Basic appearance of convective storms

The first important thing to keep in mind is that operational weather satellites with their passive sensors (such as SEVIRI, AVHRR, MODIS or VIIRS) observe cloud tops of convective storms only, they do not see the internal structure of storms. They are not capable of detecting and monitoring the "real weather" under the cloud. Any still image from a polar-orbiting satellite shows the storm's appearance at the given instant of time, when the image was taken (scanned) by the satellite. Such a "snapshot" does not show evolution of the storm, but still can be considered as a specific "record" of the previous storm activity which formed the cloud. Thus, a much better tool to observe convective storms are geostationary satellites, which are able to monitor and document the storm evolution since its formation, through the mature stage of the storm, till its weakening and final dissipation.

The appearance of convective storms as seen from above, as captured by the weather satellites, depends on many factors. The most important among these are the internal storm dynamics (namely the updraft strength), interaction of the storm with its environment (namely with the storm-relative winds), but also the viewing geometry, and of course the spectral band(s) we use to display the storm.

The updraft strength and its duration are among the most important factors which determine the overall storm appearance. Satellite imagery provides an indication of this strength and duration from:
 - the total anvil area, speed of the anvil growth, the cloud-top microphysics, and presence of some specific cloud-top features typical for strong updrafts - such as distinct overshooting tops, gravity waves spreading out from the storm cores, IR features known as cold-U/V or cold-ring with their embedded warm areas, above-anvil ice plumes, and several others. In general, the stronger the updraft, the more dynamic are the changes at the storm-top levels, and usually we can also observe more of the updraft-related features as listed above together, or the more distinct and complex these are. We will get back to some of these features later on. For now let's focus on influence of some of the other factors - the viewing geometry and interaction of the storm with its environment. Images in this first part are mostly shown here in their most simple, basic black-and-white enhancement. The advantage of using more sophisticated methods of enhancement will be discussed later.