Lab Exploration #7: Winds and Pressure Patterns

Transcription

1 METR 104: Our Dynamic Weather (w/lab) Lab Explratin #7: Winds and Pressure Patterns Dr. Dave Dempsey Dept. f Gesciences SFSU, Spring 2013 (5 pints) (Lab Sectin 1: Wed., April 24; Lab Sectin 2: Fri, April 26) Objectives. By the end f this lab explratin, yu shuld be able t: Develp generalized, qualitative relatinships between winds (bth speed and directin) and atmspheric pressure patterns, based n a set f bservatins: near the earth s surface higher in the trpsphere ("alft") Estimate the directin and relative strength f the hrizntal pressuregradient frce (PGF) at specific lcatins n a cntur map f pressure Recgnize limitatins f using PGF patterns t deduce wind patterns Understand the lgical terms "prve", "cnfirm" r "supprt", "discnfirm" r "nt supprt", and "disprve", and apply them t evaluate statements abut relatins between winds and pressure patterns based n a set f bservatins. Materials. Maps f pressure and winds: Figure 1: Sea-level pressure isbars and surface winds fr 00Z Octber 19, 2012 Figure 2: Sea-level pressure isbars and surface winds fr 12Z Octber 21, 2012 Figure 3: Pressure isbars and winds alft (in mid-trpsphere arund ~18,000 19,000 ft., where the pressure is arund 500 mb) fr 12Z Nvember 10,

2 Backgrund. Cncepts t be cvered in lab befrehand (see handut, "Sme Imprtant Pints abut Winds and Pressure Patterns"): Als: Pressure and frce Cntur lines f cnstant pressure (isbars) n a weather map sea level pressure pressure alft (e.g., in mid-trpsphere) Features f pressure patterns high and lw pressure areas hrizntal pressure gradient the relatin between pressure gradient and the spacing and rientatin f isbars the relatin between pressure gradient and net frce n air (pressure gradient frce) due t pressure differences between places The meaning f the fur terms belw, frm the lgic f evidence (see the accmpanying handut, Prf, Cnfirmatin, Discnfirmatin, and Disprf: Reasning frm Evidence in Science ): prve cnfirm (r supprt) disprve discnfirm (r nt supprt) General Instructins: Fr the questins belw, refer t the accmpanying Figures 1, 2, and 3. Respnd in writing t the questins and turn in yur respnses at the end f the lab sessin. The Pattern at the Earth s Surface Figure 1 shws cntur lines f sea level pressure (isbars), tgether with bserved surface winds represented using the cmmn stem-and-barb cnventin. (See "The Statin Mdel" if yu need t review this. Recall that the statin is lcated at the head f the stem, at the ppsite end f the stem frm the barb(s).) The bservatins were made at 00Z Octber 19, Figure 2 shws the same thing, at 12Z Octber 21, We can figure ut the directin and relative strength f the pressuregradient frce at any particular place based n the rientatin and relative spacing f the isbars there. 2

3 Questin 1: Fr each f the statements (a) and (b) listed belw, decide whether the infrmatin n Figures 1 and 2: disprves the statement discnfirms the statement (that is, desn't supprt it, with perhaps a few exceptins) cnfirms the statement (that is, supprts it, with perhaps a few exceptins) prves the statement, r lacks any bvius bearing n the statement Fr each statement, explain yur cnclusin. Statement (a): The pressure-gradient frce alne determines the wind directin. (Hint: Pick several different places in the pressure pattern ver land where there are wind bservatins. Determine the directin f the pressure gradient frce at thse places. Then, assuming that statement (a) is true, determine what directin the wind shuld be blwing, and cmpare that directin with the bserved wind directin.) Statement (b): Winds are usually faster where the pressure gradient (and hence the pressure-gradient frce) is larger. (Fr this questin, cmpare land areas with ther land areas but nt with cean areas. Als, things might get mre cmplicated in muntainus areas, s try t avid thse.) 3

4 Questin 2: If it is pssible based n these bservatins, what generalizatin might yu make abut the wind directin relative t the rientatin f the isbars, especially ver land areas? (Fr example, des the wind generally blw parallel t the isbars? Or perpendicular t isbars tward lwer, r tward higher, pressure? Or acrss isbars tward their lwer, r higher, pressure side, but nt perpendicular t them instead, angled clckwise, r cunterclckwise, frm the perpendicular directin?) The Pattern Alft Figure 3 shws the pattern f pressure in mid-trpsphere, at an altitude f 18,000-19,000 feet (abut 5-6 kilmeters) abve sea level. At this altitude the pressure is arund 500 mb, rughly half f typical sea level pressures. (As a side nte, rughly half f the mlecules f air in the atmsphere and therefre half f the ttal mass f air in the atmsphere lies belw this level and the ther half lies abve it.) The cntur lines n Figure 3 aren't actually isbars, but we can treat them as if they were. If they were actually isbars, then the pressures wuld be arund 500 mb and the cntur interval wuld be abut 10 mb. Figure 3 als shws winds bserved at this level by radisnde ballns launched frm the earth s surface. The winds are represented using the standard stem-and-barb cnventin. The pressure pattern alft (that is, significantly far abve the surface f the earth, as in Figure 3) is ften quite different frm what it is at the surface. 4

5 Questin 3: Hw might yu generalize the relatin between wind directin and the rientatin f isbars at this level alft (if there seems t be any relatin)? Des this differ frm yur answer t Questin (2) abve? Questin 4: At the level alft shwn in Figure 3, des there seem t be any cnnectin between wind speed and the magnitude f the pressure gradient? If s, what is it? Questin 5: At either the surface r alft, des the pattern f pressure-gradient frce alne (which we can determine frm the pressure pattern) seem adequate t explain the bserved pattern f winds (bth speeds and directins)? Explain why yu think s. 5