Download Sep 20, 2016

ERTH 365 Class Notes for September 20, 2016
Geneva Dunaway and Melissa Andrade
Assignments
- Storm and Hurricane Definitions
- Pielke and Pielke: Chapter 2 (Point of view: s​ocietal vulnerability to disasters associated with
hurrcianes​)
- Simmons and Sutter: Chapter 2; (Point of View: ​How do tornado frequencies suggest the
societal vulneratbility tornado disaster?​)
- Williams: Chapter 3 (all); Chapter 4 (Fronts), Chapter 5, 63-72. (The causes of wind, clouds,
and fronts)
- Zebrowski: Chapter 3, pp. 53-62; 77-83; 96-101; Chapter 5, pp. 143-145; 157-163 Chapter 8,
229-251 (The interrelationship of human settlement patterns and natural disaster, how winds
affect the surface of the sea, hurricane-related flood and wind disasters)
- Homework 1
- ​Exam on Thursday September 29th
Housekeeping
- briefly talked about the test next week
- picked up Surface Weather Map Data Plot handout
Current Weather Discussions
Looked at the Annual Mean Rainfall for California. San Francisco has 18-25 in annually, while
Marin, just one county over has 55in. This means it has 2x the amount of rainfall, not 2x the
amount of rainy days.
Cherrapunji, India
We focused on Cherrapunji, India because of its similarities to the Great Plains in the US.
Cherrapunji, India is famous for being “the wettest place on the planet”. It is located in the
mountains North of the Bay of Bengal. The winds come northward to Cherrapunji. In June the
average monthly rainfall was 100 inches with the yearly total of rainfall was 400 inches. The
max rainfall occurs during the summer time, similar to the areas in the US that get tornados.
Hurricane Paine
We viewed a tracking image and a satellite image of Hurricane Paine which is a Hurricane along
the coast of Baja California. We also viewed an infrared image of the hurricane as well as a
rainfall forecast image of the United States showing how many inches of rain certain areas would
get as of September 20, 2016. We specifically looked at the Baja California area which was
forecasted to get 1.50 inches of rain because of the hurricane.
Tracked Hurricane Pain near Baja, Ca. (​link​)
Hurricane Track: 6Z Sept 20, it became a Tropical Storm with a forecast to weaken.
Satellite Image: 12Z Sept 20, downgraded from a Hurricane to a Tropical Storm (​link​)
How can we infer where there were still thunderstorms on the satellite image?
The North part of the image has an area of condensed Cumulonimbus clouds.
Infrared Image: tops of the clouds ranged from -30⁰C to -50⁰C (​link​)
24hr Rainfall Forecast for Baja,Ca: 12Z Sept 20 - 12Z Sept 21 1-1.5in of rainfall (Baja Ca is a
desert, so annual rainfall is about 10in) (​link​)
National Hurricane Center (Miami, Fl)
Eastern North Pacific Region: X indicates areas of possible hurricane formation (​link​)
Dew Point
We looked at the dew points of our surface weather map data plot for September 20, 2016 and
compared Miami, Florida’s dew point and Canada’s dew point. We observed that Canada had the
highest relative humidity because its temperature was the same as its dew point. This means that
Canada had a 100% relative humidity. In contrast we observed that Miami had the lowest
relative humidity because there was a big difference between its temperature and dew point. The
higher the dew point the greater number of water vapor molecules there are.
Atmosphere and Pressure
We reviewed the infographic (​link​) comparing stacks of bricks to stacks of air parcels. A
barometer (device that measures pressure) works the same way a weight scale does, by
measuring the weight (or pressure) above it.
Pressure is a measure of the total weight of the atmosphere above the level at which it’s
measured. The conventional unit of pressure used by meteorologists is the millibar. The weight
of the atmosphere is 1000 millibars.
The air and ocean are analogous, so scientists had to come up with a way to measure portions of
them. Meteorologists divide the atmosphere into columns to visualize the “air parcels”, which
are an arbitrary size. The air parcels are measured in millibars (mb) with sea level being around
1000mb of atmosphere. To compare, planet Mars only has 5-20mb of atmosphere, which is 2%
of the Earth’s atmosphere. On Mars the surface pressure is 5 millibars during the winter and 20
millibars during the summer.
The top of our atmosphere (where the pressure is 0mb) is 600km (400mi) from the Earth’s
surface and 99% of weather occurs in the bottom 80%. Half of the atmospheric pressure occurs
below 6km (18,000ft). This is called the 500mb level. It is at this level that we can see the
movement of clouds.
We viewed the vertical limit image and talked about the decrease in oxygen in high places due to
a decrease in atmospheric pressure. The top of Mount Everest has a pressure of 300 millibars.
We also talked and examined a picture of the troposphere. The Troposphere is the lowest layer of
Earth’s atmosphere with its top being called the Tropopause.
All weather occurs in the Troposhepere (​link​) which is from sea level to 9000m (36,000ft) up
into the atmosphere. In order to avoid weather, planes cruise near the top of the Troposphere,
about 34,000ft.
We looked at the Pressure Decrease infographic (​link​) to illustrate the pressure at various
altitudes. Then we reviewed atmospheric pressure definitions (​link​).
Homework Review
Looked at Hurricane Pain in relation to Map #1 in homework
Scientific Method is a way to discern patterns in nature. The track of hurricanes is usually
narrow and widens as it travels across the ocean. This phenomena is tied to ocean surface
temperatures.
The ocean surface temperature near Baja Ca is 28⁰C (82⁰F), while the northern temperatures
along the coast are colder. Since 28⁰C is the optimal temperature for hurricanes, as hurricane
Pain moves north, it weakens from the colder temperatures.
Possible connection to global warming and disasters from hurricanes: if the temperatures along
the CA coastline increase to 28⁰C, hurricanes will survive longer as they move north, creating
more disasters.
Streamline & Isobar Handouts ​(​link​) (​link​)
Isobars are contour lines on a weather map that indicate areas of equal pressure, labeled in whole
millibars and drawn every 4mb. Sometimes the lines make concentric patterns, which usually
indicate an area of higher or lower pressure than the areas surrounding it.
Definitions of Streamline Fronts:
Warm Front: a boundary where warm air streams are colliding with colder air, indicated on the
map with red semicircles pointing to where the warm air is moving.
Cold Front: a boundary where cold air streams are colliding with warmer air, indicated on the
map with blue triangles pointing to where the cold air is moving.
Stationary Front: a boundary where both cold and warm air streams are colliding, indicated with
a combination of blue triangles and red semicircles.
We looked at satellite images to connect rainfall to the streamline handout, showing that there
was heavy rainfall in Oklahoma City where there was a Stationary Front. In Portland, ME there
was some rain from the warm front.