An Alert Classification System for An Alert Classification System for Monitoring and Assessing the ENSO-CycleMonitoring 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 SystemENSO 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

La Niña

neutral

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 0.7

MAM 1957 – MJJ 1958 1.6

ASO 1949 – FMA 1951 -1.8

MAM 1954 – DJF 1956/57 -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 2.5

AMJ 2002 – FMA 2003 1.5

JJA 2004 – JFM 2005 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

________

Classification of Intensity

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)

Experimental Testing of the ENSO Alert SystemENSO Alert System

in CPC Forecast Operations

“Guidelines” for Issuing Watches and Advisories

To

El Niño Neutral La Niña

Outlook calls for atransition

from (or persistence of)

El Niño EA FEA LW

Neutral EW -- LW

La Niña EW FLA LA

EA: El Niño AdvisoryLA: La Niña AdvisoryEW: El Niño WatchLW: La Niña WatchFEA: Final El Niño AdvisoryFLA: 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. •

ENSO Forecasters Template for the Monthly ENSO Diagnostics Discussion

• 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.

“ X “ implies a greater than 50% chance of

El Niño (E), Neutral (N), or

La Niña (L)

Verification

• 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

Subjective Verification122 “Forecasts” from June 1997 – July 2007

80 correct forecasts/42 incorrect (66% correct)

Conditions when forecast made: La Niña Neutral El Nino

Total 33 51 38Correct 28 26 28 Wrong 5 25 10

% Correct 85% 51% 74%

ENSO Intensity Scale

• 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.

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

Number of Events in EIS Class by Season

• 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).

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

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

• 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.

Global Tropics(30S-30N)

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.