GSNZ Wellington branch talk

The 15 January 2022 eruption of Hunga Tonga Hunga Ha’apai ( significantly impacted the Kingdom of Tonga as well as the wider Pacific region Additionally, much of the physical phenomena associated with the eruption were of a scale unparalleled in the era of human observation The eruption column attained a maximum height of 58 km whilst the umbrella cloud reached a diameter approaching 600 km within about 3 hours Also remarkable was the intensity of volcanic lightning generated during the eruption, with the Vaisala Global Lightning Database (GLD 360 recording over 300 000 strikes near HTHH over a two hour period We have combined satellite imagery with the spatiotemporal distribution of lightning strikes to constrain the dynamics of umbrella spreading The first lightning strikes occurred at 04 09 UTC, with lightning intensity peaking at approximately 5000 strikes per minute at 05 03 During this time, lightning was initially concentrated in a circle above HTHH, with an areal extent that grew with the observed eruption cloud However, by 04 27 radial structure appeared in the lightning spatial distribution, with strikes clustered both directly above HTHH and in an annulus of radius 50 km Comparison with satellite imagery shows that the radius of this annulus coincided with the umbrella cloud radius, and both grew to about 150 km by 04 47 From this time, the umbrella cloud growth rate decreased whilst the annulus itself contracted to a smaller radius of about 50 km again Radial structure in the spatial distribution of strikes persisted until about 05 37 after which lightning remained focused at smaller radii These observations have important implications for umbrella spreading dynamics, revealing internal flow properties and providing higher temporal resolution data than satellite imagery alone Consequently, our results provide important data for informing and validating numerical models of umbrella cloud spreading.

This talk will take place in person at Victoria University of Wellington and be live streamed https://vuw.zoom.us/j/98830912410

This talk is being hosted by the GSNZ Wellington branch wellington@gsnz.org.nz