Deep convective cloud phenomena in the upper troposphere/lower stratosphere—A new development in cloud science

Recent discoveries of a few new phenomena atop many Midlatitude deep convective storms open up a new area for cloud research. The elucidation of these phenomena will not only help unraveling the physical processes involved in them, but also understanding the impacts of deep convective clouds on the large-scale and global atmospheric processes. This paper will give a summary of these findings and their implications to other fields.

The first is the storm top plume phenomenon. This was first discovered by meteorological satellite images that reveal the existence of chimney plume-like clouds atop the anvils of some severe thunderstorms. The plumes are generally about 2-3 km above the anvils. Since the anvils in some of these storms are already at the tropopause level, the plumes are thus in the lower stratosphere. A numerical simulation of the plume formation using a 3-D nonhydrostatic storm model shows that the plumes derive their moisture from the storm below, which implies that there is a net mass transfer from the troposphere to the lower stratosphere. Obviously, tropospheric aerosol particles and trace gases can also be transported by this same mechanism. Videos of both satellite images and cloud model simulations will be shown to illustrate this phenomenon.

The second phenomenon is related to the jumping cirrus observed by Fujita in the 1980s. While it is well known that deep convective clouds can excite gravity waves, it was not understood previously that wave breaking occurs readily at the storm top. Cloud model simulation demonstrates clearly that the jumping cirrus is a cloud top wave breaking phenomenon with both horizontal and vertical speeds of ~ 10 m/s. Again, the jumping cirrus phenomenon is also related to the troposphere-to-stratosphere exchange. Ground-based video loops and cloud model animations will be shown to illustrate it.

The third is the formation of pyro-cumulonimbus (pyro-Cb) in areas affected by fire, often in high latitude locations (e.g., Alaska and Northern Canada). With the help of heat energy released by forest or prairie fires, storms form that often penetrate the local tropopause that send ashes through the tropopause to reach lower stratosphere. Satellite images and data analysis as well as model simulations will be shown

All these water vapor, aerosol particles and trace gases that penetrate through the tropopause can potentially interact strongly with the short and long wave radiation and hence influence the global climate process. They can also be involved in chemical reactions in the stratosphere and some of them (e.g., the formation of OH radical) are closely associated with ozone depletion. They may also affect the global chemical processes.

The properties of clouds associated with these phenomena are poorly understood. Potential research areas needed to understand these phenomena and their implications will be discussed.