AOSS 401 Geophysical Fluid Dynamics Atmospheric Dynamics Prepared

AOSS 401 Geophysical Fluid Dynamics: Atmospheric Dynamics Prepared: 20131010 Climate, Weather, Geography, Earth Richard B. Rood (Room 2525, SRB) rbrood@umich. edu 734 -647 -3530 Cell: 301 -526 -8572

Class News • Ctools site (AOSS 401 001 F 13) • First Examination on October 22, 2013 • Second Examination on December 10, 2013 • Homework posted: – Ctools Assignments tab – Due Thursday October 10, 2013 – Derivations (using notes)

Weather • National Weather Service – Model forecasts: • Weather Underground – Model forecasts: • NCAR Research Applications Program

Outline • Tour of the Earth – Geography – Planet – Physics

Building the Radiative Balance Redistribution by atmosphere, ocean, etc. Top of Atmosphere / Edge of Space RS 1) The absorbed solar energy is converted to terrestrial thermal energy. CLOUD SURFACE 2) Then it is redistributed by the atmosphere, ocean, land, ice, life. ATMOSPHERE

Another important consideration Latitudinal dependence of heating and cooling Top of Atmosphere / Edge of Space CLOUD ATMOSPHERE After the redistribution of energy, the emission of infrared radiation from the Earth is ~ equal from all latitudes. Because of tilt of Earth, Solar Radiation is absorbed preferentially at the Equator (low latitudes). SURFACE South Pole (Cooling) Equator (On average heating) North Pole (Cooling)

Transfer of heat north and south is an important element of the climate at the Earth’s surface Redistribution by atmosphere, ocean, etc. Top of Atmosphere / Edge of Space This predisposition for parts of the globe to be warm and parts of the globe to be cold means that measuring global warming is difficult. Some parts of the world could, in fact, get cooler because this warm and cool pattern could be changed. CLOUD ATMOSPHERE heat is moved to poles cool is moved towards equator SURFACE This is a transfer. Both ocean and atmosphere are important!

Scientific Method • What follows are a series of pictures, plots, graphs – mostly of observations. As we go through them think first – How do I describe the picture? – What type of behavior might be represented? Patterns, correlations – How might I investigate this behavior? • Scientific investigation is based first on observations.

Long as I remember the rain been comin’ down [from the National Atlas (1970)] (1930 -1961) Grange, October 2006

Ocean Surface Currents (From Steven Dutch, U Wisconsin, Green Bay) Good Material at National Earth Science Teachers Association

The Thermohaline Circulation (THC) (Global, organized circulation in the ocean) (The “conveyer belt”, “rivers” within the ocean) Blue shading, low salt Where there is localized exchange of water between the surface and the deep ocean (convection) Green shading, high salt Warm, surface currents. Cold, bottom currents.

Transfer of heat north and south is an important element of the climate at the Earth’s surface. Redistribution by atmosphere, ocean, etc. Top of Atmosphere / Edge of Space Large scale weather systems transport large quantities of thermal energy from equator toward the poles CLOUD ATMOSPHERE heat is moved to poles cool air moved towards equator SURFACE This is a transfer. Both ocean and atmosphere are important!

Tropospheric Mean Meridional Circulation This is not exactly physical, but is a common conceptual model.

Dynamic atmosphere: Hurricanes --- Vortices • Satellite image • Storm that originates over warm ocean water • Scale of the motion: 1000 km

Hurricanes and heat Sea Surface Temperature (blue cool / warm orange)

Hurricanes and heat

Mid-latitude cyclones - waves

Mid-latitude cyclones & Heat

What goes on vertically?

Some basics of the atmosphere Troposphere --------- ~ 2 Mountain Troposphere --------- ~ 1. 6 x 10 -3 Earth radius Troposphere: depth ~ 1. 0 x 104 m This scale analysis tells us that the troposphere is thin relative to the size of the Earth and that mountains extend half way through the troposphere.

An estimate of the January mean temperature mesosphere stratopause note where the horizontal temperature gradients are large stratosphere tropopause troposphere south summer north winter

An estimate of the January mean zonal wind note the jet streams south summer north winter

An estimate of the July mean zonal wind note the jet streams south winter north summer

Let’s spend some time with the atmosphere. • Start with a typical upper tropospheric chart. • What is a good estimate of the pressure at the surface? • What is a good estimate of the pressure in the upper troposphere? • How could you figure out the geometric height?

Geostrophic wind 300 h. Pa How does this example relate to global scales?

300 h. Pa

Geopotential contours at 300 h. PA Northern Hemisphere September 17, 2008

Wind and geopotential 200 h. Pa Note: Variability in east -west of the wind field. Note: Time variability of the wind field. Note: Troughs associated with mountain ranges, continents

Geopotential contours at 850 h. Pa Northern Hemisphere September 17, 2008

700 h. Pa

500 h. Pa

300 h. Pa

50 h. Pa

North-south / Winter-summer

DJF 500 h. Pa Average

JJA 500 h. Pa Average

Anomaly 100 h. Pa

23 October 2006, Geopotential Height

23 October 2006, Ozone

Take Away Points • The details of the Earth’s relation to the Sun, energy received, tilt of axis, variations in orbit set up gradients of temperature (energy) in a fluid (atmosphere and ocean), and the fluid moves to reduce these gradients. – Composition of atmosphere and ocean important to the energy distribution • The distribution of land water, mountains, plants, etc. are fundamental to climate and weather. • The rotation of the Earth is a defining characteristic of the motions of the atmosphere and ocean.

Take Away Points • Motion in the atmosphere and ocean is often described as types of features – notably: – Waves – Vortices • We can “isolate” and study; diagnose balances of momentum, mass, and energy; predict behavior of these features with significant skill – The interactions between all of these “isolated” features is far more difficult to study quantitatively and at the center of how energy is ultimately re-distributed.

Summary of Take Away Points • The patterns of weather and climate that we see are not random or accidental. – Basic redistribution of energy – Determined by characteristics of Earth – especially relation of Earth to Sun and rotation – Determined by geography – Determined by surface energy characteristics – Chaos?