NATS 101 Lecture 15 Surface and Upper-Air Maps

Supplemental References for TodayÕs Lecture

	Gedzelman, S. D., 1980: The Science and Wonders of the Atmosphere. 535 pp. John-Wiley & Sons. (ISBN 0-471-02972-6)

Summary

	Because horizontal pressure differences are the force that drives the wind
	Station pressures are adjusted to one standard levelÉMean Sea LevelÉto mitigate the impact of different elevations on pressure

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Surface Maps

	Pressure reduced to Mean Sea Level is plotted and analyzed for surface maps.
	Estimated from station pressures
	Actual surface observations for other weather elements (e.g. temperatures, dew points, winds, etc.) are plotted on surface maps.
		NCEP/HPC Daily Weather Map

Isobaric Maps

	Weather maps at upper levels are analyzed on isobaric (constant pressure) surfaces.
	(Isobaric surfaces are used for mathematical reasons that are too complex to explain in this course!)
	Isobaric maps provide the same information as constant height maps, such as:
		Low heights on isobaric surfaces correspond to low pressures on constant height surfaces!
		Cold temps on isobaric surfaces correspond to cold temperatures on constant height surfaces!

Isobaric Maps

Contour Maps

	Display undulations of 3D surface on 2D map
	A familiar example is a USGS Topographic Map
	ItÕs a useful way to display atmospheric quantities such as temperatures, dew points, pressures, wind speeds, etc.

Rules of Contouring (Gedzelman, p15-16)

	ÒEvery point on a given contour line has the same value of height above sea level.Ó
	ÒEvery contour line separates regions with greater values than on the line itself from regions with smaller values than on the line itself.Ó
	ÒThe closer the contour lines, the steeper the slope or larger the gradient.Ó
	ÒThe shape of the contours indicates the shape of the map features.Ó

Contour Maps

	ÒTo successfully isopleth the 50-degree isotherm, imagine that you're a competitor in a roller-blading contest and that you're wearing number "50". You can win the contest only if you roller-blade through gates marked by a flag numbered slightly less than than 50 and a flag numbered slightly greater than 50.Ó

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Key Concepts for Today

	Station Pressure and Surface Analyses
	Reduced to Mean Sea Level Pressure (SLP) PGF Corresponds to Pressure Differences
	Upper-Air Maps
	On Isobaric (Constant Pressure) Surfaces   PGF Corresponds to Height Sloping Downhill
	Contour Analysis
	Surface Maps-Analyze Isobars of SLP                     Upper Air Maps-Analyze Height Contours

Key Concepts for Today

	Wind Direction and PGF
	Winds more than 1 to 2 km above the ground are perpendicular to PGF!
	Analogous a marble rolling not downhill, but at a constant elevation with lower altitudes to the left of the marbleÕs direction

Assignment

	Topic – NewtonÕs Laws
	Reading - Ahrens pg 150-157
	Problems - 6.12, 6.13, 6.17, 6.19, 6.22 (6.13, 6.14, 6.18, 6.20, 6.23)