What is Weather?

Weather = the state of the atmosphere at some specific time and place.

 

What is the difference between weather and climate?

Climate is weather averaged over the long term (typically 30 years) for a specific region and also includes extremes; weather is very local and instantaneous.

 

What are the Ingredients for Weather?

In summary, there are at least 5 ingredients that result in weather, as we know it:

Sun / Solar Radiation

Atmospheric Circulation

Water Vapor

Rotation of the Earth

Land forms and Oceans

Solar radiation interacts with Earth’s atmosphere and its energy is absorbed by water vapor fuels cloud formation and drives storms.

 

Earth’s annual motion around the Sun results in the seasonal weather changes; the weather takes place exclusively in the lower part of the atmosphere known as the troposphere.

 

Solar heating heats the ground, which heats the air above it warmed air rises and is replaced by cooler air warm air aloft migrates north and cools, then sinks circulation cell is set up the Earth’s rotation provides the stage for the Coriolis effect to break up the circulation into three cells per hemisphere continents further modify the resulting circulation.

We are interested in certain physical properties of the Earth’s atmosphere, which we can measure in certain ways.

The fundamental properties of the atmosphere versus measurables:

Fundamental Property

Corresponding Measurable

Heat energy Temperature Density Pressure

Large scale motions Wind Velocity and Direction

Water vapor concentration

Dewpoint / Relative Humidity

Liquid and solid water in clouds and precipitation

Cloud height, cover, visibility and precipitation

Atmospheric Origin, Composition, and Structure

* * * * * * * * * * * * * * * * * * Atmosphere, Weather, and Climate   The Earth’s atmosphere is a thin envelope of gases and suspended solid and liquid particles; the lowest 80 km (50 miles) is sometimes referred to as the homosphere and contains the same relative proportion of nitrogen to oxygen.•Climate averages are done over 30-year spans, beginning with the first year of a decade. For 2001-2010, the reference is the average over the period 1971-2000. Average high-low temperatures, precipitation, sunshine, etc. are included in the climate averages. •Also included are extremes in climate: high and low temperatures, 24-hour precipitation totals, monthly precipitation totals, etc.

 Evolution of the Atmosphere• Based on studies of other planets in the solar system and the analysis of

meteorites, rocks, and fossils, scientists have pieced together a picture of how the atmosphere came to be:

• The primeval phase was thought to have lasted from about 4.4 billion years ago (the Earth formed about 4.6 billion years ago) until about 1.5 billion years ago when the atmosphere as we know it was in place

• The earliest atmosphere, formed by outgassing (review the overall scheme of the formation of the earth…) was composed mostly of hydrogen and helium, with some ammonia and methane. This early atmosphere eventually escaped into space (why?) leaving a mostly CO2 atmosphere with some water vapor

and nitrogen.

• Over the eons, the atmosphere changed and evolved: the atmospheric CO2

was eventually washed out of the atmosphere and locked into the rocks, living organisms produced O2 by photosynthesis and removed more CO2.

• N2, being inert chemically, continued to be poured into the atmosphere via

outgassing, the O2 became a major component of the atmosphere and

eventually formed the protective ozone (O3) shield.

• Eventually, the atmosphere entered its modern phase, consisting of the elements in roughly the same abundances as we find them today

These gases composing the dry air in the lower atmosphere include (Table 2.1 of the text, p. 19):o Nitrogen (N2) 78.08%

o Oxygen (O2) 20.95%o Argon (Ar) 0.93%o Carbon dioxide (CO2) 0.0369%o Neon (Ne) 0.0018%o Helium (He) 0.00052%o Methane (CH4) 0.00014%

o Ozone (O3) 0.000007%

• Pollution: an air pollutant is a gas or aerosol (suspending solid or liquid particles) that occurs in a concentration that threatens the well-being of living organisms (especially humans) or disrupts the orderly functioning of the environment

o What are some familiar forms of pollution?o Many of these substances occur in the atmosphere naturally, but if their

concentrations exceed the tolerance limits of living organisms, they are referred to as pollutants

o Both human activities and natural processes (fires, volcanoes) are sources of pollutants

 Investigating the Atmosphere / Temperature Profile of the Atmosphere

• Meteorology is simply the study of the atmosphere. • A scientific model represents, approximately, something in nature

and comes in four forms: conceptual, graphical, physical, or numerical. Models commonly used in meteorology include weather maps and global climate models.

• Weather occurs in the lowest layer of the atmosphere, referred to as the troposphere. All clouds and weather occur in this 10-16km thick layer of gases.

• The atmosphere is divided into four principle layers, based on its vertical temperature profile: Troposphere, Stratosphere, Mesosphere, and Thermosphere.

 The Ionosphere and the Aurora• The Ionosphere is located mainly within the thermosphere and is composed of a

relatively high concentration of charged particles such as ions and elections.• Radio waves are reflected off the ionosphere, making long-distance

communication possible. • The aurora also occurs in the ionosphere, it has a base of about 100 km (62 mi)

and can extend upwards to 400 km (250 mi) or higher.• The aurora results from trapped electrons and protons being guided into the

atmosphere near the magnetic poles; these charged particles interact with those of the upper atmosphere, producing the luminous displays that come in many forms

• The aurora can take on many colors, but green and red are the two most common. Oxygen is responsible for these two colors: green-yellow wavelength of 557.7 nm is most common, while the deep red 630.0 nm light is seen less frequently.

• Nitrogen in an ionized state will produce blue light, neutral nitrogen molecules create purplish-red colors.

Monitoring the Atmosphere• Since the invention of the first weather instruments in the

17th century, weather monitoring has evolved:o Networks for monitoring the weather have become densero Instruments have become more sophisticatedo Communication systems have become bettero Observers better trained provide better datao Progress realized in surface and upper air observations

• Surface weather monitoringo Weather recording began in the 17th and 18th centuries and have

continued until this dayo National Weather Service Offices, 115 of them, established

across the country supported by some 1700 automated weather stations (Automated Surface Observing System=ASOS) used in weather forecasting and aviation.

o Doppler weather radar installed at 113 locations across the nation

Monitoring the Atmosphere, Continuedo Another 8000 cooperative weather stations are scattered across the

country these are manned by volunteers who monitor instruments provided by the NWS. Principle function to record daily precipitation and maximum / minimum temperatures for hydrologic, agriculture, and climatic purposes.

• Upper air observationso Kites used in the 18th century to get data a few hundred feet off the

ground; this was raised to nearly 30,000 feet in the 19th century.o Instruments used in upper air observation include radiosondes, small

instrument packages equipped with radio transmitters, carried aloft by balloons, taking measurements of the atmosphere as it goes.

o Radiosondes are launched simultaneously at 12-hour intervals (0000Z and 1200Z) from hundreds of ground stations around the world, these take data up to altitudes of 30,000 m or 100,000 feet.

Monitoring the Atmosphere, Continuedo A dropwindsonde is similar to a rawinsonde (a

radiosonde whose movements are tracked by radar to find variations in wind direction and speed) except it is dropped from an aircraft and radios back data every few seconds. These are used over the ocean and in storms such as hurricanes

o Weather satellites offer a broad and nearly continuous field of view. They image in several wavelengths and are capable of monitoring cloud patterns, temperature, water vapor concentrations, upper-air winds, rainfall; and can also make vertical profiles of atmospheric temperature and humidity.

Program note: discussion of conversion of energy from one form to another. The Earth system operates because it is able to convert one form of energy into another…some everyday examples will be given.

Weather ForecastingWorking with the Weather = Meteorology• The basic process for weather forecasting is based on numerical weather

prediction. The process they use in weather forecasting is as follows:– Weather data (observations) are collected from various locations and input to

computers for modeling. – A computer model is used, which consists of a system of mathematical equations

describing fluid motions.– Grid points are set up from the surface to the upper stratosphere; these points

describe the atmosphere at these points.– Each point has initial values of temperature, pressure, wind velocity and direction, etc.

derived from actual observations.– The relationship between these variables and equations are used to step the model

forward a small step at a time.– The model is run forward in time to obtain model data for forecasts.– The output consists of quantities for each grid point projected into the future (i.e. the

model data) and the initial outputs are compared with actual observations – Several models exist (e.g. the eta, the nested grid model, the aviation model, the

European / UK models, etc.) which vary slightly from one another. – Meteorologists study the output of these models, compare them with recent observed

trends, draw upon their experience and intuition and prepare forecast products for a certain region, which are updated three to four times daily.

– Forecasts are produced for government, industry, and the public.

Surface pressure patterns result in winds as air tends to move from areas of higher relative pressure to areas of lower relative pressure.

 Items of interest to meteorologists making forecasts:

Clouds and Precipitation patterns, temperature, humidity and dewpoint, the jet stream and steering currents. These quantities are measured at set times and are used in the weather forecasting process.

 ASOS = Automated Surface Observing System, a

network of stations that operate automatically to gather weather data on a continuous basis.

Sources of Weather Information• From experiences of everyday life, we all have a basic

understanding of weather and the atmosphere.• Sources of weather information and forecasts include

television, The Weather Channel, newspaper, the Internet, standard AM/FM radio, and the NOAA weather radio

Weather Systems and Weather Maps• Weather maps are constructed from observations

gathered from many reporting stations. Weather features are defined by patterns in the temperature, wind, pressure, and other quantities.

Weather maps and what they represent• Weather maps are constructed from observations

gathered from many reporting stations. • Weather features are defined by patterns in the

temperature, wind, pressure, and other quantities.• An air mass is a huge volume of air covering hundreds of

thousands of square kilometers that is relatively uniform in its horizontal temperature and relative humidity distribution. Specific properties of an air mass depend on where it formed, what sort of terrain it traveled over, etc. An air mass can either be cold and humid, cold and dry, warm and humid, or warm and dry.

• A front is a narrow transition zone between airmasses that differ in temperature, humidity, or both. They usually come out of low-pressure systems. They can either be cold, warm, stationary, or occluded, depending on the relative properties of air behind the front.

• Low-pressure systems, known as cyclones, are characterized by rising air, which expands and cools, and becomes saturated. As a result clouds, and possibly precipitation form. The surface air around a low moves in a counterclockwise direction in the northern hemisphere and spirals inward.

• High pressure areas, or anticyclones, are generally fair-weather systems, characterized by sinking air which heats up and vaporizes condensates no clouds, dry. Air moves clockwise and spirals outward from a center of high pressure in the northern hemisphere.

Tools of the Weather Forecaster

Many such tools exist in the toolkit of the meteorologist, but two are highlighted briefly below.

Satellite imagery usually is provided in three forms:• Visible image—reflected sunlight illuminates the Earth to

provide the image and is only useful on the day side.• Infrared image—emitted light, can be used day or night,

and are presented such that the brighter the cloud, the colder, and higher, its top is.

• Water vapor—samples the concentration of water vapor between 5000 and 12,000 meters, brighter regions denote higher concentrations of water vapor.

 Weather Radar• Weather radar is useful for finding and tracking areas of

precipitation. It works by sending out pulses of microwave radiation, some of which is reflected back to the radar by rain, snow, insects, particulates, etc. in the atmosphere. The echoes of the radar are color coded to represent intensity. Radar works in two modes:

• Reflective mode, as described above, which maps the area and intensity of precipitation. Time-lapse movies can be constructed to show the movement of these areas.

• Doppler mode, used to find the line-of-sight velocity of an area of precipitation. Rotating thunderstorm cells, indicative of potential tornadic development, can easily be discerned with Doppler radar. In so doing, warnings can be issued relatively early, allowing time for people to take shelter.

 Sky watching• Clouds are visible products of condensation. They form

when unstable air starts moving vertically (convection), expands and cools, and becomes saturated. Saturated air is generally cloudy air.

• In contrast, stable air inhibits vertical motion, hence no cloud formation.

• Clouds are made up of tiny water droplets, ice crystals, or both. Clouds form when the relative humidity reaches 100%.

• Cloud droplets need tiny solid particles, aerosols, to condense on—many of these aerosols have an affinity (is attractive) to water.

• Clouds are classified by their general appearance Cirriform, stratiform, cumuliform.

Characteristics: Cirriform cumuliform stratiformAltitude of base- high middle lowTemperature cold warm warmComposition ice crystals water droplets water droplets

 • Precipitation comes principally from nimbostratus and

cumulonimbus.•  Collision-coalescence is the name of the process that forms

rain drops.• The Bergeron-Findeisen process is how frozen precipitation

(sleet, snow) is made.• Fog is a stratus cloud in contact with the ground. Drizzle

comes from stratiform clouds.

What is Space Weather?What is Space Weather?

• Today’s presentation is at (network-permitting):

• http://science.nasa.gov/ssl/pad/sppb/edu/

• Essentially, space weather deals with the conditions in interplanetary space that affects the Earth environment

• The domain covered by space weather stretches from the Sun to the Earth, and beyond.

Cognitive Skill of the Week: Explanation Explanation is a logical statement of understanding

regarding the reason(s) for or cause(s) of something. One example of this is the ability to provide a logical explanation of the relationship between atmospheric circulation and cold and warm air advection.

 Affective Attribute of the Week: Reasoning with

confidence A learner reasons with confidence when he or she reaches

a conclusion that follows from a logical path of inquiry that is guided by scientific understanding. As you do the homework and attend the lectures, you will develop a confidence in understanding the nature and importance of air mass advection and through reasoned analysis will be able to locate areas of cold and warm air advection based on patterns displayed on a weather map.