Skip to content
Quick Guides

Earth Science - Weather

Preview 10 of 36 pages

See the first 10 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Study Guide Earth Science – Weather 1. Moisture in the Atmosphere Most of Earth’s weather happens in the troposphere , the lowest layer of the atmosphere . Because all weather processes take place here, the troposphere is often called the “weather sphere.” 1.1 Why the Troposphere Is the Weather Layer The main reason the troposphere is the weather sphere is the presence of water vapor : • Water vapor is the source of clouds, rain, snow, and storms . • This layer contains nearly all of the atmosphere’s moisture . As a result, changes in temperature and air movement in the troposphere strongly affect daily weather. 1.2 What Happens Above the Troposphere? At the top of the troposphere is a boundary called the tropopause . • Above the tropopause , water vapor is essentially absent . • Without water vapor, weather processes do not occur in the higher layers of the atmosphere.

  2. Page 2
    Read page 2 as text

    Study Guide 1.3 Atmosphere Layers and Their Properties Each layer of the atmosphere has different: • Temperatures • Pressures • Amounts of water vapor These differences help explain why weather is limited to the troposphere. (A figure usually shows how temperature, pressure, and water vapor change from one atmospheric layer to another.) 1.4 Measurement of Water in the Air Water vapor is always present in the air, but the amount can change. Scientists use different measurements to describe how much water vapor is in the atmosphere . 1.5 Specific Humidity One way to measure moisture is called specific humidity . • It tells us how much water vapor is actually in the air . • Warm air can hold more water vapor than cold air . When air holds as much water vapor as it possibly can , it is said to be saturated . • As temperature increases, air’s capacity to hold water also increases. • In fact, this capacity doubles for about every 11°C rise in temperature . 1.6 Relative Humidity The measurement most commonly used is relative humidity . • Relative humidity compares how much water vapor is in the air to how much it can hold at that temperature . • It is always expressed as a percentage .

  3. Page 3
    Read page 3 as text

    Study Guide For example: • 100% relative humidity means the air is fully saturated . • Lower percentages mean the air is holding less moisture than it could. 1.7 Finding Relative Humidity There are two main ways to measure relative humidity. Method 1: Using a Hygrometer A hygrometer measures humidity using a simple but clever idea: • It uses a piece of hair attached to a pointer . • When humidity increases , the hair stretches , moving the pointer. • When humidity decreases , the hair shrinks , and the pointer moves back. This is why humid days are sometimes called “bad - hair days.” Method 2: Using Two Thermometers (Wet - Bulb and Dry - Bulb) Another method uses two thermometers and a chart , all based on the Celsius scale . If temperature readings come from a station model , they must be converted from Fahrenheit to Celsius . Station models show surface weather observations for a specific city. Here’s how the two thermometers work: • Dry - bulb thermometer o Measures the actual air temperature . • Wet - bulb thermometer o Has a wet wick wrapped around the bulb. o As water evaporates from the wick, it takes energy with it. o This causes the wet - bulb thermometer to cool down .

  4. Page 4
    Read page 4 as text

    Study Guide 1.8 Wet - Bulb Depression The difference between the dry - bulb and wet - bulb temperatures is called the wet - bulb depression . Important points to remember: • The wet - bulb temperature is always lower than or equal to the dry - bulb temperature. • If both temperatures are the same , the air is saturated , and the relative humidity is 100% . • Higher humidity → less evaporation → smaller temperature difference . • Lower humidity → more evaporation → larger temperature difference . The wet - bulb depression , along with the dry - bulb temperature, is used with a chart to find the relative humidity .

  5. Page 5
    Read page 5 as text

    Study Guide 1.9 Dew Point To measure moisture in the air using wet - bulb and dry - bulb thermometers, scientists use an instrument called a psychrometer . • A sling psychrometer is a handheld version that is spun in the air to get accurate readings. 1.10 What Is the Dew Point? The dew point is the temperature at which water vapor in the air changes into liquid water . • When air cools to its dew point, condensation begins. • If the dew point is below 0°C , it is called the frost point . Dew point and frost point are important because they help meteorologists decide when to issue frost and freeze warnings , which are especially important for agriculture and safety.

  6. Page 6
    Read page 6 as text

    Study Guide 1.11 Finding the Dew Point The dew - point temperature is found in a way similar to finding relative humidity: 1. Measure the dry - bulb temperature (air temperature). 2. Measure the wet - bulb temperature . 3. Find the wet - bulb depression (the difference between the two temperatures). 4. Use the dry - bulb temperature and the wet - bulb depression with a chart (like the one shown in the table) to determine the dew point . 1.12 Condensation and Fog Formation When water vapor comes into direct contact with a cooler surface , it can condense onto that surface. Fog forms when air cools to its dew point near the ground. There are different types of fog: • Advection fog o Forms when warm, moist air moves over a cold surface . o This cooling causes condensation and fog. o It can also happen when cooler air moves over a warmer surface . • Ground (radiation) fog o Forms at night due to radiational cooling . o Common in humid valleys and near rivers and lakes . 1.13 Clouds A cloud forms when air cools to its dew - point temperature higher in the atmosphere. • As air rises , it expands and cools. • Once it reaches the dew point, condensation begins and clouds form. • If the temperature is above 0°C , clouds are made of water droplets . • If the temperature is below 0°C , clouds contain ice crystals, snow crystals, and supercooled water .

  7. Page 7
    Read page 7 as text

    Study Guide 1.14 Types of Clouds Clouds are grouped into three main categories : • Cirrus clouds o Very high - altitude clouds o Made of ice crystals o Thin, wispy, and feathery in appearance • Stratus clouds o Low - level , layered clouds o Form sheet - like blankets across the sky • Cumulus clouds o Puffy , cotton - like clouds o Form from strong vertical rising of air Many clouds are combinations of these basic types. 1.15 Cloud Name Clues Cloud names often include prefixes or suffixes that give more information: • Alto means high altitude • Nimbus means the cloud is associated with rain or precipitation 1.16 Cloud Development Clouds form and grow because of how air moves, cools, and changes density . Let’s break this process down step by step.

  8. Page 8
    Read page 8 as text

    Study Guide 1.17 Rising Air and Cooling When a parcel of air rises , it begins to cool . This happens because: • Air pressure decreases with height . • As pressure drops, the air expands , and expanding air cools. The rate of cooling depends on how much moisture the air contains. 1.18 Adiabatic Lapse Rates • Dry air cools at a rate of 1°C for every 100 meters it rises. This is called the dry adiabatic lapse rate . • When the air contains moisture, the cooling rate slows to 0.6°C per 100 meters . This is known as the moist adiabatic lapse rate . The difference between these rates is caused by the high specific heat of water , which allows moist air to retain heat longer.

  9. Page 9
    Read page 9 as text

    Study Guide 1.19 Buoyancy and Vertical Cloud Growth When air near the surface is heated , it becomes: • Warmer than the surrounding air • Less dense • More buoyant , meaning it rises This buoyancy explains why clouds appear to float in the sky . As rising air continues to cool, clouds can grow vertically . In strong conditions, this process can lead to the formation of cumulonimbus clouds . • Cumulonimbus clouds are thunderstorm clouds • They are often associated with heavy rain, hail, strong winds, and tornadoes • These clouds form in an unstable air mass , where air movement is driven by density differences 1.20 Clouds in Stable Air Masses Not all clouds form from strong vertical motion. In a stable air mass , clouds can form when air is: • Forced upward by land features , such as mountains • Cooled by radiational cooling , especially when warm air mixes with a cooler layer These clouds are usually layered clouds , such as stratus clouds. 1.21 Cloud Base and Condensation Level Some clouds have a flat base and rise upward on top. • The base of the cloud forms where the air temperature equals the dew - point temperature . • This level is called the condensation level .

  10. Page 10
    Read page 10 as text

    Study Guide 1.22 Finding the Cloud Base Height The height of the cloud base, also called the lifting condensation level (LCL) , can be found in two ways. Method 1: Using a Formula 1. Find the difference between the air temperature and the dew point at the surface. 2. Divide that difference by 0.8°C (the rate at which dew point approaches air temperature per 100 meters). 3. Multiply the result by 100 to find the cloud base height in meters . Method 2: Using a Chart • Plot the air temperature along the solid lines . • Plot the dew - point temperature along the dashed lines . • Where the two lines meet, read across to the side labeled “Altitude.” • This value gives the cloud base height in kilometers . 1.23 Anvil - Shaped Cloud Tops As clouds continue to rise, they eventually reach a height where: • The cloud temperature equals the surrounding air temperature • The cloud is no longer buoyant At this point, the cloud spreads outward instead of upward, creating the flat, anvil - shaped tops commonly seen on large thunderstorm clouds. 1.24 Precipitation Precipitation includes all the ways water falls from the atmosphere to Earth, such as rain, snow, and hail. For precipitation to form, the atmosphere must meet two important conditions .

26 more pages in the full document

Unlock it once and it stays in your library, ready to chat with or turn into flashcards.

Unlock the full document

More Earth Science study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.