Meteorology p1 - humidity

Science Monkey

18 Jan 201410:42

Summary

TLDRThis video lesson introduces key concepts in meteorology, following a review of energy-related topics. It highlights extreme weather statistics in the U.S., such as the hottest and coldest recorded temperatures and the driest and wettest locations. The video then explains the difference between weather (short-term atmospheric conditions) and climate (long-term trends), with a focus on understanding humidity. Key terms like absolute and relative humidity, dew point, and how to use a sling psychrometer to measure them are introduced. The lesson ends with a brief look at how to calculate dew point and relative humidity using reference charts.

Takeaways

🌡️ Meteorology continues from energy topics, with many energy concepts applicable to weather.
🔥 Hottest temperature recorded: 134°F in Death Valley, California.
❄️ Coldest temperature recorded: -80°F in Prospect Creek, Alaska.
🌧️ Wettest location: Hawaii with 460 inches of rain in one month.
💨 Windiest location: Mount Washington, New Hampshire, with winds up to 231 mph.
⛅ Weather refers to short-term atmospheric conditions, while climate covers long-term conditions over years.
💧 Humidity refers to the moisture content in the air, with relative humidity being the percentage of water vapor saturation.
📈 As relative humidity increases, the chance of rain also increases due to higher water vapor content.
🧊 Dew point is the temperature at which air becomes fully saturated and can no longer hold water vapor, leading to precipitation.
🧪 A sling psychrometer is used to measure dew point and relative humidity by comparing the wet and dry bulb temperatures.

Q & A

What is the difference between weather and climate?
-Weather refers to the short-term conditions of the atmosphere, such as changes in temperature, moisture, air pressure, and wind, which can fluctuate from hour to hour or day to day. Climate, on the other hand, is the long-term pattern of weather conditions over several years or decades.
What are some extreme weather records in the United States?
-The hottest recorded temperature is 134°F in Death Valley, California. The coldest is -80°F in Prospect Creek, Alaska. The wettest location is Hawaii, which once received 460 inches of rain in one month. The snowiest location is in California with 390 inches of snow in a month, while Baghdad, California holds the record for the longest dry spell at 767 days without rain. The windiest location is Mount Washington, New Hampshire, with winds reaching 231 mph.
What is absolute humidity?
-Absolute humidity is the actual amount of water vapor in the air. For example, a parcel of air might have 10 grams of water vapor. However, this measurement is not commonly used because it doesn’t give a real sense of current weather conditions.
What is relative humidity, and why is it more useful than absolute humidity?
-Relative humidity is the percentage of saturation of the air, indicating how much water vapor the air is holding compared to the maximum it can hold. For instance, 50% relative humidity means the air is holding half of its capacity. It is more useful because it correlates with how comfortable or humid the air feels.
How is relative humidity related to the chance of rain?
-As relative humidity increases, the chance of precipitation also rises. For example, 90% relative humidity indicates a high chance of rain since the air is nearly saturated with moisture.
What is the dew point?
-The dew point is the temperature at which the air becomes fully saturated with water vapor, meaning it cannot hold any more moisture. If the air temperature drops to this point, condensation occurs, often leading to rain or dew formation.
How can the dew point temperature be measured?
-The dew point temperature can be measured using a sling psychrometer, which consists of a wet bulb and a dry bulb thermometer. By finding the difference in temperatures between the wet and dry bulbs, the dew point can be calculated using a reference chart.
How does a sling psychrometer work?
-A sling psychrometer has two thermometers: one with a wet bulb and one with a dry bulb. The wet bulb is moistened and both are swung around. The difference in temperatures between the two bulbs helps calculate relative humidity and dew point using a reference chart.
How do you calculate the dew point using a sling psychrometer?
-To calculate the dew point, subtract the wet bulb temperature from the dry bulb temperature. Find the dry bulb temperature on a reference chart, then find the temperature difference on the top of the chart. Where these values intersect gives the dew point.
How do you calculate relative humidity using a sling psychrometer?
-To calculate relative humidity, subtract the wet bulb temperature from the dry bulb temperature. Using a reference chart, find the dry bulb temperature on the left and the temperature difference on the top. The intersection of these two values gives the relative humidity.

Outlines

00:00

🌡️ Introduction to Meteorology and Extreme U.S. Weather Statistics

The speaker introduces the transition from studying energy to meteorology, explaining how concepts from energy will apply to the new unit. They provide interesting weather statistics from across the United States, including the hottest, coldest, wettest, snowiest, driest, and windiest locations. For example, Death Valley holds the highest recorded temperature (134°F), while Prospect Creek, Alaska, experienced -80°F. The weather extremes highlight the diversity of U.S. climate conditions.

05:03

🌦️ Difference Between Weather and Climate

The speaker explains the distinction between weather and climate. Weather refers to short-term atmospheric conditions, such as temperature, moisture, air pressure, and wind, which can change hour by hour or day by day. Climate, on the other hand, refers to long-term atmospheric patterns over years or decades. This section clarifies how weather reflects immediate changes, while climate provides an overarching trend.

10:04

💧 Humidity: Absolute vs. Relative

The speaker introduces humidity, defining it as the moisture content in the air. Absolute humidity is the specific amount of water vapor present in a block of air (e.g., 10 grams of water vapor). However, absolute humidity isn't widely used because it doesn't reflect actual weather conditions effectively. Instead, relative humidity is more useful, measuring the percentage of saturation in the air. For example, 50% relative humidity means the air is holding half the water vapor it can hold, while 100% means the air is fully saturated.

🌧️ Relative Humidity and Rain Prediction

Relative humidity is linked to the likelihood of rain. As the percentage of water vapor in the air increases, so does the chance of precipitation. The speaker uses examples like Chicago weather to demonstrate that higher relative humidity, such as 90%, correlates with a higher probability of rain. They also explain the dew point, which is the temperature at which air becomes fully saturated, leading to condensation and rainfall.

🌡️ The Dew Point and Measuring Tools

The dew point is the temperature at which the air is holding as much moisture as possible. When air cools to its dew point, it becomes saturated, and condensation occurs. The speaker introduces the sling psychrometer, a tool used to measure the dew point by comparing temperatures from a wet bulb and a dry bulb. By finding the difference between the two, it’s possible to determine the dew point and relative humidity using a reference chart.

📊 Calculating Dew Point and Relative Humidity

This section describes how to use the sling psychrometer and a reference table to calculate the dew point and relative humidity. The speaker walks through examples, such as determining the dew point with a dry bulb temperature of 12°C and a wet bulb temperature of 5°C. The same method applies to finding relative humidity, using dry bulb and wet bulb differences. The summary concludes by highlighting that these tools are essential for understanding humidity.

📈 Concluding Notes on Humidity and Air Pressure Preview

The speaker summarizes the key points covered so far, emphasizing the relationship between relative humidity, the dew point, and how to use a sling psychrometer to measure these variables. They briefly introduce the next topic, which will explore air pressure in the following lesson, and wrap up the screencast session.

Mindmap

Keywords

💡Weather

Weather refers to the short-term conditions of the atmosphere, including changes in temperature, moisture, air pressure, and wind. It can vary significantly from hour to hour, day to day, and season to season. In the script, weather is contrasted with climate and examples such as temperature fluctuations and rainfall in specific locations like Chicago are given to illustrate its variability.

💡Climate

Climate represents the long-term average of weather patterns in a specific area over extended periods, such as years or decades. It includes considerations of what the weather has been like over a significant time span. The script differentiates climate from weather by describing it as the 'long-term conditions' and emphasizes how it helps in understanding trends, unlike the more immediate and short-term concept of weather.

💡Humidity

Humidity is the amount of moisture or water vapor present in the air. The script explains two types: absolute humidity, which measures the exact amount of water vapor, and relative humidity, which compares the current moisture level to the maximum it could hold. The script uses examples like a 100-gram air parcel to illustrate how relative humidity is calculated and how it affects weather conditions such as the likelihood of rain.

💡Relative Humidity

Relative humidity is the percentage of water vapor in the air compared to the maximum it can hold at a given temperature. For example, 50% relative humidity means the air holds half the water it could potentially hold. The script highlights its role in predicting precipitation, with higher relative humidity indicating a greater chance of rain, as seen in the example of a 90% relative humidity correlating with a high likelihood of rain.

💡Dew Point

The dew point is the temperature at which air becomes fully saturated with moisture and cannot hold any more water vapor, resulting in condensation. The script explains that when air cools to its dew point, dew forms on surfaces like grass. It uses a scenario where a temperature drop causes air to reach its dew point, leading to rain, demonstrating its practical implications in weather prediction.

💡Sling Psychrometer

A sling psychrometer is a tool used to measure relative humidity and dew point by comparing the temperatures of a wet bulb and a dry bulb. The script describes its structure and function, including how it uses the difference in temperature readings between the two bulbs to determine moisture content in the air. This device helps calculate relative humidity and dew point using reference charts, which are critical for understanding atmospheric conditions.

💡Absolute Humidity

Absolute humidity measures the exact amount of water vapor present in a specific volume of air, expressed in grams of water vapor per cubic meter. The script mentions it as a less commonly used metric because it doesn't reflect the actual 'feel' of the weather conditions as well as relative humidity. An example from the script involves a 'parcel of air' with a specific amount of water vapor, illustrating how absolute humidity is quantified.

💡Air Parcel

An air parcel is a theoretical volume of air used in meteorology to analyze and model changes in air properties, such as temperature and moisture. In the script, it is used to explain humidity levels, with specific parcels being described as containing different amounts of water vapor, thereby showing how relative humidity changes as the water content in an air parcel changes.

💡Precipitation

Precipitation refers to any form of water—liquid or solid—that falls from the atmosphere and reaches the ground, including rain, snow, sleet, and hail. The script connects precipitation to relative humidity, explaining that higher relative humidity increases the likelihood of precipitation. This relationship is demonstrated through the example of high relative humidity leading to rain in a weather forecast.

💡Air Pressure

Air pressure is the force exerted by the weight of air molecules pressing down on the Earth’s surface. It influences weather patterns and can vary due to changes in temperature and altitude. Although the script does not delve deeply into air pressure, it sets up a segue for further discussion, indicating its importance in understanding atmospheric conditions alongside humidity and temperature.

Highlights

Introduction to meteorology after finishing energy-related concepts.

Weather statistics in the U.S., including hottest in Death Valley (134°F) and coldest in Alaska (−80°F).

Hawaii holds the record for wettest place with 460 inches of rain in one month.

Mount Washington, New Hampshire, holds the record for the highest wind speeds at 231 mph.

Definition of weather as short-term atmospheric conditions that can change from hour to hour or season to season.

Climate is defined as long-term atmospheric conditions over periods like two or ten years.

Introduction to humidity: the moisture content in the air, with a focus on absolute and relative humidity.

Relative humidity is explained as the percentage of air saturation with water vapor, where 100% means the air is fully saturated.

Relative humidity and precipitation: as relative humidity increases, the chance of rainfall also increases.

Introduction to dew point: the temperature at which air is fully saturated and can no longer hold moisture.

Explanation of how the dew point is related to weather phenomena, like dew forming on grass.

Introduction to the sling psychrometer, a device used to measure dew point and relative humidity by comparing wet and dry bulb temperatures.

Example of using a psychrometer to find dew point: subtracting the wet bulb from the dry bulb temperature.

Using the relative humidity and dew point chart with the sling psychrometer to determine weather conditions.

Closing remarks on understanding relative humidity, dew point, and the use of psychrometers in weather analysis.