Weather and Climate

1
Introduction to GeographyPeople, Places, and
Environment, 4eEdward F. BergmanWilliam H.
Renwick

• Chapter 2
• Weather and Climate
• Victoria Alapo, Instructor
• Geog 1010

2
Weather and Climate

• Weather
• Day-to-day variations in temperature and
  precipitation. Examples temporary storms,
  temperature changes.
• Climate
• Statistical summary of weather conditions over
  several decades or more, but usually 30 yrs.
• Thirty years was chosen as a period long enough
  to eliminate year-to-year variations.
• Source http//www.metoffice.gov.uk/climate/uk/ave
  rages/

3
Intensity of Solar Radiation (Insolation)

• Affected by
• Angle of incidence more vertical at the
  equator. Oblique towards the poles.
• Also, axial tilt 23.5 degrees.

4
Latitude

• Summer Solstice June 20 or 21
• Longer days In the northern hemisphere
• Winter Solstice December 20 or 21
• Longer nights in the northern hemisphere
• But in the southern hemisphere, the opposite is
  occurring on both days! (June Dec)
• Equinoxes
• (equal day/night) see next slide.
• Vernal/Spring Equinox March 20 or 21
• Autumnal Equinox Sept. 20 or 21

5
(No Transcript)
6
Greenhouse Effect

• Explain the Greenhouse Effect
• Greenhouse gases
• Water vapor, carbon dioxide, ozone, methane
• Increased greenhouse gases increased global
  warming

7
Relative Humidity

• Water content of air it measures the wetness of
  air.
• Its also the percent () of water air could hold
  at a given temperature (as seen on TV).

8
Precipitation 3 Types (ways it forms)

• (1) Convectional precipitation
• Warm, humid air rises, and cools
• Saturation point is reached
• Clouds form
• Leads to convectional storms

9
(No Transcript)
10
(2) Orographic Precipitation

• Wind forces air up and over mountains
• Rain on windward side
• Desert on leeward side Rain shadow
• Examples
• The Rockies and Sierra Nevada. Also, see picture
  on pg 55, and caption.

11
(No Transcript)
12
(3) Frontal Precipitation

• This happens when air is forced up the boundary
  between cold and warm air masses (called a
  front).
• Cold front
• When cold air mass moves towards warm air mass
• Warm front
• When warm air mass moves towards cooler air mass
• See animation

13
(No Transcript)
14
Circulation Patterns

• Air mass 14.7 lbs per square inch.
• Air has weight! Think of a cylinder of
  propane/oxygen.
• Atmospheric pressure
• Varies with altitude
• Higher altitude less atmospheric pressure
• Thats why your ear pops as the pressure
  increases on descent in an airplane.
• Barometer instrument for measuring pressure.

15
Pressure and Winds

• Coriolis Effect
• An apparent deflection of any freely moving
  object from its expected (straight) path, caused
  by the Earths rotation. The earth rotates from
  west to east.
• Causes winds to move in an indirect, curving
  path, including hurricanes, and ocean currents,
  see next slide. If the earth did not move
  (rotate), winds would just move in a straight
  line from high pressure to low pressure.
• Happens to planes too, esp. when traveling in a
  straight line from the north pole to the equator.
  Thats why pilots fly in a curve. Otherwise,
  theyll land to the west of their intended
  destination. See animation.

16
Ocean Circulation Patterns

• Gyres is the special name ocean currents are
  called.
• These are wind-driven circular flows.

17
Coriolis Effect
18
Global Circulation
19
Global Circulation

• Only 3 of these zones will be discussed
• A) Inter-tropical convergence zone (ITCZ)
• This is where the N/E S/E winds converge. See
  previous slide. These converging winds are also
  called Trade Winds, because they were important
  to sailing ships.
• B) Subtropical high-pressure zones
• These are areas of dry, bright sunshine, and
  little precipitation. They cause deserts. It is
  an area of warm dry air found about 30 degrees N
  S latitudes. See next slide.

20
Subtropical Highs
Responsible for the worlds greatest deserts. Dry
conditions caused by no uplift of air due to high
pressure.
21
Global Circulation

• C) Polar high-pressure zones
• The intense cold causes dense air because
  coldness causes contraction, and so there is
  little molecular space, therefore air cant lift.
  This causes high pressure.
• As a result, the air stays close to the ground
  and there is little precipitation, leading to
  polar deserts. Polar deserts are typically
  drier than hot deserts see climograph of
  McMurdo, Antarctica.

22
Storms

• Cyclones
• These are low-pressure systems
• There are 2 types
• A) Hurricanes (N/America) and Typhoons (Pacific)
• Also known as tropical cyclones
• B) Midlatitude cyclones tornadoes, Box on pg
  66.

23
Storms

• Hurricanes/ Typhoons
• Need warm, moist air
• Most powerful over oceans (occur more during
  summer).
• Once the winds reach 74 miles/hr they are called
  hurricanes/typhoons.
• They cause storm surges
• This is when there is an elevated sea level in
  the center of the storm. i.e. high waves
  crashing inland (e.g. Katrina). 90 of people
  die from this.

24
World Precipitation
2 primary measures of climate are Temperature
Precipitation
25
Classifying Climate

• The Köppen System
• It is the most widely used system and was
  developed by Wladimir Köppen in 1918.
• He used the distribution of plants to help draw
  boundaries btw climate regions (because
  vegetation types tend to closely follow
  precipitation and hence temperature in area). So
  these 3 are interrelated.
• Köppen identified 5 basic climate types, and
  subdivided them further to reveal important
  distinctions. See page 74 75 of text and next
  slide. An American Professor added the H Climate
  (Mountains)
• These classifications allows analysis and
  planning by geographers, govts, etc.

26
(No Transcript)
27
Climate Regions

• As the map shows, these regions are horizontal
  bands based on latitude. Read about each
  climatic region (A to E) on your own. Pages 76 to
  86.
• Sometimes climatologists use climographs to show
  temp and precipitation for every month of the
  year. Every climatic region and every city in the
  world has one. Draw a simple one for the test.
• The one on next slide is for Lanzhou, China (pg
  79).
• Also see website for Omaha climograph
• http//www.hprcc.unl.edu/stations/index.php?action
  metadatanetwork_station_id256255

28
Omaha Eppley Station Data http//www.hprcc.unl
.edu/stations/index.php?actionmetadatanetwork_st
ation_id256255
29
Climate Change

• The earth has alternated btw warm cold periods
  over time.
• 3 hypotheses reasons given for climate change
• Astronomical
• Sunspots relatively cool regions on the surface
  of the sun, which varies in , in a cycle lasting
  11 yrs.
• Geologic
• Volcanic eruptions large amts of dust gases
  can be ejected to reduce solar radiation, and
  cool the earth. E.g. Krakatau, Indonesia.
• Human
• Atmosphere increase in CO2 in the atmosphere
  since the start of the industrial revolution in
  the 18th century. CO2 is a greenhouse gas.
• Vegetation clearing