Thermally generated convection and precipitation over volcanoes: Numerical modelling of flow over Montserrat

Atmospheric flow over orography is a classic research area, while the atmospheric response to surface heating has become a focus more recently in the context of solar heating and forest fires. Here, for the first time, these forcing mechanisms are superposed to examine atmospheric flow over a mountain with a heated summit, i.e. an active volcano. Intense rainfall over active volcanoes is known to trigger dangerous volcanic hazards, from remobilising loose surface material into lahars or mudflows, to initiating explosive activity such as pyroclastic flows. The effect of a heated volcanic surface on the atmospheric circulation is investigated here – including examining the triggering of precipitation over the volcano. Recent activity at the Soufri`ere Hills Volcano (SHV), Montserrat, Eastern Caribbean, is a well-documented example of such rainfall–volcano interactions. Hence, Montserrat is used as a template for the experiments, although the experimental setup is general so the results will have applicability for other tropical island volcanoes. The Weather Research and Forecasting (WRF) atmospheric model has been used for the study, run in an idealised configuration with horizontal grid sizes down to 100 m. Initially, the effect of the heated surface is studied through idealised simulations over a Gaussian mountain with an imposed surface temperature anomaly on the volcano summit. Subsequently, a digital elevation model (DEM) of Montserrat is used to study the effects over this specific island. The atmospheric structure in most simulations is that of a typical tropical setting – easterly TradeWinds, capped by a temperature inversion. In these cases, localised convection triggered by the heat source can overcome convective inhibition and force deep convection, if there is sufficient convective available potential energy. A significant increase in precipitation over the volcano covering a 4 km2 area is consistently simulated for surface temperature anomalies above 40�C, an area-average value that is exceeded at the SHV. For a range of realistic atmospheric conditions, covering up to 18% of days in a relevant climatological study in the Caribbean, the precipitation increase is well above the observed threshold (5–10 mm hr

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Poulidis, Alexandros-Panagiotis

Language dc:language

en