Transcript An Alert Classification System for Monitoring and Assessing the ENSO-Cycle

An Alert Classification System for
Monitoring and Assessing the ENSO-Cycle
A Briefing for the Committee for Climate Analysis,
Monitoring, and Services (CCAMS)
Mike Halpert
Deputy Director, CPC
30 October 2007
Kousky, V. E. and R. W. Higgins, 2007: An Alert Classifications System for monitoring and
assessment of the ENSO cycle, Weather and Forecasting, Vol. 22, No. 2, 353–371.
PURPOSE
• Informational briefing to familiarize the Climate
Analysis, Monitoring, and Services (CCAMS)
Committee with the ENSO Alert System, which will be
implemented in CPC Forecast Operations.
Overview
• An ENSO Alert System that includes Watches, Advisories, and a five-class ENSO Intensity Scale
(EIS) for warm & cold phases of the cycle is introduced.
• The ENSO Alert System is currently being tested in CPC Forecast Operations. An Official
Release is anticipated during FY09.
• CPC's monthly Climate Diagnostics Bulletin and ENSO Diagnostic Discussion will serve as the
primary vehicles for disseminating real-time information concerning the ENSO Alert Status to the
scientific community and public at large.
• An objective method that relates the EIS to impacts is introduced to improve operational
assessments of El Niño and La Niña impacts (analogous to what is done for hurricane and
tornado damage assessments using the Saffir-Simpson and Fujita scales, respectively).
(Note: Covered in Back-up Slides)
Oceanic Niño Index (ONI)
• The ONI is based on SST departures from average in the
Niño 3.4 region, and is a principal measure for
monitoring, assessing, and predicting ENSO.
• Defined as the three-month running-mean SST departures
in the Niño 3.4 region. Departures are based on a set of
improved homogeneous historical SST analyses
(Extended Reconstructed SST – ERSST.v2). The SST
reconstruction methodology is described in Smith and
Reynolds, 2003, J. Climate, 16, 1495-1510.
• Used to place current events in historical perspective.
• NOAA’s operational definitions of El Niño and La Niña are
keyed to the ONI index.
ONI: Evolution since 1950
El Niño
neutral
La Niña
NOAA Operational Definitions for
El Niño and La Niña
El Niño: characterized by a positive ONI greater than or
equal to +0.5°C.
La Niña: characterized by a negative ONI less than or
equal to -0.5°C.
To be classified as a full-fledged El Niño or La Niña
episode these thresholds must be exceeded for a period
of at least 5 consecutive overlapping 3-month seasons.
CPC considers El Niño or La Niña conditions to occur when the monthly
Niño3.4 SST departures meet or exceed +/- 0.5°C along with consistent
atmospheric features.
Historical El Niño and La Niña episodes,
based on the ONI computed using ERSST.v2
Warm Episodes
max
Cold Episodes
min
JAS 1951 - NDJ 1951/52
MAM 1957 – MJJ 1958
0.7
1.6
ASO 1949 – FMA 1951
MAM 1954 – DJF 1956/57
-1.8
-2.1
JJA 1963 – DJF 1963/64
1.0
ASO 1961 – MAM 1962
-0.6
MJJ 1965 – MAM 1966
1.6
MAM 1964 – JFM 1965
-1.1
OND 1968 – AMJ 1969
1.0
SON 1967 – MAM 1968
-0.9
ASO 1969 – DJF 1969/70
0.7
JJA 1970 – DJF 1971/72
-1.4
AMJ 1972 – FMA 1973
2.1
AMJ 1973 – JJA 1974
-2.0
ASO 1976 – JFM 1977
0.8
ASO 1974 – AMJ 1976
-1.8
ASO 1977 - DJF 1977/78
0.8
ASO 1983 – DJF 1983/84
-0.9
AMJ 1982 – MJJ 1983
2.3
SON 1984 – MJJ 1985
-1.1
JAS 1986 – JFM 1988
1.6
AMJ 1988 – AMJ 1989
-1.9
AMJ 1991 – MJJ 1992
1.8
ASO 1995 – FMA 1996
-0.8
FMA 1993 – JJA 1993
0.8
JJA 1998 – MJJ 2000
-1.6
MAM 1994 – FMA 1995
1.3
SON 2000 – JFM 2001
-0.7
AMJ 1997 – MAM 1998
AMJ 2002 – FMA 2003
JJA 2004 – JFM 2005
2.5
1.5
0.9
NOAA Procedures for Issuing
Watches, Warnings and Advisories
Hurricanes/ Tropical
Storms
Tornadoes
Northeast Snowstorms
El Niño/ La Niña
Detection
Aircraft, satellites
Doppler radar, spotters
Satellites, conventional surface and
upper-air meteorological observations
Satellites, NOAA/TAO buoys, ship
observations, drifting buoys,
conventional surface and upper-air
meteorological observations
Watches
Hurricane/ Tropical Storm
conditions are possible
within 36 hours
Conditions are favorable for
tornadoes to develop within
the next 6 hours
Conditions are favorable for hazardous
winter weather conditions (e.g. snowfall,
ice accumulation, wind chill) within the
next 36 hours
El Niño / La Niña conditions are
possible within the next 3 months
Advisories
________
________
Issued for winter weather situations that
cause significant inconveniences, but do
not meet warning criteria
El Niño/ La Niña conditions are
observed and expected to continue
Warnings
Hurricane/ Tropical Storm
conditions are expected
within 24 hours
A tornado has been
observed, or is expected
soon
Issued when one or more types of
hazardous winter weather is occurring or
imminent
________
Low-level winds
measured by aircraft, or
cloud signature observed
by satellites used to
classify the intensity using
Saffir-Simpson Scale
(Simpson1974)
Assessment team evaluates
damage after an event and
then classifies the intensity
using the Fujita Scale
(Fujita 1971)
Assessment of the area affected, the
amount of snow, and the number of
people living in the path of the storm
using the Northeast Snowfall Impact Scale
(NESIS) (Kocin and Uccellini 2004)
Three month running mean values of
standardized SST departures in the
Niño 3.4 region, are used to classify
the intensity using the ENSO
Intensity Scale (EIS)
(Kousky and Higgins 2006)
Classification
of Intensity
Experimental Testing
of the ENSO Alert System
in CPC Forecast Operations
“Guidelines” for Issuing
Watches and Advisories
To
Outlook calls for a
transition
from
(or persistence of)
El Niño
Neutral
La Niña
El Niño
EA
FEA
LW
Neutral
EW
--
LW
La Niña
EW
FLA
LA
EA: El Niño Advisory
LA: La Niña Advisory
EW: El Niño Watch
LW: La Niña Watch
FEA: Final El Niño Advisory
FLA: Final La Niño Advisory
"Watches" are issued when a transition to El Niño or La Niña conditions is
anticipated within the next 3 months.
"Advisories" are issued when El Niño or La Niña conditions are observed and
expected to continue.
“Final Advisories” are issued after El Niño or La Niña conditions have ended.
•
ENSOENSO
Forecasters Forecasters
Template for the monthly
ENSO Diagnostics
Discussion
Template
for
the
Discussion
PutMonthly
an "X" in the boxENSO
where you feelDiagnostics
there is a greater than 50%
chanceprobability of El Nino (E)/ Neutral (N)/ La
Forecasters: Michelle/Gerry/Arun
E
Aug
Sept
Oct
Nov
JAS
ASO
SON
OND
N
X
L
X
X
X
“ X “ implies a
greater than 50%
chance of
El Niño (E),
Neutral (N), or
La Niña (L)
X
X
X
• Forecaster consensus is used for the ENSO Outlook “Synopsis Statement” in the EDD.
• The format of the Synopsis Statement varies, but it includes the following information:
- Current ENSO State;
- Anticipated Future ENSO State (usually within the next 3-6 months);
- Whether an ENSO state is expected to persist or whether a transition is anticipated.
• The Synopsis Statement informs the decision whether to issue a Watch or Advisory.
Verification
Subjective Verification
122 “Forecasts” from June 1997 – July 2007
80 correct forecasts/42 incorrect (66% correct)
Total
Correct
Wrong
% Correct
Conditions when forecast made:
La Niña
Neutral
El Nino
33
51
38
28
26
28
5
25
10
85%
51%
74%
• The ENSO Alert Status is verified against the ONI value for the next season
• A poster at the 32nd Climate Diagnostics and Prediction Workshop will include verification
for the preceding ~8 years
ENSO Intensity Scale
ENSO Intensity Scale (EIS) Class
Range of standardized ONI x 2.0
W5
+4.0 and greater
W4
+3.0 to +3.9
W3
+2.0 to +2.9
W2
+1.0 to +1.9
W1
+0.0 to +0.9
C1
-0.1 to -0.9
C2
-1.0 to -1.9
C3
-2.0 to -2.9
C4
-3.0 to -3.9
C5
-4.0 and less
• A simple five-class intensity scale for assessments of warm and cold phases of the ENSO cycle.
• EIS values obtained by doubling the standardized ONI values [ONI divided by the standard
deviation] for each overlapping three-month period and using the ranges specified in the Table.
• The use of the standardized ONI, rather than the ONI itself, results in reduced seasonality in the
distribution of values in the various EIS classes.
Number of Events in EIS Class by Season
EIS Class
DJF
JFM
FMA
MAM
AMJ
MJJ
JJA
JAS
ASO SON OND
NDJ
W5
1
2
2
1
0
1
2
2
1
1
1
1
W4
3
1
1
2
3
1
0
2
4
2
2
2
W3
4
5
4
4
4
7
6
6
1
3
6
6
W2
7
5
6
10
10
9
9
5
11
11
9
8
W1
12
16
14
11
11
9
14
11
5
5
6
7
C1
11
10
11
9
9
10
7
14
16
15
14
13
C2
10
10
8
8
8
9
8
5
10
11
12
13
C3
6
5
7
8
8
7
8
9
5
4
3
4
C4
2
2
3
2
2
3
2
2
3
4
3
2
C5
0
0
0
1
1
0
0
0
0
0
0
0
• For the period 1950-2005, the total number of seasons falling in the ranges W2-W5, W1-C1 and
C2-C5 are 194 (28.9%), 260 (38.7%) and 218 (32.4%), respectively.
• In most cases, global ENSO effects vary considerably for weak episodes (i.e. episodes with
small EIS values) and become greater and more consistent from event-to-event for strong
episodes (larger values of the EIS).
Summary
• An ENSO Alert System that includes Watches, Advisories, and a five-class ENSO Intensity Scale
(EIS) for warm & cold phases of the cycle was introduced.
• The ENSO Alert System is currently being tested in CPC Forecast Operations. An Official
Release is anticipated during FY09.
• CPC's monthly Climate Diagnostics Bulletin and ENSO Diagnostic Discussion will serve as the
primary vehicles for disseminating real-time information concerning the ENSO Alert Status to the
scientific community and public at large.
Back-up Slides
Overview
• An objective method that relates the ENSO Intensity Scale to impacts is introduced to improve
operational assessments of El Niño and La Niña impacts (analogous to what is done for hurricane
and tornado damage assessments using the Saffir-Simpson and Fujita scales, respectively).
• The method is illustrated by relating the EIS to precipitation anomalies in the global Tropics and
over the US.
• The methodology relating the ENSO cycle to impacts is quite general and can be used for other
types of impacts.
Operational Assessments and
the Tropical Precipitation Index (TPI)
•
• Introduce an objective method for operational retrospective assessments that
relates the EIS to effects.
 The EIS is not prescriptive concerning ENSO-related impacts, which are both positive and
negative (Note: different from tornadoes & hurricanes which have generally negative impacts).
• Illustrate the method using a Tropical Precipitation Index (TPI)
 Quantifies the departure from average in the global Tropics and Subtropics.
 Developed from monthly satellite-gauge merged precip (CAMS-OPI) (Janowiak and Xie 99).
 Defined as the 3-month running mean sum of the fractional area of the global Tropics and
subtropics (30°S-30°N) with precip anomalies above the 70th %ile and below the 30th %ile.
 Accounts for positive and negative precipitation departures from average on the tails of the
distribution. Percentiles are based on the gamma distribution.
 Base period: (1979-1995)
Evolution of the ONI and TPI
Global Tropics
(30S-30N)
•
Smallest (largest) values of TPI occur during NH summer (during major El Niño episodes).
•
During strong El Niño episodes (1982/83 and 1997/98) the global tropics are dominated by
negative precipitation anomalies over Indonesia (suppressed Austral-Asian monsoon).
•
During strong La Niña episodes (e.g. 1999-2001) the opposite is generally true.
Seasonal Timeseries of Areal Coverage of
Precip Anom for the US (<30thor >70th %ile)
•
Relatively wet (dry) conditions during El Niño (La Niña).
•
For the period shown, La Niña episodes appear to have a more detrimental impact on the U.S.
precipitation pattern than El Niño episodes.
COMPOSITES OF JFM PRECIPITATION
DEPARTURES (mm) BY EIS CLASS
•
Several features usually
ascribed to the extreme
phases of the ENSO cycle
are evident
•
There are some interesting
variations in the patterns
over northern California
and western Oregon and
western Washington that
probably deserve further
study.