Transcript Document
NATS 101 Lecture 15 Surface and Upper-Air Maps Supplemental References for Today’s 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 level…Mean Sea Level…to mitigate the impact of different elevations on pressure PGF Ahrens, Fig. 6.7 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 (Constant height) 496 mb 504 mb Some generalities: 1) The 2) 3) Warm/Cold High/Low PGF on heights temps an isobaric on onan ansurface isobar isobaric surface correspond corresponds to the downhill to Warm/Cold High/Low direction temps pressures on a constant on aheight constant surface height surface Ahrens, Fig. 2, p141 Contour Maps Display undulations of 3D surface on 2D map A familiar example is a USGS Topographic Map It’s a useful way to display atmospheric quantities such as temperatures, dew points, pressures, wind speeds, etc. Gedlezman, p15 Rules of Contouring (Gedzelman, p15-16) “Every point on a given contour line has the same value of height above sea level.” “Every contour line separates regions with greater values than on the line itself from regions with smaller values than on the line itself.” “The closer the contour lines, the steeper the slope or larger the gradient.” “The shape of the contours indicates the shape of the map features.” Contour Maps “To successfully isopleth the 50degree isotherm, imagine that you're a competitor in a rollerblading 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.” https://www.e-education.psu.edu/gened/meteo101/Examples/Section2p02.html Click “interactive exercise” From https://www.e-education.psu.edu/gened/meteo101/Examples/Section2p03.html https://www.e-education.psu.edu/gened/meteo101/Examples/Section2p04.html Click “interactive isotherm map” 570 dam contour 576 dam contour 570 and 576 dam contours All contours at 6 dam spacing All contours at 6 dam spacing -20 C and –15 C Temp contours -20 C, –15 C, -10 C Temp contours All contours at 5o C spacing Height contours Temp shading PGF Wind 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 marble’s direction Assignment Topic – Newton’s 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)