Is air moving away or towards each of these pressure centers? Bellwork 4/12 H L Is air moving away or towards each of these pressure centers? Will air circulate Clockwise or Counterclockwise around each of these pressure centers?

Cyclonic and anticyclonic winds in the Northern Hemisphere

Cyclones and anticyclones A center of low pressure Pressure decreases toward the center Wind blow inward and Counterclockwise around a low (Northern Hemisphere) **CONVERGING winds Forces air upwards Rising air = cloud formation

Cyclones and anticyclones A center of high pressure Pressure increases toward center Winds around a high blow outward and clockwise (Northern Hemisphere) **DIVERGING winds Causes air to sink Sinking = little/no cloud formation… “Fair weather”

Cyclones and anticyclones Cyclones exist for long periods of time only when air aloft is diverging Maintains low surface pressure Anticyclones exist for long periods of time only when air aloft is converging Maintains high surface pressure Diagram on next slide

Airflow associated with surface cyclones and anticyclones

How to read a weather map:

Symbols

Wind Directions

Quick Practice: 1. Locate the weather station in northern Iowa. From which direction is the wind blowing? 2. Locate the weather station in Chicago, Illinois. From which direction is the wind blowing? 3. Locate and label any Highs or Lows on this map. 4. Cyclones are associated with which type of system? 5. Anticyclones are associated with which type of system?

Which way is the wind blowing?

General atmospheric circulation Underlying cause is unequal surface heating *Much is still unknown about global circulation, but it helps to start by looking at a non-rotating Earth…

Circulation on a Non-rotating Earth There would be two “cells” that distribute heat One moving warm air to the poles, One moving cool air the equator …but our Earth rotates…

Idealized global circulation

General atmospheric circulation Idealized global circulation 4 Pressure Systems associated with air distribution Equatorial Low Pressure Zone Subtropical High Pressure Zone Subpolar Low Pressure Zone Polar High Pressure Zone

Pressure Systems Equatorial Low pressure zone Rising air Abundant precipitation Subtropical High pressure zone Subsiding, stable, dry air = deserts Air traveling equatorward from the subtropical high produces the trade winds Air traveling poleward from the subtropical high produces the westerly winds

Pressure Systems Subpolar Low pressure zone Polar High pressure zone Warm and cool winds interact creates a Polar Front – an area of storms Polar High pressure zone Cold, subsiding air Air spreads equator-ward and produces Polar Easterly winds Polar easterlies collide with the Westerlies along the Polar Front

Idealized global circulation

General atmospheric circulation Influence of continents Seasonal temperature differences disrupt the Global pressure patterns Global wind patterns Influence is most obvious in the Northern Hemisphere WHY??? _____________________ Monsoon Seasonal change in wind direction

General atmospheric circulation Influence of continents Monsoon Occur over continents During warm months Air flows onto land Warm, moist air from the ocean Winter months Air flows off the land Dry, continental air

Average surface pressure and associated winds for July

Average surface pressure and associated winds for January

Homework: http://earth.nullschool.net/#current/wind/surface/level/orthographic=-246.32,7.80,338 Identifying Winds & Pressure systems Applying your knowledge to make weather predictions

Bellwork 4/13 Why are deserts hot & dry? Why are rainforests warm & rainy? What connection can you make to wind patterns?

Surface Winds vs. Winds Aloft Upper air winds Generally blow parallel to isobars – called geostrophic winds (No effect from friction) Jet stream "River" of air High altitude High velocity (120-240) kilometers per hour

The geostrophic wind

Surface Winds vs. Winds Aloft Winds Below 600m Affected by friction Lowers wind speeds, which in turn lowers the Coriolis Effect

Comparison between upper-level winds and surface winds