Bulletin Board

Last Updated on DEC 12, 1999

Welcome to the bulletin board for AS3 discussion session 1G,1I and 1K. I am your TA and I will post any announcement about my session here. I will also post some questions asked by some students and try to anwser them here, please check this page if you have any questions. You can also email your new questions or feedbacks to the posted questions to me from this page.

Announcements

Exam #3 will be WEDNESDAY, DECEMBER 15 from 9 to 11 am in the ACKERMAN GRAND BALLROOM. Please bring a #2 pencil and your photo ID.

[1] Someone left her glasses at my office last week. PLease contact me so I can give it back to you.

[2] I will have a combined review session for discussion session F10 and F1 at 10 Am , this Friday. There will be no discussion session at 1Pm, this Friday

[3] I will have extra office hours from 2-5Pm, Monday and tuesday, just before your exam. If you have any questions, just come by.

GOOD LUCK !

Questions about HW #3

[1] Question 13 : The correct anwser should be (a) since it is the time when the temperature difference between land and sea is the largest.

How to prepare for your second midterm

This week is your second exam week. We will do a review on your exam. Since my session is relatively near exam, I post the following exam topics which Jeff told us. You guys should go through these topics and make sure you understand them. If not, be prepared to ask questions about these topics in our review session.

According to Jeff, the topics for second exam should include:

humidity (all), condensation (dew, fog), cloud formation (mechanisms and stability), cloud identification, precipitation, and whatever stuff on atmospheric pressure I get to finish by this Friday's lecture (probably just heights vs. temperature, hydrostatic balance, and barometers)".

You should concentrate on:

* e vs. RH vs. DP (many students seem to confuse the meaning of physical units, so we got stuff like "vapor pressure = temperature" on the previous exam)

* fog vs. cloud formation

* environmental vs. parcel temperature during parcel movements (e.g., the first problem on the homework)

* stability conditions and the effects on cloud formation (which will then be related to cloud identification)

* precipitation formation vs. temperature (i.e., collision/coalescence vs. ice crystal process + accretion), which is related to the fact that most precip over L.A. begins as snow.

I think the best way to review is read through your book, go through Hw#2 and lab #2, look at the sample questions on the web. If you have any questions, just come to my office hours.

Good Luck

NOTICE : There is a small clarification of HW#2, question 1, section iii. Instead of saying "all the precipitation, if any, has fallen out", we should say," all the liquid water, if any, has fallen out"

If you have any questions about homework, you can come to my office hours OR email me. I am always willing to help, only if you guys ask.

Questions,Anwsers and Hints About Your Homework

HOMEWORK #2

Q[1] For Hw #2,please explain how to do problem #1 parts ii) & iii), I don't understand.

Problem #1, part ii):

When air parcel rising, if it is unsaturated, its temperature will change according to dry-adiabatic lapse rate, which is 10 C/km. In this question, air parcel temperature at the surface is 10 c, which is the same as the environment. When this air parcel starts to rise, its temperature will decrease according to dry-adiabatic lapse rate, that is, its temperature will decrease 10 c every km. We assume the air parcel dew point temperature stays the same, and we know that when air parcel temperature equals its dew point temperature, air parcel will become saturated, and a cloud will start to form. After you understanding all this, you only need to find the height at which the air parcel temperature=dew point temperature=-10c. The anwser is obvious 2.0 km.

Problem #1, part iii)

The temperature change of air parcel go through a process like this:

First: since this air parcel is sub-saturated at surface, its temperature will decrease with height every 10 c per km(dry-adiabatic) until it becomes saturated; find the height where the air parcel becomes saturated and find the temperature of the air parcel.( actually the height is already found in part ii)

Second: start from the height where the air parcel is saturated, when the air parcel keep going up, its temperature will decrease with height according moist-adibatic lapse rate, that is, every 6 c per km. The air parcel keep changeing its temperature this way until it reach the height of mountain. Find the temperature of air parcel at the height of the mountain.

Third:our big assumption come into play at this stage: we assume all the liquid water, if any, will fallen out at the mountain top. That means, our air parcel only has water vapor left in it, all liquid water is gone. Then, when this air parcel starts to descent on the leeward side of the mountain, it will undergoing compressional warming according to dry-adibatic lapse rate. That means, the air parcel temperature will increase 10 c per km when it descending on the leeward side of the mountain. Knowing all of this, you sould be able to figure out the anwser to part(iii). it is 14 C.

If you have trouble understanding the above argument, please see me at our session or at my office hours.

Question #7:

assume the pressure at the surface is 1000mb. Since the pressure is caused by the weight of air above you, at surface, the pressure is 1000mb, when you move up to the 850 mb level, the air above you give you a pressure of 850mb, therefore, there should be 850mb/1000mb, which is 0.85=85% of air still above you, 15% is below you. See figure 1.6 at page 8, you should be able to find anwsers there.

Question #9:

Usually in the troposphere, the temperature decrease with height. Why the warm air just doesn't go up ? That's because if the air does go up, its temperature will decrease ( Expantional cooling), for the lapse rate of normal atmosphere, the expantional cooling will make the air parcel to be colder than its environment, so it will sink, that's why the troposphere does not turn over.

Question #3, in the book it says that all 5 choices are important, but in lecture he only mentioned 3 of the 5. What's up with that?

Just stick with the book, all of them should be important.

HOMEWORK #1

Q[1] For Hw #1,question #5, how do figure out i,ii,iii? (Stuff about Planet X) How do you find the position of the Arctic Circle, Tropic of Cancer, and seasonal shifts of Planet X?

(I) the arctic circle is the place where you start to have 24 hrs daytime during Summer Solstice and 24 Hrs nighttime during Winter Solstice. The position( Or Latitude) of artctic circle is decided by the tilting angle of the earth.

The latitude of arctic circle = (90 - tilting) North

(II) On Summer soltice for Northern Hemisphere, the sun is directly over the tropic of cancer. The latitude of Tropic of Cancer is equal to the tilting Angle for the Norther Hemisphere.

(III) The extreme of season is decided by the tilting angle. The larger the tilting, the extreme the season.

if you don't understand why (i),(ii) and (iii) make sense, please see me at your convinent time.

Q[2] For Hw #1, question #10, the earth emits radiation 24 hrs. per day, right?

Right. Anything above absolute zero degree will emit energy 24 hr a day and seven days a week( Hard working, right ?)

Q[3] For Hw #1, question #10, a west wind is not blowing to the west because it's blowing from west to east, right?

Right. In meteorology, when we say a west wind, we mean the wind is blowing from west to east. That is, we define wind by the direction it comes from, not by the direction it goes to.

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