IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4P1_3E-O17

Room A1

Date/Time: July 24 15:30-15:45

Meteorological interactions with volcanic plumes in the moist tropics: implications forvolcanic plume monitoring
Andrew Tupper
Bureau of Meteorology, Australia
E-mail: a.tupper@bom.gov.au

The development of the International Airways Volcano Watch in the early 1990s created an operational requirement
for real time global monitoring for volcanic ash at all observable concentrations (more recently formalised as visible
or discernable ash through the work of the International Volcanic Ash Task Force). One of the more interestingareas of the world to do that has been the moist tropics, with many active volcanoes, relatively poor seismic
monitoring, and a highly active atmosphere dominated by deep convection.

The frequency of showers and thunderstorms (particularly around volcanoes and other mountains), poor
observing conditions on the ground, satellite obscuration by long-lasting cirrus anvils, and challenges in funding
and maintaining ground based infrastructure such as radar and lidar together mean that the occurrence andheights of volcanic plumes have certainly been under observed in the moist tropics. Volcanic Ash Advisory Centre
data also demonstrates a strong observational bias towards the drier seasons. As a result, even large eruption
plumes such as from the 2010 eruptions of Merapi in Indonesia can be very difficult to monitor.

In addition, within a moist tropical environment there is an active interplay between active volcanoes andthe meteorological environment. In an unstable or potentially unstable environment, tropical convection to highaltitudes (17+ km) is frequently triggered by very subtle influences such as low level sea breezes or differential
heating. Modelling suggests and observations demonstrate that active volcanoes, with a range of influences
extending to the very unsubtle, can act as triggers to produce volcanic cumulonimbus such as those observed atPinatubo, or volcanic plumes that have been very significantly increased in height and in ice content through moist
convective processes. Eruption heights tend to cluster near the height of the tropical tropopause; relatively weak
volcanic eruptions can trigger deep tropospheric convection that transports volcanic material to the tropopause orabove. Because of the role of hydrometeors in enhancing particle aggregation and removal, the smaller modelled
eruptions also produce a relatively small proportion of fine ash in the umbrella cloud compared to eruptions in adry atmosphere.

It is therefore difficult to reliably infer the strength of a tropospheric or lower stratospheric volcanic plume in
the moist tropics using its reported height alone. Additional volcanological and meteorological observations,
including seismic, visual, lidar and radar observations, and geostationary remote sensing can be added to satellite
height observations to assist in rapidly assessing eruption magnitude and the real-time response required.
Close collaboration between the volcanological and meteorological science communities will help to attain these
additional observations on a routine, operational basis.

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