MIME-Version: 1.0 Content-Location: file:///C:/D9279B02/Investigation6B.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" Investigation 6B

DataStr= eme Atmosphere Current Weather Studies 6B:

RISING AND SINKING AIR

To Complete Investigation:

  1. Read Chapter 6 in the DataStreme Atmosphere textbook and respond to the Chapter Progress Questions in the DataStreme Atmosphere Study Guide Investigations binder. [Do not complete the Questions for Review and Critical Thinking Questions appearing in the = Weather Studies Investigations Manual].
  2. Complete the introductory portion of Investigation 6B in the Weather Studies Investigations Manual, which ends when you reach the statement, "As direc= ted by your course instructor, complete this investigation by either: ---<= /b>." [Do not complete the Applications portion of the Investigation.= ]
  3. Go to the Wednesday - = CWS B (Current Weather Studies B) link on the course website to comple= te this investigation.

In the Monday, Current Weather Studies (CWS) 6A, we examined an early se= ason winter storm that affected the northern plains bringing heavy snowfall to t= he region. Denver, Colorado was a recipient of some of th= at snow. Here we will further consider where vertical air motions associated w= ith the passage of the storm system were depicted on a St&= uuml;ve diagram.

1= .      Let's go back and reconsider the Image 3 sounding at Denver at 12Z on 11 OCT 2009. From the sounding data (not shown) the surface temperature was –3.3 °C and= the dewpoint –6.8 °C at that time. This difference between the temperature and dewpoint= indicates that the air at the surface in Denver [(was)(was not)]<= /b> saturated.

2= .      As we determined in CWS 6A, the air flow westward toward the mountains was cau= sing the air to undergo orographically forced [(<= i>rising)(sinking)] vertical motion.

3= .      Therefore, the air moving vertically above the surface at 12Z on 11 OCT in Denver would be <= b>[(warming)(cooling)] adiabatically. This is s= hown on the Image 3 Stüve diagram.

4= .      The rate of temperature decrease plotted on the Stüve= diagram from the surface to about 780 mb is par= allel to the neighboring [(dry)(saturated)] adiab= atic lapse rate lines shown in green slanting from lo= wer right to upper left.

5= .      The Stüve diagram shows that the temperature b= ecame equal to the dewpoint at about [(850)(820)(780)] mb. At this level the air would become saturated and a cloud would begin to form.

6= .      The sounding text data gave the surface elevation as 1625 m (837 mb) and the 784 mb level = at 2134 m where the temperature was –8.3 °C, essentially the same as the = dewpoint. Consequently, there was a 5.0 C° temper= ature change over a 509-m altitude change. The temperature change over this altit= ude interval was therefore equivalent to 9.8 C°/1000 m. The cooling rate in= the near-surface air over Denver [(was)(was not)]<= /b> equal to the theoretical dry adiabatic rate.

7= .      From about 780 mb on the Denver Stüve diagram to about 740 mb, the temperature and dewpoint curves are equal meaning the air [(= was)(was not)] saturated.

8= .      The sounding text data further gave the 742 mb level as 2556 m where the temperature was –11.1 °C. The temperature change over this altitude interval (2134 to 2556 m)= was therefore 6.6 C°/1000 m. The cooling rate in this saturated air (cloud) over Denver [(was)(was not)] within a degree of the q= uoted saturated (or moist) adiabatic rate from the text of 6 C°/1000 m.

The vertical motions forced by the rising ter= rain in the Denver area showed that atmospheric motions do follow the predicted behavior. Reca= ll that the previous sounding (Image 2 of CWS 6A) indicated that those conditi= ons had persisted over the twelve-hour period.

9= .      Image 1 of this Wednesday Current Weather Study 6B is the surface weather map= for 00Z 14 OCT 2009, Tuesday evening. At that time a newsworthy storm system was battering the West Coast. Heavy rains were causing flooding and mudslides in areas affected by previous fires that removed protective vegetation. The copious moisture had been supplied by the remnants of Typhoon Melor (typhoon is the western Pacific name for hurric= anes). Following a westward path over the tropics, Melor then curved northwestward to graze Japan before weakening and merging into = a midlatitude storm system that crossed back eastward o= ver the Pacific Ocean. For details, see the Wednesday, 14 October 2009 Daily Weather Summary.

The surface temperature at San Francisco, in central coastal California, was 65 °F and the dewpoint was 60 °F. Therefore, the surface air at= San Francisco = [(was)(was not)] saturated.

1= 0.  Based= on the station model sky cover and the radar echo shadings of precipitation sh= own around the San Francisco<= /st1:PlaceName> Bay area, clouds [(were)(were not)] present above the surfa= ce.

1= 1.  There= fore, we can be confident that saturated air [(was)(was not)] present above the surface over the Bay area.

1= 2.  It ca= n be further assumed that the air over the Bay area was undergoing [(ri= sing)(sinking)] vertical motions above t= he surface. These motions were involved with the onshore flow toward rising terrain from the counter-clockwise and inward circulation seen behind the c= old front. This is consistent with the wind direction at = San Francisco.

1= 3.  Image 2 is the Stüve diagram from the Oakland (OAK) rawinsonde observation at 0000Z 14 OCT 20= 09, the same time as the Image 1 surface map. Oakland is the upper-air station across the bay from San Francisco. The temperature and dewpoint profiles from just above the surface in Oakland to about = 600 mb show that the air [(was)(was not)] saturated.

1= 4.  From = the Oakland text data= (not shown), the temperatures and dewpoints were equ= al from 996 mb to 609 mb. This equality means it [(was)(= was not)] likely that cloud was present in that layer.

1= 5.  From = 996 mb to 609 mb, the tempera= ture profile closely aligned with the [(straight, solid, green dry)(curved, dashed, blue saturated)] adiabatic lapse rate lines.

1= 6.  Over = Oakland, 996 mb occurred at 12 m and 609 mb was at 4063 m. Therefore, the cloud layer over Oakland was about [(1000)(2000)(4000)] m thick= . This is equivalent to almost 3 miles, a prodigious supplier of precipitation for this storm system. Similar conditions existed all along the coast.

As another example of temperature changes associated with a storm system, you might review the Stüve (Figure 4) that accompanies the Applications portion of Investigation 6B of the Weather Studies Investigations Manual.

Stüve diagrams of actual observations c= onfirm that vertical atmospheric motions do follow the theories! Call up these Stüves as dramatic weather changes affect your a= rea. Weather systems (Highs, Lows, fronts) force air to move vertically causing accompanying temperature changes. Flow forced over rising and sinking elevations, particularly in the western U.S. also drives atmospheric = temperature patterns.

Record your responses to items in CWS Activities 6A and 6B on the CWS Answer Form for transmission to your course mentor.

Instructions for Communications with Mentor:

After completing this week's applications, transmit the following work to y= our LIT mentor by Monday, 19 October 2009, or as coordinated with your mentor: =

  1. Investigations 6A and 6B = Investigation Answer Form, from the Study Guide, Week 6, or the DataStreme Atmosphere website.
  2. Investigation 6B page 6B-= 3.
  3. Current Weather Studies activities 6A and 6B CWS Answer Form.

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