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ATS/ESS 452: Synoptic Meteorology Wednesday 09/10/2014

ATS/ESS 452: Synoptic Meteorology Wednesday 09/10/2014. Quiz! (Short?) Weather Discussion Continue Review Material Geostrophic Wind Continuity Vorticity. Synoptic Scale Governing Equations. Frames of reference:

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ATS/ESS 452: Synoptic Meteorology Wednesday 09/10/2014

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  1. ATS/ESS 452: Synoptic Meteorology Wednesday 09/10/2014 • Quiz! • (Short?) Weather Discussion • Continue Review Material • Geostrophic Wind • Continuity • Vorticity

  2. Synoptic Scale Governing Equations • Frames of reference: • Eulerian – object is fixed in space; it doesn’t move; changes due to air moving through the object; Referred to as the local derivative in equations • Lagrangian – object is allowed to move with the air; Referred to as the total derivative in equations • What is cold air advection (CAA)? What is warm air advection (WAA)? • Cold air advection is the process in which the wind blows from a region of cold air to a region of warmer air • Warm air advection is the process in which the wind blows from a region of warm air to a region of cooler air

  3. CAA WAA

  4. Temperature Advection

  5. Geostrophic Wind • **A scale analysis of the *horizontal* governing equations reveals that only the pressure gradient force and Coriolis are important on the synoptic scale • The resulting balance between these terms is called geostrophic balance, which yields the geostrophic wind • **At the synoptic scale, in the Northern hemisphere, the geostrophic wind blows parallel to isobars (isoheights) with low pressure (low heights) to the left. • Geostrophic balance allows the governing equations to be simplified considerably and allows the development of quasi-geostrophic theory (chapter 2)

  6. Notice how wind in this 500mb map is flowing west to east, generally paralleling the isoheights geostrophic balance

  7. Geostrophic balance does not always apply  surface

  8. Vertical Momentum Equation • Which terms are left if you perform a scale analysis on this equation? • All that remain are the vertical PGF and gravity. • The balance between these two terms is called hydrostatic balance. • **Synoptic scale motions are largely in hydrostatic balance in the vertical direction • If we are to assume hydrostatic balance, then are we assuming no vertical air motion (i.e. no vertical acceleration)? • NO… they’re just very small compared to the vertical PGF and gravity Vertical PGF Vertical acceleration friction Coriolis gravity

  9. Continuity Equation • This relation is based on the conservation of mass (in a closed system, mass will not change). • The kinematic method uses the continuity equation to estimate vertical motion • Not very accurate • Errors in actual wind observations will lead to very large errors in the vertical motion estimate • Convergence of winds at the surface leads to vertical motion • What do you think convergence aloft leads to? Divergence of winds aloft? • (sinking air) (rising air) • Being able to correctly diagnose and forecast divergence and convergence aloft is an important component of this course

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