Tops of convective storms, namely when viewed in detail, belong among the most variable, fastest evolving objects we can observe in the satellite imagery. This is so because of the hectic activity of the overshooting tops, which in turn influences all other storm-top features. Given their typical lifetime, ranging somewhere between 5 to 20 minutes, the standard 15-minute full disk scanning period of the MSG satellites may be rather too long to capture all the details of storm top processes. An example of rapid evolution of the storm top is shown in the next image, Figure 16. It shows the storm above Nigeria, which we have seen already several times in previous parts of this material, and documents its evolution within one hour, in four consecutive MSG scans:
For a full size view, click on the image
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| Figure 16. Evolution of the storm from 2013-05-18 above Nigeria, shown in color-enhanced IR10.8-BT (190K-230K) images, within one hour interval, in four consecutive MSG full disk scans. |
As can be seen from this mosaic, within the 15 minute intervals some of the overshooting tops decay and new ones evolve, affecting, among others, the appearance of the cold plume-like feature which stretches from the southernmost overshooting top to the northeast. This typical period of overshooting tops was among many other reasons why EUMETSAT has decided to shorten the full disk scan period from 15 to 10 minutes for the Meteosat Third Generation (MTG) satellites. The shorter period will make it easier to see the evolution of storm tops in finer temporal resolution.
In the the loops below you can follow the evolution of the storm above within the same period, in the same IR10.8-BT color-enhanced product, and in the HRV band (the same period):
IR10.8-BT (190-230K) loop
HRV loop
When monitoring convective storms using the satellite imagery, we should always keep in mind the possible big temporal variability of storm tops, and be aware that between two consecutive 15 minute scans a lot can happen. Therefore an absence of "typical" possible storm-severity indicators, such as distinct overshooting tops, cold rings or cold-U/Vs, increased cloud-top microphysical reflectivity, and many other (for a more complex overview of these please refer e.g. here and here) does not necessarily mean that the storm is not or will not become severe - these features can evolve very fast, together with the storm gaining in strength. For these reasons, if the satellite imagery is the only (or prime) real-time remote sensing source of weather information (namely in large areas lacking weather radars), forecasters should follow these continuously, paying attention to every new image scan, every new processed image product.
A footnote (instead of an exercise):
As scientists involved in the research of tops of convective storms were curious to see what will be the variability of storm top features as seen at even shorter scan period, EUMETSAT has conducted several experiments in 2012 and 2013, using the present MSG satellites reconfigured to acquire data at 2.5-minute rapid scan mode. Several examples (movie files in various bands and products). The most interesting cases, together with a related presentation can be downloaded from here: http://essl.org/cwg/?p=417. Detailed examination of these very short period scan images shows that even in these we can find very transient storm top features, some of which can be traced in one single image only. This implies that some of the overshooting tops can live for even less than 5 minutes, which makes their detection in 15-minute regular data rather a random issue ...
If you have any comments or questions please add them in the box below.
A footnote (instead of an exercise):
As scientists involved in the research of tops of convective storms were curious to see what will be the variability of storm top features as seen at even shorter scan period, EUMETSAT has conducted several experiments in 2012 and 2013, using the present MSG satellites reconfigured to acquire data at 2.5-minute rapid scan mode. Several examples (movie files in various bands and products). The most interesting cases, together with a related presentation can be downloaded from here: http://essl.org/cwg/?p=417. Detailed examination of these very short period scan images shows that even in these we can find very transient storm top features, some of which can be traced in one single image only. This implies that some of the overshooting tops can live for even less than 5 minutes, which makes their detection in 15-minute regular data rather a random issue ...
If you have any comments or questions please add them in the box below.
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