discrepancies between satellite detection and forecast model results of ash cloud transport: case...

Discrepancies Between Discrepancies Between Satellite Detection and Satellite Detection and Forecast Model Results Forecast Model Results of Ash Cloud Transport: of Ash Cloud Transport:

Case Study of the 2001 Case Study of the 2001 Eruption of Mt. Cleveland Eruption of Mt. Cleveland Volcano, AlaskaVolcano, Alaska

David Schneider, USGS-Alaska Volcano ObservatoryDavid Schneider, USGS-Alaska Volcano Observatory

Rene Servranckx, Environment Canada, Montreal VAACRene Servranckx, Environment Canada, Montreal VAAC

Jeff Osiensky, National Weather Service, Anchorage VAACJeff Osiensky, National Weather Service, Anchorage VAAC

Motivation/BackgroundMotivation/Background

• The understanding that total avoidance of ash clouds is required but confusion about what is meant by (or how to achieve) “zero tolerance”.

• A realization that operational decisions typically involve resolving conflicts between data sources.

• How should warnings and info releases utilize model results, satellite data, and observer reports? What is the proper “weight” to give each when they are in conflict?

• The question of how long to keep a warning going

• A look at the 1991 eruption of Cleveland volcano will illustrate these issues, but not answer any of these questions.

Location MapLocation Map

R. Wessels

Cleveland VolcanoCleveland Volcano

AnchorageAnchorage

• About 900 miles from Anchorage; 5675 ft high.

• Eruption in 2001 is the largest from a seismically unmonitored volcano since the formation of AVO in 1988.

Summary of February 19 EruptionSummary of February 19 Eruption• Eruption detected in AVHHR satellite image as part of

routine monitoring by an AVO remote sensing analyst, about 3 hours after the eruption start.

• Ash production for about 6 hours, and detected in GOES satellite images for 48 hours.

• No Color Code issued by AVO for Cleveland because of the lack of a seismic monitoring network (policy since changed).

• Combined response of 3 VAACS (Anchorage, Washington, and Montreal), Anchorage Center Weather, and the AVO. Pointed out a need for additional tools to facilitate collaboration (VACT).

VAAC MapVAAC Map

Ash Cloud Forecast ModelsAsh Cloud Forecast Models

• A number of models used by responding groups

• PUFF: Anchorage VAAC and AVO• Canerm: Montreal VAAC• Vaftad: Washington VAAC

• Although there are differences between the models, they are typically in general agreement.

• Ash particles are essentially tracers of flow in the atmosphere, and output is influenced by a number of factors. The ash is predicted, not detected.

Satellite-based Ash Cloud DetectionSatellite-based Ash Cloud Detection

AVHRR Band 4

-60 Degrees C 50AVHRR Band 4m5

-5 Degrees C 5

Split-window method is a common technique: Brightness temperature difference (BTD) between 2 thermal infrared channels

Semitransparent volcanic clouds generally have negative BTDs while meteorological clouds generally have positive BTDS

Satellite-based Ash Detection Satellite-based Ash Detection

• The magnitude of the BTD signal depends upon many factors:– Cloud opacity (amounts of ash and water in the

cloud)

– Size and size distribution of the cloud particles

– Temperature contrast between the cloud and the surface beneath it

– Satellite viewing angle

– Atmospheric conditions

• Thus, the detection limit varies (+/-) between eruptions and during cloud transport.

AVHRR Band 3: 2/19/01 1645 UTCAVHRR Band 3: 2/19/01 1645 UTC

Thermal Anomaly

-55 50Degrees C

Cold Cloud

AVHRR Band 4m5: 2/19/01 1645 UTCAVHRR Band 4m5: 2/19/01 1645 UTC

-5 5Degrees C50 nm

i (100 km)


-55 10Degrees C

0

10000

20000

30000

40000

50000

60000

-60-50-40-30-20-100

Temperature (C)

Alt

itu

de

(ft)

-53.5 C-53.5 C

- 33 C- 33 C

1600 UTC: 2/19/011600 UTC: 2/19/01 E + 1 hour E + 1 hour

1800 UTC: 2/19/011800 UTC: 2/19/01 E + 3 hours E + 3 hours

0200 UTC: 2/20/010200 UTC: 2/20/01 E +11 hours E +11 hours

AVHRR Band 4m5: 2/19/01 1645 UTCAVHRR Band 4m5: 2/19/01 1645 UTC

-5 5Degrees C

Upper Level Upper Level Cloud >FL300Cloud >FL300

Lower Level Lower Level Cloud <FL200Cloud <FL200