

1954

1958

1962

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

RED = Running Sum of time series: 0.4*(month-1) + 0.3*(month-2) + 0.1*(month-3) + RANDOM NUMBER

DARK BLUE = RUNNING SUM OF SOI 1866-2002

Pacific Interannual and Interdecadal Variability

• There is ONLY ENSO. Time series is autoregressive (several months)

with stochastic forcing. Spectral Peak at ~ 2.6 years.

• Pacific Decadal Oscillation is reddened ENSO. Time series and fields are similar, but with

longer memory because of mid-latitude mixed-layer deepening.

PDO is reddened ENSO

Question for Group:

• Has ENSO been affected by climate changes in the past 1500 years?

Frequency, strength, character

• ENSO affects almost everything in USAPI: Tropical cyclone distribution, rainfall, sea level, monsoon trough

position, and extreme events of weather elements.

1998 Climate workshop East-West Center

Consider ENSO in a warmer world:

More frequent strong El Nino’s like 1982-83 and 1997-98?

or

Climate more El Nino-like all the time?

Question: Is this the model for the past 1500 years?(MWP and LIA ??)

ENSO

RAINFALL

Micronesia Rainfall by Hour

GUAM ANNUAL RAIN

NOTE: POST-EL NINO YEARS IN RED

0

20

40

60

80

100

120

140

160

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

NOTE: RED INDICATES POST EL NINO YEARS

NORMAL

0

20

40

60

80

100

120

140

160

180

200

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

AN

NU

AL

RA

IN (

INC

HE

S)

KOROR ANNUAL RAIN

MAJURO ANNUAL RAIN

0

20

40

60

80

100

120

140

160

180

200

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

NORMAL

NOTE: POST-EL NINO YEARS IN REDPOHNPEI ANNUAL RAIN

NOTE: POST-EL NINO YEARS IN RED

0

50

100

150

200

250

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

1992

Guam Rainfall VS Water Table

-60

-40

-20

0

20

40

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

Integrated Guam Rainfall Anomaly (Red) VSObserved A20 Wellhead (Blue)

LONG-TERM SURPLUSES AND DEFICITS (Pohnpei)

-120

-70

-20

30

80

130

180

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

JANUARY OF POST-EL NINO YEAR

Pohnpei Rainfall

-6000

-4000

-2000

0

2000

4000

6000

8000

1926

1928

1930

1932

1934

1936

1938

1940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

DR

Y

--

----

W

ET

-20

-10

0

10

20

30

40

Manoa Rainfall 1921-2007 Running Accumulation

Extreme Value Analysis

0.1

0.3

0.2

0.50.4

0.6

0.8

1.0

6.05.04.0

3.0

2.0

15.0

10.0

8.0

5 10 20 30 40 50 60 2 3 4 5 6 8 1012 18 24IN MINUTES IN HOURS

DURATION

Saipan Int. Airport with

consideration of typhoons

5

20

50

100 Pongsonaon Guam

10

Pohnpeiwet day

Oct 29, 2003

INCHES

PER

HOUR

IDF chart of selected return periods at the SIA (blue dots connected by blue dashed lines). Because the cause of the extreme events is typhoons, this curve may be considered applicable for all of Saipan. The intensity-duration values measured during Typhoon Pongsona on Guam (red dots connected by red dotted line) are shown. Also, the highest Intensity-duration values measured by a newly installed rain gauge network on Pohnpei have been plotted (green dots connected by green dotted line). Without typhoons, the return-periods at all durations would be much lower.

HEAVY RAINFALL IN A TYPHOON

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

LOCAL TIME (08 DEC 2002)

RA

INF

AL

L (

INC

HE

S)

PONGSONA RAINFALL TIME SERIESAT ANDERSEN AFB

EYE PASSAGE

Max = 175 mm/hr

Questions for Group:

• How have past 1500-year climate changes affected rainfall in USAPI?

• Can USAPI extreme rainfall events be affected by global climate changes such as MWP, LIA and anticipated AGW?

• Do typhoons produce the highest rain rates at all intervals: 15 minute to 24 hour?

Questions for Group:

• Is the overall rainfall in the tropics heavier in a warmer world? *

– * I have outstanding bet with Bob Livezy regarding Singapore rainfall over the past 50 years.

• Or, are only the values of extreme rainfall elevated in a warmer environment?

– e.g., Trenberth’s claim of Katrina 7% more rain because of AGW

– Every cloud affected? Or just typhoons? (The Katrina Effect)

TYPHOONS

SUNDAY MORNING, 8 December 2002

Guam

Rota

TinianWMO International Workshop on

Tropical CycloneLandfall

Processes. Macao, China. (21- 25 March

2005)

M. LanderSlide 16

WMO International Workshop on

Tropical CycloneLandfall

Processes. Macao, China. (21- 25 March

2005)

M. LanderSlide 9

Western North Pacific Tropical Cyclone Variability

-25

-15

-5

5

15

25

35

-25

-15

-5

5

15

25

35

TS + TY

TY

JTWC Running sum of annual anomalies

1960 1970 1980 1990 2000

Active

Active

QuietQuiet

145 E

18 N

15 N

12 N

1970-79

145 E

18 N

15 N

12 N

1980-89

18 N

15 N

12 N

145 E1990-99

145 E

18 N

15 N

12 N

1970-99

Tropical Cyclone Locations

More?

Anatahan

Saipan

Tinian

Rota

Guam

140 E 150 E145 E

15 N

10 N

15 N

10 N

140 E 145 E 150 E

20

20

30

40

50

60

7080

90

100

100

90

80

70

7080 80

7060

5040

40

30

40

50

Contours (at intervals of 10) show the number of tropical storms and typhoons per 100-years expected to pass within 75 nautical miles from any map location. Analysis is based on the years 1945-97. Chart adapted from Guard, et al. (1999). Note that on this fine scale, Guam appears to have a slightly higher risk of a tropical storm or a typhoon than Saipan (60 per 100-years, versus 50 per 100-years).

PEAC Typhoon Risk Assessment

EQ

10N

20N

30N

100E 120E 140E 160E 180

"El Nino Box"

19981997

INCREASED Threat for Marshalls and GuamNEUTRAL for CHUUK (End of El Nino Year)

CHUUK

Majuro

YAP Guam

Western North Pacific Tropical Cyclone Distribution*

40 N

30 N

20 N

10 N

EQ100 E 140 E 160 E 180120 E

1

1

1

2

2

3

3

4

5

Guam

Saipan

* Tropical cyclones per 5 x 5 square per year

2007 Tropical Cyclone Distribution

EQ

10N

20N

30N

100E 120E 140E 160E 180

"El Nino Box"

20071997

Guam

Guam/CNMI For all of June, July, August and September, the weather on Guam has been rather tranquil. Winds have been very light (easterly for the most part, with a few periods of light westerly wind flow), only one tropical cyclone (Man-Yi) adversely affected the island (it generated near-gale winds for one day in early July), and there have been no extreme island-wide heavy rainfall events. In association with La Niña, monsoon southwest winds remained mostly to the west of Guam, and tropical cyclone development was also pushed to the west and north of Guam. In an environment of light wind, rainfall was produced on-island by short-lived (6-12 hr) mesoscale convective systems, and by isolated (mostly daytime) thunderstorms that affected only parts of the island on any given day. Daytime thunderstorms have produced isolated heavy rainfall totals near 2 or 3 inches in a few hours at some locations, however, over the course of a month, rainfall amounts in this weather pattern tend to average near to slightly below normal. …..

(PEAC 4th QTR 2007 Newsletter)

2007 Tranquility

Questions for Group:

• How have past 1500-year climate changes affected typhoon climate in USAPI?

• More typhoons in a warmer world?• More very intense typhoons (overall) or

as a higher proportion of all typhoons in a warmer world? (vice versa for a colder world? LIA ??)– Note 2007 Tranquility

• Track changes?

Final Questions for Group:

• How have past 1500-year climate changes affected typhoon climate in USAPI?

• Can we investigate this by studying changes to rainfall, typhoons, and extreme events during observed large departures from average climate during the past 50 to 100 years? Extrapolate to MWP and LIA?

Photo Courtesy of Roger Edson

Smoke from fuel fire

Sand from overwash

ENDSunset on Guam Post TY Pongsona