Wednesday Oct. 24, 2007

1S1P Assignment #2 reports were collected today.

Quiz #3 is one week from today (Wed., Oct. 31).  The complete Quiz #3 Study Guide is now online.

The Experiment #3 reports are due next Monday.  Please try to return your materials by Friday, the experiment materials are needed for another class next week.  Once you return the materials you can pick up a copy of the supplementary information sheet.

Computer generated grade summaries were distribted in class today.  Please verify that the information recorded on your grade summary is correct.

We didn't finish the discussion of satellite photographs in class on Monday.  Quite a bit of additional information was added to the Mon. Oct. 22 notes that was not covered in class.

Today we will first look at 35 mm slides of most of the 10 cloud types.  Good photographs of the ten cloud types can also be found in Chapter 4 of the text and in a Cloud Chart at the end of the textbook.  You'll find the written descriptions of the cloud types in the images below on pps 97-98 in the photocopied notes.

High altitude clouds are thin because the air at high altitudes is very cold and cold air can't contain much moisture (the saturation mixing ratio for cold air is very small).  These clouds are also often blown around by fast high altitude winds.  Filamentary means "stringy" or streaky.  If you imagine trying to paint a Ci cloud you would dip a stiff brush in white paint brush it quickly and lightly across a blue colored canvas. 


A cirrostratus cloud is a thin uniform white layer cloud (not purple as shown in the figure) covering part or all of the sky.  Here you might first dilute your white paint with water and then brush back and forth across the canvas.  The thin white paint might not be thick enough to hide the blue canvas but the white coating on the canvas would be uniform not streaky like with a cirrus cloud.

To paint a Cc cloud you would dip a sponge in white paint and press it gently against the canvas.  You would leave a patchy, splotchy appearing cloud (sometimes you might see small ripples).  It is the patchy (or wavy) appearance that makes it a cumuliform cloud.

Note since it is hard to accurately judge altitude, you must rely on cloud element size to determine whether a cloud belongs in the high or middle altitude category.  The cloud elements in Ac clouds appear larger than in Cc because the cloud is closer to the ground.

Lenticular clouds (see Fig. 4.33 on p. 105 in the text) are a special type of altocumulus cloud.

When (if) an altostratus cloud begins to produce precipitation, its name is changed to nimbostratus.

This cloud name is a little unusual because the two key words for cloud appearance have been combined.  Because they are closer to the ground, the separate patches of Sc are about fist size.  The patches of Ac, remember, were about thumb nail size.

There weren't any examples of stratus clouds in the slide collection.

Cumulus clouds come with different degrees of vertical development.  The fair weather cumulus clouds don't grow much vertically at all.  A cumulus congestus cloud is an intermediate stage between fair weather cumulus and a thunderstorm.

There are lots of distinctive features on cumulonimbus clouds including the flat anvil top and the lumpy mammatus clouds sometimes found on the underside of the anvil.  Cold dense downdraft winds hit the ground below a thunderstorm and spread out horizontally underneath the cloud.  The leading edge of these winds produces a gust front.  Winds at the ground below a thunderstorm can exceed 100 MPH, stronger than many tornadoes.  The top of a thunderstorm is cold enough that it will be composed of just ice crystals.  The bottom is composed of water droplets.  In the middle of the cloud both water droplets and ice crystals exist together at temperatures below freezing (the water droplets have a hard time freezing).  Water and ice can also be found together in nimbostratus clouds.  We will see that this mixed phase region of the cloud is important for precipitation formation.  It is also where the electricity that produces lightning is generated.

Here's one final feature to look for at the bottom of a thunderstorm. 

Cold air spilling out of the base of a thunderstorm is just beginning to move outward from the bottom center of the storm in the picture at left.  In the picture at right the cold air has moved further outward and has begun to get in the way of the updraft.  The updraft is forced to rise earlier and a little ways away from the center of the thunderstorm.  Note how this rising air has formed an extra lip of cloud.  This is called a shelf cloud.  You'll find a good photograph of a shelf cloud in Fig. 10.7 in the text.