OVERVIEW:

We will discuss the concept of mathematical "slope" and its algebraic approximation; the cause and manifestations of horizontal temperature and pressure gradients; the geostrophic wind approximation (from coriolis and pressure gradient); cyclonic and anti-cyclonic curvature; cyclostrophic circulation (from centripetal acceleration and pressure gradient); and the influence of friction.

OUTLINE:

1. Slope: Instantaneous and approximate.

1.1. Definition and importance of scalar gradients.

1.2. Method of estimation (algebraic and graphical).

2.1. Forcing: Uneven heating of the Earth's surface. Curvature of the Earth and the tilt of the Earth's axis causes sunlight (incoming energy) to be unevenly distributed over the planet surface.

2.2. Result: Uneven distribution of energy in the global system.

2.3. Reaction: 2nd Law of Thermodynamics -- Nature works to undo uneven energy distributions (and therefore establish maximum disorder). Results in global-scale energy redistribution via the Earth's fluid media (oceans and atmosphere).

2.4. Global temperature distribution: Effects of different surfaces (land vs. sea) and latitude; isotherms. Different surfaces have different specific heat coefficients, causing them to heat and cool at different rates.

3.1. Three-cell related forcing results in hemispheric-scale pressure differences. Mass piling up above the tropical and polar regions of both hemispheres create semi-permanent high-pressure systems. Mass leaving the equatorial and subpolar regions create semi-permanent low-pressure systems (illustration here).

3.2. Cooler air = Denser air (see Ideal Gas Law). Denser air has less volume and therefore settles closer to the Earth's surface. This creates "low area" in the upper atmosphere that gravity fills with even more air from the sides. Thus horizontal temperature gradients result in mass concentrations over a cold location, resulting in horizontal pressure differences. Land cools about four times faster than the sea surface, so these "cold-core highs" form over high-latitude land masses.

3.3. Warmer air = Less dense air. Lighter air has greater volume and therefore expands upward away from the Earth's surface. The creates a "high area" in the upper atmosphere which pushes mass off to the sides. Thus horizontal temperature gradients result in mass shortages over a warm location, resulting in horizontal pressure differences. Land heats up about four times faster than the sea surface, so these "warm-core lows" form over low-latitude land masses.

3.4. Isobars; pressure gradient force (PGF).

4.1. Gravity (GF).

4.2. Coriolis, a.k.a. Horizontal Deflection Force (HDF).

4.3. Pressure Gradient Force (PGF).

4.4. Centrifugal Force (CF).

4.5. Friction (FF).

4.6. Electricity is also a force at play in meteorology, but tends to be (a) very weak on a global scale (the global electric circuit), and (b) highly localized when comparable in strength to the other forces (as in a thunderstorm).

5.1. Geostrophic -- Balance of PGF and HDF (illustration here).

5.2. Cyclostrophic -- Balance of PGF and CF.

5.3. Cyclonic and anticyclonic -- Balance of PGF, HDF and CF.

5.4. Physical -- Balance of PGF, HDF, CF, and FF.

5.5. Divergence/convergence in/out of pressure systems due to FF.

LAB:

1. Introduction to surface charts.

2. Analyze a surface chart for temperature and pressure. Compare regions of high wind speeds to areas of tight pressure or temperature gradient.

HOMEWORK:

1. Read Lutgens and Tarbuck chapters 6 (pp. 171 - 183) and 7.

2. Analyze another surface chart for the same parameters as you did in the lab. Download the pre-plotted chart from the SUNY Albany Weather Page. See "Surface and Upper-Air Data," then "Surface Map of the United States." This will be collected at the beginning of the next meeting.