Investigation 9A

DataStr= eme Atmosphere Current Weather Studies 9A:

WESTERLIES AND THE JET STREA= M

Do Now:

Print this file.
Print the Monday Current Weather Studies Image 1, Image 2 and Image 3 Files.
When available, answer the two Concept of the Day questions in the Tuesday, 3 November 2009 Daily Summary File.

To Complete Investigation:

Read Chapter 9 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].
Complete the introductory portion of Investigation 9A in the Weather Studies Investigations M= anual, which ends when you reach the statement, "As directed by your course instructor, complete this investigation by either: ---.&quo= t; [Do not complete the Applications portion of the Investigation.= ]
Go to the Monday - CWS= A (Current Weather Studies A) link on the course website to complete this investigation.

Over the end of last week and the past weekend, a strong storm system mo= ved northeastward from the north-central portion of the country accompanied by heavy rains for much of the eastern half of the U.S. Many "trick or treaters" in the Northeast probably got wet on Saturday night.

1= . Image 1 is the surface weather map for 12Z 31 OCT 2009, Saturday morning. At = that time, the storm's intense low-pressure center was just north of the map area over Hudson Bay in Canada with a long trailing cold front over the eastern U.S. to southern Mexico. Also, a warm front extended southeastward over t= he northern tip of Maine. Additionally, a secondary cold front trailed the first, from the western Gr= eat Lakes to Arkansas= . The second front marked the leading edge of even cooler and drier air. A br= oad band of precipitation stretched from the warm sector of the storm in Quebec and between the cold fronts to the Gulf of M= exico (the limit of U.S. radar coverage).

Although station models are not plotted in Ca= nada, the winds shown over the Great Lakes region and the northeastern U.S. indic= ated that the flow about the Hudson Bay Low center was [(clockwise and outward)(counterclockwise and inward)].

2= . From the number of isobars plotted over the Great Lakes and eastern Canada,= one can conclude that there was a relatively [(strong)(weak)] pressure gradient associate= d with this storm system near its center. Confirmation of this can be seen with the innermost isobar over Hudson Bay being 972 mb (= inside the 976 mb shown) and the pressure at Buffalo, NY being 1000.7 mb. Buffalo's winds were averaging 30 knots= !

3= . Image 2 is the 500-mb constant-pressure map for Saturday morning 12Z 31 OCT 2= 009, the same time as the Image 1 surface map. The 500-mb pressure level is foun= d in the [(lower)(middle)(upper)] troposphere.

4= .      The major upper-air flow pattern feature at 12Z 31 OCT 2009 as shown on the 500= -mb map was one of a [(trough)(<= u>ridge)] in the central U.S.<= /st1:place> There also existed a weak ridge in the western U.S.

5= .      Recall that the heights at which the radiosondes detec= ted 500-mb of pressure are reported in the upper right position of the upper-air station models on the map. Also, the heights are plotted in tens of meters, so that a "0" needs to be added to the digits for = the actual height. The height of the 500-mb pressure level plotted on the International Falls, MN station model on the Can= adian border was [(5290)(5470)(5680)] m.

6= .      Taking the southern-most extension of each contour on the 500-mb map from Lake Superior to the Gulf of Mexico, draw a d= ashed line through those southern extensions. This dashed line marks the trough line where winds generally change from being northeasterly to the west = of that line to being southwesterly east of the line. Also, sketch the general position of the eastern-most cold front of the surface map onto this 500-mb map.

The cold front extending from the Hudson Bay = Low was generally located to the [(east)(<= /span>west)] of the trough line of the middle-level circulation. While not readily appar= ent on these maps, the surface Low center over Hudson Ba= y is to the east of the 5220-m contour plotted along the northern edge of the Image 2 map.

7= .      The highest wind speed plotted on the 500-mb map is at Detroit, MI where there = are two pennants, three long feathers and one short feather for a total speed o= f [(75)(135)(195)] kts from the south-southwest, much higher than surface wind speeds.

8= .      Image 3 is the 300-mb constant-pressure map for 12Z 31 OCT 2009, the same tim= e as the surface and 500-mb maps. The general 300-mb contour pattern at 12Z on 31 OCT across the central U.S. evidenced a [(trough)(rid= ge)]. The weak western ridge that was evidenced on the 500-mb map was also presen= t.

9= .      The heights of the 300-mb pressure level were within several hundred meters of = [(5500)(9200)(12,500)] meter= s at that location in the upper troposphere.

1= 0. Compa= ring the heights of the 300-mb pressure surface from south to north on the map, = as latitude increases (one moves poleward) the hei= ght of the 300-mb surface generally [(increases)(remains the same)(decreases)]. There is a corresponding change in temperature, confirming that pressure decreases more rapidly in colder columns of air than warmer ones (again recall Investigation 5B).

1= 1. The d= ashed lines on the 300-mb map are lines of equal wind speed, isotachs, drawn every 20 knots for wind speeds of 30 knots and higher. The highest wi= nd speed at 300 mb plotted on the Image 3 map is at Gaylord in northern Michigan<= /st1:place>. The three pennants, four long feathers and a short feather indicates a spee= d of about [(75)(135)(= 195)] knots.

1= 2. Using= the conventional wind speed threshold of 70 knots for defining the existence of= a jet stream, there [(was)(was not)] evide= nce of a jet stream indicated on the 12Z 31 OCT 2009 300-mb constant-pressure m= ap stretching across the U.S.

1= 3. Compa= ring the wind speeds plotted on the Image 3, 300-mb constant-pressure map with t= hose of the corresponding areas on the Image 2, 500-mb map, shows that wind spee= ds typically [(decrease)(remain the same)(increase)] in the troposphere as altitude increases (pressure decreases).

1= 4. There= are two 170-kt isotachs on the 300-mb constant-pres= sure map that encompass regions of the highest wind speeds. One small oval area = is over the Illinois-Indiana border while the second is over northern Michigan and Lake Huron. Shade those areas within the 170-kt isotachs. T= hese high speed regions are located generally to the [(west)(east)] of the 300-mb trough axis. = These high speed regions within the overall jet stream flow are called jet str= eaks.

1= 5. From = the 500-mb and 300-mb winds shown on each respective map, where wind speeds are highest, the contour spacings are generally relatively [(far apart)(c= lose together)]. This relationship of wind speed to contour spacing = is consistent with that on surface weather maps between wind speed and isobar spacing.

1= 6. Also, comparison of the 500-mb and 300-mb winds on each respective map, shows that the wind directions are generally [("parallel" to the contour lines)(directed across con= tours at large angles)]. This directional relationship holds particul= arly for higher wind speeds.

Upper air flow changes from zonal to meridional, and back again, with passing storm systems. And jet streams accompany the storms as they develop and dissipate. They also wander from south to north and back again. You can watch these changes by following the upper level maps on the course website.

Place the answers to Current Weather Studies investigations 9A and 9B on= the CWS Answer Form (provided from the DataStreme Atmosphere website on Wednesdays).

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