Lecturer: Prof. Elizabeth A. Ritchie, ATMOTAs: Ms. Simona Olson

NATS 101

Introduction to Weather and Climate

Section 5: T/R 2:00 – 3:15 pm ILC 120

Important Information• Office Hours:

Prof. Ritchie – T/W 11:00-11:50 am or by appointment, PAS 570 Ph: 626-7843(except Aug 25 - Sep 14)

Ms. Olson – T 3:30-5:00 pm & W 3:00-4:00 pm or by appointment, PAS 526 Ph: 621-6843

• Required Text: Understanding Weather and Climate, 4rd Ed. by E. Aguado and J. E. Burt

Attendance Policy

Attendance is mandatory, and I reserve the right to tally it throughout the term.

http://catalog.arizona.edu/2006-07/policies/classatten.htm

Attendance does go into your grade and can make the difference between a higher or lower letter grade if you are borderline.

Student Behavior

UA Code of Academic Integrity, Code of Conduct and Student Code of Conduct are enforced in this course.

Every student is responsible for learning these codes and abiding by them. http://w3.arizona.edu/~studpubs/policies/ppmainpg.html

Students can submit complaints online at http://web.arizona.edu/~dos/uapolicies/

Grading: Homeworks

• There will be eight homeworks throughout the semester, which are to be downloaded and printed off from the Course website by each student. Dates when they become available, and when they are due are listed on the website. Homeworks are due at the beginning of class on the dates shown.

• The lowest score among the eight homeworks will be dropped from the course grade.

*** THEREFORE, NO LATE HOMEWORKS

WILL BE ACCEPTED ***

Grading: Weather DiagramYou will each prepare a time series chart of sea-level pressure (SLP) and

temperature (T) observations recorded from the Tucson NWS office for the month beginning September 17.

In addition, you will take your own personal observations of the weather every day noting special conditions, e.g., windy, rain, hot, cold, etc, and add these to the time series.

You will prepare a half page text analysis of the observations discussing the relationship between the temperatures, sea-level pressures, and weather conditions of the day.

Details of how you will accomplish this are provided on the course website.

The neatly drawn, completed chart will be turned in with your second midterm exam for grading and credit. Note: you will need the weather diagram to answer questions on the midterm exam.

Grading: Midterm Exams

• There will be three midterm exams at regular intervals through the semester. These will occur on September 18, October 23, and November 20. These dates are listed in the course outline provided on the website.

• Students who arrive late on midterm days will be not allowed to take the exam after the first student turns in her/his exam.

NO EXCEPTIONS

• The lowest score among the three midterm exams will be excluded from the course grade.

*** THEREFORE, NO MAKE-UP EXAMS ***

Grading: Final Examination

Section 5 (2:00 pm T/R): ILC 120December 16, 2:00 pm - 4:00 pm

No Exceptions per UA Policy

• The final will be comprehensive, covering all material from the course.

• I suggest you double-check the date and time of this exam.

Grading Algorithm

• 25% Homework (lowest score dropped)• 15% Weather Diagram• 25% Midterm Exams (best 2 of 3 scores)• 25% Final Exam • 10% Class Participation

NO EXTRA CREDIT PROJECTS. NO EXCEPTIONS.

SO PLAN ACCORDINGLY!SO PLAN ACCORDINGLY!

Course Grading

• Course Grading ScaleA 90% or higher B 80.0-89.99% C 65.0-79.99% D 55.0-64.99% E < 55.0%

Lecture Notes:

for the next lecture will be made available in a printer-friendly pdf format the afternoon after the current lecture is over.

Print them off and bring them to class. The lectures are almost exclusively power-point-based and you will need the prints to make notes on

The Golden Rule

Instructor and students all show:

Mutual Respect!What exemplifies respectful behavior?

No talkingTurn off cell phones/pagers/ipods…

Arrive on timeRemain seated until dismissed

Literacy Requirements• Use scientific notation for writing numbers (especially rather

large or small ones). For example:

1,000,000.0 should be written as 1.0 x 106. 0.00006 should be written as 6.0 x 10-5.

• Specify units of physical quantities (e.g. meters for elevation, etc.). Marks will be deducted if units are missing.

• Always show all working. A correct number pulled out of a hat will NOT receive full credit!

• Basic algebra will be needed for some problems in this class. If you have trouble understanding how to do these problems, seek help early!

Class Format: Lecture Days

• 5-10 minutes - Announcements, Map Discussion and Forecast

• 2-3 minutes - Review/Summary/Clean-up From Prior Lecture (Optional)

• 60-65 minutes - New Material, Demos, Discussion

• 2-3 minutes - Wrap-up and Summary

AnnouncementsCourse Homepage…is functional!

http://www.atmo.arizona.edu/Click Course LinksClick NATS101 – Ritchie

All information pertaining to this course is contained on the webpage.

Review problem sets and solution sets will be provided through the webpage.

You should immediately get a U of A account if you do not already have one so that you can access this website and take advantage of the U of A computing facilities.

All email correspondence to myself or the TA should be via your .arizona.edu email otherwise it risks being automatically deleted as spam mail.

NATS 101

Weather Brief

Surface map showing weather observations (plotted using the station model notation),

fronts and satellite cloud photographs

Satellite cloud photographs with weather radar overlay

Surface weather map with isobars (pressure contours) and fronts

NATS 101

Lecture 1

Basic weather symbols and fronts

We describe weather in terms of:

temperature wind patternshumidity clouds visibilitypressure precipitation sunlight/UV

We “feel” weather as the heat we feel, the “weight” of the air we breathe.

If we observe these weather elements at an instance in time, then we obtain a measure of the weather

If we measure these weather elements over many years, then we obtain the “climate” of the region.

Therefore: - climate represents an average of daily weather over a

long period of time - Weather is the instantaneous condition of the

atmosphere.

“Climate is what we expect”

“Weather is what we get”

Atmospheric pressure impacts every aspect of weather although we do not easily recognize differences in pressure.

- Air moves from high pressure to low pressure → wind

- Air tends to rise in regions of low pressure and sink in regions of high pressure

Pressure Units: mb, hPa, inches Hg, mm Hg

Wind Units: m/s, mph, km/h, kts

Pressure and Wind

- tends to change gradually in horizontal or vertical directions

- also changes with time for the same weather system → diurnal cycle

- the only place there are rapid changes in temperature is in the vicinity of fronts

Units:- °C, °F, K

Temperature

- Two common ways to express the amount of water vapor in the air

- Relative Humidity:- is the amount of water vapor in the air relative to the maximum amount that could be present in the air. Units: %

- Dew Point Temperature:-

Td > 15°C is humid.

Td > 20°C is very uncomfortable.

Td < 5°C is dry.

Moisture: water vapor

L

H

Fronts:Cold air

Warm airWarm air

Cold air Cold air

Warm air

Cold front Warm front Stationary front

Pressure Systems:

low pressure

high pressure

Surface Map:

Upper-level Maps: 500 mb (hPa) (5 – 6 km or 16000 – 19000 ft)

Upper-level Maps: 300 mb (hPa) (9 – 10 km or 30,000 – 33,000 ft)

Weather Map SymbolsRef:- pg 525, Appendix C, Aguado and Burt

N

dd

ff

TT CM PPPCH

VV ww ppaTdTd CLNh WRt

h RR

N – total cloud coverdd – wind directionff – wind speed (kts)ww – present weather

PPP – barometric pressure (hPa) (add a 9 or 10 and place a decimal point to the left of last number)

TT– air temperature in °FTdTd - dewpoint temperature in °F

VV ppa34 CM 247

CH

30 CLNh WRt

h RR

Z (UTC) = MST + 7 i.e., 0000 UTC = 5:00 pm MDT 1200 UTC = 5:00 am MDT

Some basics of Frontal Systems (Chapter 9)

1. Fronts are boundaries that separate air masses with differing temperature and other characteristics.

2. Often represent boundaries between polar and tropical air - marked by sharp temperature changes over a relatively short distance.

3. Cold air is typically more dense than warm air → no mixing. Instead, the denser air forces the warmer air upward.

5. Fronts are marked by wind shifts.

4. This lifting of air upward can cause cloud formation and precipitation.

6. Fronts are marked by pressure and pressure changes.

Fronts:Cold air

Warm airWarm air

Cold air

Cold front Warm front Stationary front

Types of fronts:

Cold air

Warm air

Occluded front

Warm air

Cold air Coolerair

Cold FrontsCold fronts occur when a cold air mass “catches up” with a warm, generally unstable, air mass.

Cold air

Warmair

(relatively)

2 3°C-2°C-25°C

Day BirminghamSt. LouisMinneapolis1 5°C0°C-5°C

3 -5°C-12°C-28°C

Coldair

Warmair

Cold air advection

Cold Fronts

The cold air catches up with the warm air and it…

- The thunderstorms can produce very intense precipitation. - They only form right along the frontal boundary, - the fast movement of these fronts means that the precipitation is usually of short duration and clearing skies will soon follow.

The cold air mass moves in a different direction (W through N) than the warm air mass ( SW through S).

It is also moving faster.

1. pushes the warm, unstable air up because the cold air is denser 2. the cold air has a steep slope, because friction causes the lowest winds to slow down compared with winds higher up3. unstable rising air mass produces cumulo-type (thunderstorm) clouds

So what would our observer on the ground expect to see and feel with the passage of a “classic” cold front?

West-northwesterlyGusty, shiftingSouth-southwesterlyWinds

Steadily droppingSudden dropWarmTemperature

Rising steadilyMinimum, then sharp risefalling steadilyPressure

Often cumulusStrong cumulus clouds

Increasing cumulus-type cloudsClouds

Decreasing intensity, then

clearing

Heavy showers of rain or snow, sometimes

with hail, thunder, and lightening

Short period of showersPrecipitation

loweringSharp dropHigh: remains steadyDew Point

After PassingWhile PassingBefore PassingWeather element

Warm Fronts

Warm fronts occur when a warm, stable air mass “catches up” with a colder air mass.

Cold air

(relatively)

Warmair

Coldair

Warmair

Warm air advection

The warm air is moving faster than the cold air.The warm air is less dense than the cold air

The warm air “runs up” along the cold air boundary, which is not as steep as in the cold front case (over-running).

There are three consequences of this.

3. The precipitation out of this stratiform type cloud tends to be light and continuous, but owing to the large horizontal area of the cloud, and slow movement of these kinds of fronts, the rain can persist for days.

2. The warm air is stable and so it doesn’t form cumulo-type clouds as in the cold front case. Instead, as it is forced to rise, it condenses gradually forming a series of stratiform clouds, in a broad area.

1. The clouds and precipitation form well ahead of the surface front.

So what would our observer on the ground expect to see and feel with the passage of a “classic” warm front?

south-southwesterlyvariableSouth-southeasterlyWinds

Warmer, then steadySteady riseCool – cold slowly

warmingTemperature

Slight rise, followed by fallLeveling offUsually fallingPressure

Clearing with scattered ScStratus-type cloudsCi, Cs, As, Ns, St,

fogClouds

Usually none, sometimes light rain

or showersDrizzle or none

Light-to-moderate rain, snow, sleet, or

drizzlePrecipitation

Rise, then steadysteadySteady riseDew Point

After PassingWhile PassingBefore PassingWeather element

Stationary Fronts

Stationary fronts occur when the front stalls.

Coldair

Warmair

No air advection

The structure is the same as in other fronts, with the front sloping over the cold air mass.

There is no air movement across the frontal boundary, thus, there is no real weather.

Occluded FrontsAre associated with midlatitude cyclones that have both a cold front and a warm front associated with them.

Occlusion refers to “closure”. In this case, a faster moving cold front closes with the warm front.

As the cold front reaches the warm front, (and thus the cooler air in front of the warm front), the warm air mass is separated from the surface.

Because at the surface, the cold air mass is now “catching up” with a cooler air mass rather than a warm air mass the temperature change observed at the surface is not as dramatic.

An additional change is that now the warm, unstable air is no longer being strongly lifted by the cold front.

Thus, where the occlusion has occurred, only stable stratiform cloud develops accompanied by light but persistent rain similar to the warm front.

The cooler air that has replaced the warm air at the surface is not unstable.

Fronts:Cold air

Warm airWarm air

Cold air

Cold front Warm front Stationary front

Summary:- Types of fronts:

Cold air

Warm air

Occluded front

Warm air

Cold air Coolerair

L

Reading Assignment

• Aguado and Burt

Pages 21-26Pages 525-527 (Appendix C)