# Presentation: 929631

## Discrepancies Between Satellite Detection and Forecast Model Results of Ash Cloud Transport: Case Study of the 2001 Eruption of Mt. Cleveland Volcano, Alaska

**Discrepancies Between Satellite Detection and Forecast Model Results of Ash Cloud Transport: ****Case Study of the 2001 Eruption of Mt. Cleveland Volcano, Alaska**

- David Schneider, USGS-Alaska Volcano Observatory
- Rene Servranckx, Environment Canada, Montreal VAAC
- Jeff Osiensky, National Weather Service, Anchorage VAAC

## Motivation/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 Map

-  R. Wessels

**Cleveland Volcano**

**Anchorage**

-  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 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 Map

## Ash 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 Detection

_**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 

- 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 UTC

**Notes:**
A thermal anomaly and a cold cloud are a good bet that there is an eruption. Does is contain ash?

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

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

**Notes:**
This first image starts to show shear in the cloud. Cloud is elongated for about 100 km or 50 nautical miles NW and SE

## AVHRR Band 4: 2/19/01 1645 UTC

**Notes:**
Cloud height is the next thing to get. Compare temperature to Cold Bay radiosonde. This may not be entirely representative, but a good rule of thumb in the North Pacific is that any cloud with a temperature of –50 C or colder is a problem for enroute aviation.

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

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

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

## 2000 UTC: 2/19/01 E + 5 hours

**2000 UTC: 2/19/01**** E + 5 hours**

## 2200 UTC: 2/19/01 E + 7 hours

**2200 UTC: 2/19/01**** E + 7 hours**

## 0000 UTC: 2/20/01 E + 9 hours

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

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

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

**Upper Level Cloud >FL300**

**Lower Level Cloud <FL200**

**Notes:**
This first image starts to show shear in the cloud. Cloud is elongated for about 100 km or 50 nautical miles NW and SE

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

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

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

## 2000 UTC: 2/19/01 E + 5 hours

**SIGMET Covers this area at 2 levels**
**Supported by PIREP**

**Upper Level Cloud Appears in BTD Images**

## 2200 UTC: 2/19/01 E + 7 hours

**Lower Level Cloud Starts to “Fade” in BTD Images**

## 0000 UTC: 2/20/01 E + 9 hours

## 0000 UTC: 2/20/01E + 9 hours

**0000 UTC: 2/20/01****E + 9 hours**

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

- FL360: “Ash and sulfur odor in cockpit”

- FL360: “Cinders and sulfur odor in cockpit”

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

**SIGMET extended to cover cloud <FL400**

## 0400 UTC: 2/20/01 E +13 hours

## 0600 UTC: 2/20/01 E +15 hours

**SIGMET “uses” more model guidance**

## 0600 UTC: 2/20/01E + 15 hours

- FL S-200

**0600 UTC: 2/20/01****E + 15 hours**

## 0800 UTC: 2/20/01 E +17 hours

## 1000 UTC: 2/20/01 E + 19 hours

## 1200 UTC: 2/20/01 E + 21 hours

## 1200 UTC: 2/20/01E + 21 hours

- FL S-200

**1200 UTC: 2/20/01****E + 21 hours**

## 1400 UTC: 2/20/01 E + 23 hours

## 1600 UTC: 2/20/01 E + 25 hours

## 1800 UTC: 2/20/01 E + 27 hours

**As signal starts to fade, the SIGMETs give satellite images more “weight”.**

## 1800 UTC: 2/20/01E + 27 hours

**1800 UTC: 2/20/01****E + 27 hours**

## 2000 UTC: 2/20/01 E + 29 hours

## 2200 UTC: 2/20/01 E + 31 hours

## 0000 UTC: 2/21/01 E + 33 hours

## 0000 UTC: 2/21/01 E + 33 hours

**0000 UTC: 2/21/01**** E + 33 hours**

## 0200 UTC: 2/21/01 E +35 hours

## 0400 UTC: 2/21/01 E +37 hours

## 0600 UTC: 2/21/01 E +39 hours

## 0600 UTC: 2/21/01 E +39 hours

**0600 UTC: 2/21/01**** E +39 hours**

## 0800 UTC: 2/21/01 E +41 hours

## 1000 UTC: 2/21/01 E +43 hours

## 1200 UTC: 2/21/01 E +45 hours

## 1200 UTC: 2/21/01 E +45 hours

**1200 UTC: 2/21/01**** E +45 hours**

## 1400 UTC: 2/21/01 E +47 hours

## 1600 UTC: 2/21/01 E +49 hours

**SIGMET HOTEL 12 cancelled at 1715 UTC on 2/21/01**

## 1800 UTC: 2/21/01E + 51 hours

## 0000 UTC: 2/22/01E + 57 hours

## 0600 UTC: 2/22/01E + 63 hours

## 1200 UTC: 2/22/01E + 69 hours

- _2/22/01 at 1408 UTC_
- FL360: “Particles and strong odor in cockpit”

## 1800 UTC: 2/22/01E + 75 hours

## Final Thoughts

- With satellite images, does an absence of detectable ash mean that ash is absent?
- Does the prediction of ash in a dispersion model mean that ash is present?
- The eruption response demonstrates how the balance between data sets can evolve.
- Cloud height is crucial but hard to determine.
- No reports of damage to aircraft. Does this mean that no damage occurred?
- Was the decision to end warnings after 48 hours prudent given a report of odor 24 hours later? (Zero tolerance?)

## Thank You

## Composite Ash Movement

**Image by K. Papp**

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

## 0000 UTC: 2/20/01E + 9 hours

## 0600 UTC: 2/20/01E + 15 hours

## 1200 UTC: 2/20/01E + 21 hours

- FL S-200

## 1800 UTC: 2/20/01E + 27 hours

## 0000 UTC: 2/21/01 E + 33 hours

## 0600 UTC: 2/21/01 E +39 hours

## 1200 UTC: 2/21/01 E +45 hours

**Last GOES detection was at 1600 UTC on 2/21/01.**

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

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