Rapidly Evolving Cirrus Clouds Modulated by Convectively Generated Gravity Waves

Cirrus clouds can strongly affect Earth's radiation balance, but questions remain about their growth mechanisms and rates. Here we show that gravity (buoyancy) waves generated by a storm in Northern Australia on 13 November 2015 caused an observable rippling effect on cirrus clouds up to 1,000km away, as seen by the recently launched Himawari-8/9 geostationary satellite. Regional model simulations reproduce the propagation speed of the wave, which agrees with theoretical predictions, and show that the wave amplitude and timing near the tropopause can account for the cirrus modulation. The observed cirrus reach peak optical depths of order 0.3-1.0 and appear roughly in phase with the arrival of the relative humidity maximum, providing new evidence that cirrus clouds can respond rapidly (<30min) to environmental lifting. Moreover, the edge of a thick anvil cloud attached to the storm itself is observed to expand at the same speed as the wave, showing that the lifting mechanism can also apply to optically thicker ice clouds close to convective centers.