Example: Thunderstorms and microbursts

CAPPI image of thunderstorm The radar observation of thunderstorms has been one of the first applications of weather radars because radar was the first instrument that allowed a complete view of the phenomenon at a good enough resolution. In this example, a complex cluster of thunderstorms (strong precipitation in red and pink, lighter rain in yellow and green) strike the Metropolitan Montreal area before heading north-east. A vertical cross-section of reflectivity (shown below) done through some of the cells reveal that they are particularly intense and extend to about 12 km at downpour intensity.

Additional cross-sections done in several cells show the presence of microbursts. Microbursts are strong wind currents going down often associated with thunderstorms and present a major threat to aviation. On radar, microbursts manifest themselves by a divergence signature near the surface (the air is seen to go away from a certain place). This is because the air that comes down cannot go further when it hits the ground and hence spreads in all directions. On Doppler images, it can be recognized by the presence of a couplet: velocities going towards the radar at a given range and immediately going away from the radar at a slightly larger range.

 

Cross-section of thunderstorm cells

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