EES 125 Chapter 1 Notes 8-18-22

8-18-22

There have been monumental advances in monitoring of weather over time. The January 2016 snowstorm rated a rare “extreme” for the NE US.
The deadliest blizzard on record for the American prairie was the Blizzard of ‘88. It is often referred to as the Children’s Blizzard.
Today, though not exact, we are much better at monitoring and forecasting weather through understanding of coastal winter storms, satellites/radar, radiosondes, and surface observations.
A nor’easter is a powerful coastal storm that tracks offshore, parallel to the Atlantic coast, and is named for the strong Northeast winds that affect coastal areas.

NOAA stands for the National Oceanic and Atmospheric Administration.

Weather- state of the atmosphere at some place and time. It’s described with quantitative variables (temperature, humidity, cloudiness, precipitation, wind speed, and wind direction).

Meteorology is the study of the atmosphere, the processes that cause weather, and the life cycle of weather systems.

Climate- weather conditions at some locality averaged over a specified time period. Climate is averaged weather, computed for the last 30 years and updated every decade. A locale’s climate also includes weather extremes.

Climatology is the study of climate, its controls, and spatial and temporal variability.

The definition of climate has expanded to describe the state of Earth’s climate systems as a whole. It results from internal and external influences, mutual interactions, and feedbacks.
Water vapor along with CO2 are major greenhouse gases (GHGs).

To assess weather information, we use smartphones, online sources, television (The Weather Channel and local newscasts), and radio. Radio includes NOAA Weather Radio, which has continuous broadcasts repeated every 4-6 minutes. Time zones are measured east/west of the prime meridian (0 degrees longitude).

Earth makes one complete rotation (360 degrees) every 24 hours. Hence, Earth rotates through 15 degrees of longitude every hour. So the Earth should be divided into 24 civil time zones.

UTC (Universel Temps Coordinne) is based on an atomic clock, expressed as a 24-hour clock. There is no Daylight Savings Time in this system. Basically, Z time, GMT, and UTC are equivalent. Surface observations are taken at least 4 times per 24 hours, and the US takes hourly observations.

There are two types of pressure systems:
High and low air pressure. High pressure area is relatively high compared to surrounding air, called “anticyclones”. Low pressure area is relatively low compared to surrounding air, called “cyclones”. Lows are associated with RISING air and often bring clouds and precipitation.
High pressure systems prevent clouds from forming, while low pressure systems are unstable. Highs are often described as fair-weather systems. Lows are described as stormy-weather systems.

Air pressure is the weight per unit area of a column of air that extends upward from Earth’s surface (or any altitude within the atmosphere) to the top of the atmosphere.

Low pressure systems are counter-clockwise in the N Hemisphere (clockwise in the S Hemisphere) with pressure DECREASING towards the center and have an inward spiral. H__igh pressure systems__ are clockwise in the N Hemisphere and have an outward spiral with pressure INCREASING towards the center.

Winter storms are more likely to the west and north of the path of a low-pressure system.

Wind pressure systems aren’t perpendicular to the center due to the rotation of the Earth. Air Masses are huge volumes of air covering hundreds of thousands of square kilometers. They have relatively uniform characteristics horizontally, including temperature and humidity. They gather characteristics from a source region.

Cold, dry air masses form at higher latitudes over continents. Cold, humid air masses form at higher latitudes over maritime surfaces.
Warm, dry air masses form over continents in subtropical regions.
Warm, humid air masses form near the equator or in the subtropics over maritime surfaces.

Weather Radar complements satellite surveillance by locating and tracking the movement of areas of precipitation. Doppler radar detects movement, and is excellent for forecasting tornadoes.

Polar Air Masses are colder in winter, milder in summer. Tropical Air Masses have less seasonal variation due to nearly uniform sunlight, duration, and intensity. These masses modify as they move away from a source region, meaning they take on the characteristics of the area they pass over.

Cold Fronts are more likely to have thunderstorms and heavy rain. Fronts are transition zones between air masses that differ in temperature, humidity, or both.

Fronts are 3-dimensional. They form where contrasting air masses meet, and the associated air movements often give rise to cloudiness and precipitation. Where the front intersects Earth’s surface is shown with the front symbol on the map where the frontal surface intersects Earth’s surface.
Some fronts have no clouds or precipitation, and are stationary.The passage is indicated by wind shift and temperature/humidity changes.
Warm front clouds and precipitation occur over a wide band (usually 12-24 hours or longer), while cold front clouds and precipitation occur over a narrow band (only a couple minutes to hours, hard precipitation).

In Coastal areas, lake/sea breezes produce lower summer temperatures. It may push 10-50km inland from the shore.

In describing the state of the atmosphere, the maximum temperature usually occurs in early to mid-afternoon. The minimum temperature usually occurs around sunrise. The dewpoint (frost point) is the temperature when air is cooled, at constant pressure, so it’s saturated with water vapor and dew (frost) forms.

Relative humidity is the percentage/ratio of actual water vapor concentration of air vs. water vapor concentration if air was saturated. Relative humidity changes through the day as temperature varies. Generally, the highest is around sunrise and lowest when warmest (early to mid-afternoon).
Precipitation amount: general rule- 10 in. of snow equals 1 inch of precipitation.
Sky cover is the fraction of the sky that is cloud covered. An overcast sky prevents the day’s minimum temperature from falling and the day’s maximum from rising more than otherwise.

Weather watch is when hazardous weather is considered possible based on current or anticipated atmospheric conditions. Weather warning is when hazardous weather is happening, imminent, or has a high probability of occurring.

We describe the tendency of air pressure as rising or falling, and falling may indicate an approaching cold front. In terms of wind direction and speed, wind direction is the direction it blows from (west wind blows from the west and towards the east).

Weather Satellite Imagery includes geostationary and polar orbiting satellitesMost weather satellite images are obtained by sensors onboard a Geostationary Operational Environmental Satellite (GOES). A GOES satellite revolves around Earth at the same rate and in the same direction as the planet rotates so it’s always positioned over the same spot on Earth’s surface. The sub-satellite point (the location on Earth’s surface directly below the satellite) is essentially on the equator.

A Polar-orbiting Environmental Satellite (POES) travels in a north-south orbit passing close to the poles.
Satellite-borne sensors are either passive or active. Passive sensors measure radiation coming from the Earth-atmosphere system, both visible solar radiation reflected by the planet and invisible infrared radiation emitted by the planet. The two types of images produced are visible satellite images and infrared satellite images. Infrared can provide information anytime while satellite images are available only during daylight hours.
Warm objects emit more intense infrared (IR) radiation than cold objects.

Water vapor satellite images allow meteorologists to identify and track the movement of moisture plumes within the atmosphere over thousands of kilometers.

Clouds are aggregates of tiny water droplets, ice crystals, or some combination of both. Cirrus clouds, which are ice-crystal clouds, occur at high altitudes where air temps are relatively low; they have a fibrous or wispy appearance. Cumulus clouds are water-droplet clouds that occur at lower altitudes where temperatures are higher; their edges are more sharply defined.

Fog is actually a cloud that is very near or in contact with Earth’s surface.
Some clouds form in horizontal layers (stratiform clouds) while others appear puffy (cumuliform clouds). Stratiform clouds often develop ahead of a warm front while cumuliform clouds, especially those having great vertical development, form along or just ahead of a cold front.
Cumulus clouds build vertically and merge laterally, eventually forming a thunderstorm cloud (aka a cumulonimbus cloud).

8-23-22

Water vapor makes up about 4% of the air’s volume, and it forms clouds and precipitation. Water vapor also absorbs heat energy from Earth.
Ozone has three atoms of oxygen (O3) and its distribution is not uniform. It’s concentrated between 10 to 50 kilometers above the surface. Ozone also absorbs harmful UV radiation. However, human activity is depleting ozone by adding chlorofluorocarbons (CFCs).
Aerosols are tiny solid and liquid particles. Water vapor can condense on solids, and aerosols reflect sunlight. Aerosols are the reason we have color in sunrise and sunset. Methane traps more heat than CO2.
Sleet happens more in the winter while hail happens in the summer.

Condensation nuclei are what causes condensation to form.

Pressure changes: Pressure is the weight of the air above.

The average sea level pressure is slightly more than 1000 millibars (1,013.2), at about 14.7 pounds per square inch. Pressure decreases with altitude!

One-half of the atmosphere is below 3.5 miles (5.6 km), and 90% of the atmosphere is below 10 miles.

Force is exerted by the weight of the air above. The weight of the air at sea level is 1 kilogram per square centimeter. Inches of mercury are used to describe air pressure, and the standard sea level pressure is 29.92 inches of mercury.

Wind is the horizontal movement of air, out of areas of high pressure and into areas of low pressure.

Controls of wind:

Pressure gradient force
Isobars- lines of equal air pressure
Pressure gradient- pressure changes over distance
Coriolis effect
Apparent deflection in the wind direction due to Earth’s rotation
Deflection is to the right in the N Hemisphere and to the left in the S Hemisphere
Specifically, the Coriolis Effect means that once air has been set in motion by the pressure gradient force, it undergoes an apparent deflection from its path, as seen by an observer on Earth. As air moves from high to low pressure in the N Hemisphere, it is deflected to the right by the Coriolis force and left in the S Hemisphere.
Friction
Only important near the surface
Acts to slow the air’s movement

8-25-22

A barometer is an instrument for measuring pressure. The mercury barometer is a glass tube filled with mercury. An aneroid barometer is one “without liquid” that uses an expanding chamber. A barograph continuously records air pressure.

Upper air winds generally blow parallel to isobars, also known as jet streams.

Local winds are produced from temperature differences that are small scale winds. Types include land and sea breezes, mountain and valley breezes, and Chinook and Santa Ana winds.
Changes in wind direction are associated with the locations of cyclones and anticyclones. This often brings changes in temperature and moisture conditions.

The two basic measurements for wind are direction and speed:

Direction: here, winds are labeled from where they originate (e.g. North wind- blows from the north toward the south). The instrument for measuring wind direction is the wind vane. Direction is indicated by either compass points (N, NE, etc.) or a scale of 0 degrees to 360 degrees. Prevailing wind often comes from one direction.
Speed: is often measured by a cup anemometer.