Transcript Lecture 4a
Lecture 3 Vertical Structure of the Atmosphere Average Vertical Temperature profile Atmospheric Layers Troposphere On average, temperature decreases with height Stratosphere On average, temperature increases with height Mesosphere Thermosphere Lapse Rate Lapse rate is rate that temperature decreases with height T z Soundings Actual vertical temperature profiles are called soundings A sounding is obtained using an instrument package called a radiosonde Radiosondes are carried aloft using balloons filled with hydrogen or helium http://www.srh.noaa.go v/mob/balloon.shtml Radiosonde Application: Reduction to Sea Level (See Ahrens, Ch. 6) proportional to weight of this column of air Surface pressure here Surface pressure also called station pressure (if there is a weather station there!) Math psfc g dz z sfc Obtained by integrating the hydrostatic equation from the surface to top of atmosphere. Deficiencies of Surface Pressure Spatial variations in surface pressure mainly due to topography, not meteorology Height contours on topographic map Units: m It’s a mountain! 1050 1000 950 900 Put a bunch of barometers on the mountain. Surface pressure (approximately) Units: hPa 885 890 895 900 Isobar pattern looks just like height-contour pattern! “Reduction to Sea Level” is proportional to weight of this column of air Surface pressure here For sea level pressure Let T = sfc. temp. (12-hour avg.) add weight of isothermal column of air temp = T. Sea Level Pressure as Vertical Coordinate Pressure is a 1-1 function of height i.e., a given pressure occurs at a unique height Thus, the pressure can be used to specify the vertical position of a point At what height is the pressure equal to p? Given p Pressure Surfaces Let the pressure, p1, be given. At a given instant, consider all points (x, y, z) where p = p1 This set of points defines a surface z p = p1 z(x2) z(x1) x1 x2 x Height Contours Heights indicated in dekameters (dam) 1dam = 10m Two Pressure Surfaces z p = p2 z2 z2 – z1 z1 p = p1 Thickness z2 – z1 is called the thickness of the layer Hypsometric equation thickness proportional to mean temperature of layer Thickness Gradients z p = p2 Large thickness Small thickness warm Cold p = p1 Exercise Suppose that the mean temperature between 1000 hPa and 500 hPa is -10C. Calculate the thickness (in dam) R z 2 z1 ln 2 T g 287J kg-1 K 1 0.693 263.15K 2 9.81m s m 2 s 2 K 1 20.3 263.15K 2 ms 20.3m K 1 263.15K 5340m 534dam Repeat, for T = -20C z2 z1 20.3m K 1 253.15K 5140m 514dam Thickness Maps