Meteorology 10: Weather and Climate Lecture 1 Dr. Craig Clements San Jos é State University

Meteorology 10: Weather and ClimateLecture 1

Dr. Craig ClementsSan José State University

Jan 24, 2013

The term “meteorology” dates back to Aristotle’s classic text Meteorologica, written in 340 B.C.

At that time, “meteor” referred to any object in the sky, including raindrops and snowflakes. Centuries later, when researchers began to specialize in the study of extraterrestrial objects entering Earth’s atmosphere, the term “meteorology” had already found a home in the context of weather.

Thus, the science of what we now call meteors became known as meteoritics, and its practitioners meteoriticists.

(Henson, 2008)

What is Meteorology?

What is weather vs. climate?

• Weather: – the state of the atmosphere at a particular point in time.

• Climate:– the accumulation of daily or seasonal weather events

over a longer time period.

Meteorology and Climatology represent the study of weather and climate respectively, but are each components of Atmospheric Science and are dealt with in this course

Climate vs. Weather

Weather ClimateShorter-term fluctuations Longer-Term Changes

in atmospheric environment broad composite of average (or mean) (e.g., temp, press, ws, wdir, condition of a region (e.g., temp, rainfall, rainfall amount, etc) snowfall, ice cover, winds)

Hours, Days, Weeks Years (and longer)

Specific location for specific time Mean state of a specific region(e.g., continent, ocean, or entire planet)

Elements of Weather

• air temperature• air pressure• humidity• clouds• precipitation• visibility• wind

• Certain weather elements, likeclouds, visibility and wind, areof particular interest to pilots.

Composition of the Atmosphere

What is the Earth’s atmosphere composed of?

The earth’s atmosphere is comprised mostly of:

nitrogen (N2) and oxygen (O2),

with small amounts of other gases, called ‘trace gases’ such as water vapor (H2O) and Carbon Dioxide (CO2)

Table 1-1, p. 3

Composition of the Atmosphere

nitrogen (N2) = 78%oxygen (O2) = 21%

These gases are fairly constant up to 80 km (50 miles)

• Carbon dioxide and the greenhouse gases• ozone• aerosols• pollutants

• Ozone at high altitudes (stratosphere) is “good”;ozone at low altitudes (troposphere) is “bad.”

Composition of the Atmosphere

Other gases and stuff in the atmosphere are:

Composition of the AtmosphereCarbon dioxide (CO2)

Composition of the AtmosphereSources of Carbon dioxide (CO2)

What kind of pollutants are emitted from coal plants?

CO, CO2, SO2, NOx

The vertical structure of the earth’s atmosphere is complex

The atmosphere is composed of different layers

A View from Space. How deep is the atmosphere?

A Brief Look at Air Pressure and Air Density

• air density• air pressure• sea-level pressure

• Baseballs travel farther in higher-altitude air (Denver)than they do in lower-altitude air.

Air density (ρ) is the number of air molecules in a given volume (space). Air density is greatest at the surface and decreases with height (as we move up into the atmosphere).

Air molecules are held near the earth by gravity. This strong, invisible force pulling down on the air above squeezes (compresses) air molecules closer together, which causes their number in a given volume to increase.

Air density

Air molecules have weight. Air is surprisingly heavy. - The weight of all the air on earth is 5600 trillion tons.

The weight of the air molecules acts as a force on earth and us. The amount of force exerted over an area of surface is called atmospheric pressure or air pressure.

The pressure at any level in the atmosphere may be measured as total mass of air above any point.

If we weigh a column of air one square inch in cross section, extending from average height of ocean surface (sea level) to the top of the atmosphere, it would weigh 14.7 pounds.

Atmospheric pressure

Atmospheric pressure

If more molecules are packed into the column, the density then ___________ and the surface pressure __________.

On the other hand, when there are fewer molecules in the column, the air weighs _______and the surface pressure __________.

increases

less

increases

decreases

Most common units for atmospheric pressure are millibar (mb) and Hectopascal (hPa). Another unit used is inches of mercury (Hg).

At sea level, the standard value for atmospheric pressure is:

1013.25 mb = 1013.25 hPa = 29.92 in. Hg.

Atmospheric pressure

A barometer is used to measure atmospheric pressure and therefore, it is also referred to as barometric pressure.

Fig. 1-7, p. 8

Fig. 1-8, p. 9

Layers of the Atmosphere

Vertical temperature profileIndicates different layers:• troposphere• stratosphere• mesosphere• thermosphere

How do we measure the vertical structure of the atmosphere?

A radiosonde balloon ready to be launched by SJSU graduate student, Scott Strenfel, July 2008.

A weather balloon!

What layer in the atmosphere does ‘most’ of our weather occur?Troposphere!

Depth: surface to ~11 km (~36,000 feet) above the surface. This is where lots of mixing occurs due to rising and sinking air motions

Air cools with height (on average) in the troposphere. This is due to the fact that sunlight warms the surface of the earth and, in turn, warms the air above it.

The rate at which the air temperature decreases with height is called the temperature lapse rate.

The average lapse rate in the troposphere is 6.5 degrees Celsius (ºC) for every 1000 meters (m). This is approximately 3.6 degrees Fahrenheit (ºF) for every 1000 ft rise in elevation.

Stratosphere

Depth of the stratosphere is located above the troposphere from approximately 12 km to about 50 km.

Temperature increases with height in the stratosphere. This temperature structure (temperature inversion) helps keep mixing limited to the troposphere.

Temperatures in the stratosphere are cold, averaging less than -46°C.

The reason for the inversion in the stratosphere is that the ozone, which is fairly abundant in the stratosphere, absorbs (UV) solar radiation. Some of this absorbed energy warms the stratosphere.

Mesosphere

The air in the mesosphere (middle sphere) is extremely thin and pressure is low. While the percentage of nitrogen and oxygen in this layer is about the same as at the surface, there are fewer oxygen molecules here.

The mesosphere is located above the stratosphere from approximately 50 km to about 85 km.

Temperature decreases with height in the mesosphere.

Temperatures at the top of the mesosphere represent the coldest in our atmosphere, averaging -90°C!

Thermosphere

The layer above the mesosphere is the thermosphere “hot layer”.

The thermosphere is located above the mesosphere from approximately 85 km to 500 km.

Oxygen molecules in this layer absorb energetic solar rays which warm the air. Since there are few atoms and molecules the absorption of a small amount of solar energy can cause a large increase in temperature that may exceed 500°C!

It is in this layer that charged particles from the sun interact with air molecules to produce aurora displays.

Ionosphere

This layer is not really a separate ‘sphere’, but rather an electrified region within the upper atmosphere where fairly large concentrations of ions and free electrons exist.

A bulk of the ionosphere is in the thermosphere, 60 km and up.

An ion is an atom that has lost (or gained) one of more electrons. Atoms lose electrons and become positively charged when they cannot absorb all of the energy transferred to them by a colliding energetic particle.

The ionosphere plays a major role in AM radio communications.

When the radio was invented by G. Marconi in the early 20th century, it was not known how radio waves traveled long distances through the atmosphere.

Scales of Atmospheric Motion

Motion in our atmosphere occurs at multiple spatial scales. These range from large planetary waves to turbulence inside the class room due to air conditioning.

Typical scales of motion that we will be discussing in this course are:

1. Global scale: planetary waves, 5000 km2. Synoptic scale: cold fronts, air masses, hurricanes 2000

km 3. Mesoscale: thunderstorms, sea breeze, 20 km 4. Microscale: turbulence, winds around buildings, 2 m

Lets look at a weather Map

We need to understand a few things on a weather map.

First, when we talk about wind, we need to understand how we describe wind direction.

In meteorology, when winds are blowing from North to South we call that a north wind. If it blows from the west, we can that a west wind. Winds are referenced from where they are blowing from not to.

Lets look at a weather Map

Fronts are boundaries that separate different air masses.

A cold front is a boundary of cold air and a warm front is a boundary of warm air.

On a weather map, “L” represents low pressure while an “H” represents high pressure.

A view from a satellite in

space.

Hurricane Gustav: August 31, 2008

• Our class will use both English and Metric unit systems.

• Most important:– Distance (kilometres and miles) – Temperature (ºC and ºF)

• Conversions:1.6 km = 1 mile; 1 km = 0.61 miles(9/5 x ºC) + 32 = ºF(ºF – 32) x 5/9 = ºC

UnitsUnits

HW 1: Unit ReviewHW 1: Unit ReviewDue: Wednesday Sept. 8Due: Wednesday Sept. 8

(show all your calculations)

1.75.4°F to °C2.100°C to °F3.-40°C to °F4.-1°C to °F5. 10 km to miles6. 1 km to feet

Convert the following: