ATPL Meteorology - Class 7: Precipitation.

Summary

This meteorology lesson explores various types of precipitation, from drizzle to hail, and their formation due to rising air and temperature changes. Drizzle consists of small droplets under 0.5mm, while rain droplets exceed this size up to 5mm. Freezing drizzle and rain occur when temperatures are below zero but remain liquid. Snow, sleet, and hail are ice-based, with snowflakes varying greatly in size. Sleet is a mix of rain and snow, and hail forms in cumulonimbus clouds with strong updrafts. Precipitation intensity is categorized as slight, moderate, or heavy, based on the hourly rate of fall, with slight rain being under 0.5mm per hour and heavy exceeding 4mm per hour. Duration is described as continuous, intermittent, or in showers, aligning with cloud types and atmospheric conditions.

Takeaways

• 🌧️ Precipitation is any form of water or ice that falls from clouds to the Earth's surface, ranging from light drizzle to heavy hail.
• 💧 Drizzle is characterized by very small water droplets with a diameter of less than 0.5 millimeters.
• 🌦️ Rain consists of larger droplets, with diameters greater than 0.5 millimeters and up to 5 millimeters.
• ❄️ Snow can take various forms including snowflakes, snow grains, and snow pellets, each with different sizes.
• 🌨️ Sleet is a mix of rain and snow, or partially melted snow, and can vary in size and shape.
• ⛈️ Hail forms in strong updrafts within cumulonimbus clouds, where ice pellets rise and fall, colliding and accumulating layers of ice.
• 🌬️ The intensity of precipitation is measured by the amount that falls in an hour, with categories of slight, moderate, and heavy.
• ⏱️ The duration of precipitation can be continuous (over 60 minutes), intermittent (no clear breaks within an hour), or in the form of showers (on-off blocks of precipitation).
• 🌟 Cumuloform clouds, associated with unstable conditions and more rising air, are more likely to produce rain and hail.
• 🌫️ Stratiform clouds, with less rising air, are typically linked to drizzle and are associated with stable atmospheric conditions.
• ❄️ Freezing drizzle and freezing rain occur when droplets are supercooled below zero degrees Celsius but remain in liquid form until they encounter an impurity.

Q & A

What is precipitation and how does it form?

Precipitation is any form of water that falls from clouds back to the Earth's surface. It forms when rising air cools down to below the dew point, causing the air to become fully saturated and form clouds. The suspended water droplets or ice crystals then fall back to Earth as precipitation if they grow large and heavy enough for gravity to overcome the rising air.

What differentiates drizzle from rain in terms of droplet size?

Drizzle is characterized by small water droplets with a diameter of less than 0.5 millimeters. Rain, on the other hand, consists of larger droplets with a diameter larger than 0.5 millimeters but less than 5 millimeters.

How does the intensity of upward air motion affect the size of precipitation droplets?

The more intense the upward motion of the air, the larger the water droplets or ice crystals need to become to be pulled down to the Earth by gravity. This is because they must overcome the force of the rising air.

What types of clouds are associated with drizzle and rain?

Drizzle is more likely to be produced by stratiform clouds with less rising air, while rain generally comes from cumuloform clouds associated with unstable conditions and more rising air.

What is freezing drizzle and freezing rain, and how do they form?

Freezing drizzle and freezing rain occur when rain or drizzle droplets are supercooled to below zero degrees Celsius but remain in liquid form. This happens in very pure air with few impurities for ice crystals to form around. When these supercooled droplets encounter an impurity, they can rapidly freeze.

What are the different types of ice precipitation mentioned in the script?

The script mentions several types of ice precipitation: snow, which includes snowflakes, snow grains, and snow pellets; sleet, which is a combination of rain and snow; and hail, which forms in strong updrafts within cumulonimbus clouds.

How is hail formed and what conditions are necessary for its formation?

Hail forms when an ice pellet rises and falls within a cloud that has a lot of rising air, such as a cumulonimbus cloud. As the ice grows, it collides with more supercooled water droplets or ice particles, and the rising air sends it back up, repeating the process and gaining layers of ice. This requires very high levels of rising air and unstable conditions.

How is the intensity of precipitation measured?

The intensity of precipitation is measured in terms of slight, moderate, and heavy, which refers to the amount of precipitation that falls in an hour. Slight precipitation is less than 0.5 millimeters per hour, moderate is between 0.5 and 4 millimeters per hour, and heavy is anything more than 4 millimeters per hour.

What is the difference between continuous, intermittent, and shower types of precipitation?

Continuous precipitation lasts more than 60 minutes without a break. Intermittent precipitation occurs with no clear breaks within a 60-minute period but is not continuous throughout. Showers are on-off blocks of precipitation with clear gaps of no precipitation and periods of precipitation.

How are the terms 'slight,' 'moderate,' and 'heavy' defined for snowfall?

For snowfall, slight is defined as less than 0.5 centimeters per hour, moderate is between 0.5 and 4 centimeters per hour, and heavy is anything more than 4 centimeters per hour.