#2694 Postby TROPICALCYCLONEALERT » Wed Aug 10, 2022 9:52 pm
Lots of talk regarding wavebreaking and not enough people knowing what it is…
To put it simply, "wavebreaking" is part of the process of heat redistribution around the planet, particularly in the midlatitudes where deep, tropical thunderstorms don't really occur. Considering the fluidity of our atmosphere, this is essentially a constant and ongoing somewhere on the planet at all times. It has no start or stop which makes distinguishing individual events somewhat difficult.
Let's take the example of an upper-level trough crossing United States, slowly becoming negatively tilted as it approaches the eastern shoreline of the continent. Ahead of this trough, a strong jet streak creates a region of intense upper-level diffluent flow -- essentially a vacuum of sorts aloft that forces air in the column beneath to rise. As it rises, it expands in response to the lessened atmospheric pressure and cools as a result. This cooling converts the gaseous air parcel into a cloud; convection. As this airmass condenses, heat is released from the water molecules into the atmosphere, causing subtle but impactful warming. We often hear this part of the process referred to as "latent heat release", with the first two parts of the term indicating that this process has to do with condensation (or melting!). This warming causes the atmosphere to expand in that particular area, which means it takes up more space and is literally higher in a sense. This is represented by positive geopotential height anomalies or positive potential vorticity at that level. The trough --> ridge pattern I just described is the classic cyclonic wavebreak (CWB).
The opposite, a ridge --> trough pattern, forms the typical anticyclonic wavebreak pattern. The expanding upper-level ridge created by the CWB takes up space and must subside somewhere downwind. Usually, this subsidence causes compression aloft, thus lowering geopotential heights (and by extension, a tendency towards negative potential vorticity). While both forms of wavebreaking are omnipresent, anticyclonic wavebreaks arguably impact tropical cyclone activity more directly than their counterparts. In this particular scenario, midlatitude ridging becomes dominant over the North Atlantic. In response, wavebreaking intensifies equatorward as troughing is shunted south and possibly even cutoff from the jet stream. This process reinforces the tropical upper tropospheric trough, a climatological feature that stretches through most of the subtropical Atlantic, potentially strengthening it or impacting its placement. This on its own can lead to higher shear in area adjacent to the main development region, making it more difficult to sustain intense tropical cyclones for a long period of time. As troughs get forced into the subtropics, midlatitude dry air can also make its way down to regions where hurricanes are common posing an additional threat alongside the common Saharan Air Layer. Wavebreaking and these side-effects are common and are even expected most months of the year, including July and the first half of August. If it persists into September though, we might have a problem with regards to how active the season will end up being. With the MJO expected to cross Africa and the Indian Ocean towards the end of the month though, we may see this midlatitude activity let up somewhat.
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