getting to grips with surveillance(133)

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A super cell thunderstorm can grow up to 10 NM horizontally and 60 000 ft vertically. Due to the powerful updraft, the top of the thunderstorm may deploy above the Tropopause (step 3 of Figure G - 2).
The resulting anvil top deploys downwind and commonly produces hail. It can produce powerful updraft (more than 90 kt – 9 100 ft/min), surface winds (more than 70 kt), large hailstones (10 cm – 4 in), and tornadoes.
G.2.5. OCEANIC CELL
Oceanic cells contain less water than continental cells. Consequently, for equivalent height, oceanic cells are less massive and less reflective than continental cells.
G.2.6. SQUALL LINE
A squall line is a line of thunderstorms that form approximately 150 NM ahead of a cold front. It may extend on several hundred miles. Typical thunderstorm weather (heavy rain, hail, lightning, strong winds, tornadoes) may occur on a large area.

G.3. HAIL ENCOUNTER

Figure G - 3 provides a rough order of magnitude of hail encounter probability with a mature thunderstorm. The probabilities may vary according to the current weather conditions.
The thunderstorm is vertically split into three thirds:
- The top third (ice crystals only) and the mid third present a high probability of hail encounter,
Figure G - 3: Probability of hail encounter
- The bottom third is the area of medium probability.
Hail may also be encountered on the downwind side. This is the reason why aircraft should avoid thunderstorm on the upwind side.
G.4. TURBULENCE
The present paragraph briefly references the different kind of turbulence.
G.4.1. CLEAR AIR TURBULENCE (CAT)
CATs occur at any altitudes:
- At high altitudes in the shear of jet streams, or
- Any altitudes downstream of mountains, or
-Near areas with high vertical wind gradient.
Weather radars do not detect CATs because CATs do not contain water.

G.4.2. TURBULENCE DOME
Several thousand feet above the visible top of a thunderstorm, severe turbulence occurs.
G.4.3. THUNDERSTORM VAULT
The thunderstorm vault occurs when the airmass is unstable at high level only and the lower air is too dry to feed the convection. Most of the unstability is trapped in the upper part of the thunderstorm. Consequently, there are very little precipitations. Contrary to a common thunderstorm structure, the bottom part of the thunderstorm is less reflective than the upper part, or even not visible on radar display. Refer to Figure 6-27.
G.4.4. DOWNDRAFT
The downdraft is a movement of cool air induced by the precipitation of water droplets. When the downdraft hits the ground, it spreads out in all directions.

If the thunderstorm is stationary, the resulting gust front will be more or less circular, centered on the downdraft.
If the thunderstorm moves, the resulting gust front precedes the thunderstorm: the gust front is downwind.
　
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