ATSC Post-midterm LO 2 .pdf - Global Circulation - Part 1:...

Global Circulation - Part 1:
Description, Diff. Heating, Thermal Circulations, Geostrophic Adjustment, Thermal Wind
Learning Goals - Global Circulation
At the end of this section, you should be able to:
1. Use the global-circulation nomenclature and jargon (e.g., zonal, mereridional,
extratropical, etc.)
2. Describe and name the dominant horizontal general-circulation flow patterns at the
surface, including monsoonal flows.
Subtropical jet: Near 30° latitude in each hemisphere is a persistent belt of strong westerly
winds at the tropopause called the subtropical jet. This jet meanders north and south a bit.

Polar jet: In mid-latitudes at the tropopause is another belt of strong westerly winds called the
polar jet
Rossby wave: The centerline of the polar jet meanders north and south, resulting in a wave-like
shape called a Rossby wave (or planetary wave)
Troughs: The equatorward portions of the wave are known as low-pressure troughs
Ridges: poleward portions are known as high-pressure ridges
Hadley cells: Vertical circulations of warm rising air in the tropics and descending air in the
subtropics. At the bottom of the Hadley cell are the trade winds. At the top, near the tropopause,
are divergent winds. The updraft portion of the Hadley circulation often contains thunderstorms
and heavy precipitation at the ITCZ. This vigorous convection in the troposphere causes a high
tropopause (15 - 18 km altitude) and a belt of heavy rain in the tropics.
Ferrel cell: When averaged around latitude bands, the net effect is a weak vertical circulation
Monsoon Circulations: continental-scale circulations driven by continent-ocean temperature
contrasts. In winter, low-pressure centers are over the cool oceans, and high-pressure centers are
over the colder continents. These monsoon circulations represent average conditions over a
season. The actual weather on any given day can be variable and can deviate from these seasonal
averages. Our Earth has a complex arrangement of continents and oceans. As a result,
seasonally-varying monsoonal circulations are superimposed on the seasonally-varying planetary
scale circulation to yield a complex and varying global-circulation pattern.