Section 3.1Linear disturbances are synoptic systems that have concentrated or discontinuous kinematic parameters, such as horizontal deformation, wind shear, vorticity, convergence, or confluence, along zones or lines whose length is much longer than width. Air masses in the tropics are much more homogeneous than those in the mid-latitudes. It is therefore almost impossible to define a surface front in the tropics according to the polar- front definition, which requires a zero order discontinuity of surface pressure, pressure tendency, wind speed and direction, temperature, moisture, cloud types, and current weather. Since the vertical stratification of oceanic tropical air is usually conditionally unstable, the lower tropospheric cyclonic shear lines or convergence lines are frequently associated with organized deep convection. These linear disturbances are also called squall lines or sea breeze fronts. Two well-studied tropical linear disturbances are the squall lines of West Africa and Sumatra of Indonesia.
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Chapter 2