Category: clouds

What Exactly are Dust Devils?

Dusts Devils are a strange yet normal occurrence in the dry sandy deserts. Just mix up a day with rising temperatures and some wind and dirt devils spring to life.

Definition of Dust Devil

A small whirlwind containing sand or dust.

Description of Dust Devils

Dust Devils, sometimes called Dirt Devils, also known as whirlwinds or mini tornadoes, are relatively small, rotating columns of air that pick up dust or debris from the ground, making them visible. They are commonly seen in arid or desert areas, where the conditions for their formation are more favorable. Several factors contribute to the formation of dust devils:

Surface Heating: One of the primary factors that lead to the formation of dust devils is intense surface heating. In desert or arid regions, the sun’s energy can heat the ground quickly, creating temperature differences between the hot ground and the cooler air above.
Thermal Instability: As the ground heats up, the air in contact with it becomes warmer and less dense, causing it to rise. This rising warm air creates a localized area of low pressure at the surface, which in turn induces air from the surroundings to flow in and fill the void.
Wind Shear: Wind shear refers to a change in wind speed and direction with altitude. In areas where there is significant wind shear, the difference in wind speed and direction between the surface and higher altitudes can contribute to the rotation of the rising air column.
Surface Roughness: Uneven or rough terrain can also play a role in the formation of dust devils. Surface irregularities, such as rocks or vegetation, can create areas of differential heating and contribute to the generation of vortices.
Coriolis Effect: While the Coriolis effect is more significant in larger atmospheric systems, it can still have a minor influence on the rotation of dust devils. The Coriolis effect is caused by the Earth’s rotation and can impart a slight spin to the rising air column.

When these factors combine, a rising column of warm, low-pressure air can begin to rotate due to wind shear and other atmospheric dynamics. As the rotating column draws in dust and debris from the ground, it becomes visible as a dust devil. Dust devils are usually small in scale compared to tornadoes and are not typically as destructive, but they can still pose some hazards, especially if they encounter people or vehicles.

What Makes the Clouds?

CLOUD FORMATION

Clouds are visible masses of water vapor which are transformed into water droplets and ice crystals. Whether ice or water is formed is dependent upon the temperature of the air in the cloud, high clouds are in colder air than low clouds. The 3 key ingredients required for Earth’s cloud formation are Sun ( heat of infrared rays ), water ( oceans, lakes, plants ) and the atmosphere surrounding the planet. These 3 key ingredients are also required for life on our planet.

Requirements for clouds to form:

Evaporation: Water in oceans, lakes, plants etc are heated by sun rays or by wind blowing across the water surface vaporizing the water into the air

Convection: The process of vaporized water rising up into the atmosphere.

Condensation: The vapor grows colder and colder as it rises higher. The vaporized gets cold enough that the vapor turns back into liquid and attaches to dust particles in the air forming droplets. The droplets attach to each other and form clouds.

The Sun: The source of heat ( energy ) which effects all of our weather as temperature, cloud formation, pressure systems and wind.

Atmosphere: The mostly invisible blanket surrounding earth that keeps the heat in and excess radiation out.

CLOUD TYPES

The above cloud chart from jason.org show at what altitudes the different clouds appear.

Clouds are classified according to appearance ( visual texture ) and their height above ground level.

The following cloud roots and translations summarize the components of this classification system:

1) Cirro-: Curl of hair, high level.

2) Alto-: Mid level.

3) Strato-: Layer of cloud, low level.

4) Nimbo-: Rain, precipitation.

5) Cumulo-: Heaping.

CUMULUS Clouds are the most common clouds, the low-level white clouds look like puffy stacks of cotton balls. These are the clouds in which we can visualize rabbits, faces and alligators and what the imagination can render. They are are detached and individual. If cumulus clouds are present and are are not too tall the weather is typically nice. If conditions allow these can grow in height and size and can eventually form into cumulonimbus clouds which can indicate bad storms are likely. All cumulus clouds develop as a result of convection.

STRATUS Clouds are not puffy or billowing but are typically a gray color at the bottom which indicates water. They look like a continuous layer ( Strato ). They offer a gloomy overcast day and can provide light rain or drizzle, rain or snow.

CUMULONIMBUS low-level clouds grow on hot days when warm, wet air rises very high into the sky. From far away, they look like huge mountains or towers. If you watch and pay attention you can see the clouds change and keep on growing. These clouds can produce violent weather including heavy rain, hail and tornadoes.

High level clouds are Cirrus, Cirrostratus, and Cirrocumulus

High level clouds are far up in the sky, about 4 to 7 miles altitude, where temperatures are below freezing, so they are made of ice crystals.

CIRRUS Clouds looks like thin wispy curly locks of hair as shown in the image. Seeing these clouds in the sky usual tells us we will have fairly nice weather for a couple of days. Cirrus clouds indicate a change is coming.

CIRROSTRATUS Clouds are also high level but fill most of the sky and look like very-very thin batting in a blanket. They are commonly found in winter months and are ice crystals. The Sun or Moon above cirrostratus clouds give the appearance of having rings around them, which is caused by the light bouncing between the ice crystals. Cirrostratus clouds might indicate rain and/or snow can occur in the next day, although not very probable.

CIRROCUMULUS Clouds, also high level, are layered and have small clumps/lumps, see the image. These clouds can form what look like white color waves in the sky. Sunrise and sunset against cirrocumulus clouds can be quite impressive as the red and yellow light reflects along the bottom. Weather prediction: Fair, but cold.( the clouds are ice )

Mid level clouds are altostratus, altocumulus and Nimbostratus

Alto Mid level clouds are between high level cirrus clouds and low level stratos clouds. The mid level clouds altitude is generally 1.5 miles to 4 miles above the ground. Depending on temperature, altitude and time the clouds may consist of water vapor, ice crystals or both.

ALTOCUMULUS mid-level clouds are gray or alternating with white composed of ice crystals and water droplets. These clouds have a rippled appearance in which air is rising or falling amongst the ripples depending on the localized air temp and water content. Altocumulus clouds usually cover the entire sky. A weather prediction might be fair with these clouds present, although over the span of a day of transformation could lead to rain.

ALTOSTRATUS mid-level clouds are gray or blue-gray clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky. Weather prediction: Be prepared for continuous rain or snow!

NIMBOSTRATUS mid-level clouds are dark gray clouds that appear to dissolve into falling rain or snow. They are so thick that they often blot out the sunlight. Nimbostratus clouds provide gloomy days with rain or snow

Lenticular Clouds – UFOs

Lenticular clouds are shaped like glass lenses or ufos or Flying Saucers in the Clouds! They may get their shape from hilly terrain or just the way the air is rising over flat terrain. ¹

Sources:

https://www.SciJinks.gov

https://www.weather.gov/lmk/cloud_classification

https://weather-almanac.com/what-causes-wind/

What Exactly are Jet Streams?

A sketch of a couple of jet streams in northern and southern hemispheres

Jet Streams affect our winds down at the surface

As the jet streams move around the globe they rise and fall in altitude. The wind speeds high up in the mountains can be much stronger than in lower surrounding areas. This is due to the jet streams can be low enough to to be blowing through the mountain ranges. With dramatic changes in air pressure the jet streams altitude can change drastically. When wind speeds are above 50-mph the jet stream may only be a mile above the earth surface.

How many jet streams are there?

There are normally 4 jet streams traveling around the earth at the same time, 2 are in the southern hemisphere and 2 in the northern hemisphere. One of them is at latitude of approximately 60-degrees while the second is around the 30-degree latitude. The jet streams shift north or south with the changing seasons.

Why do the jet streams travel from west to east?

Because the Earth is rotating in that direction and surface tension is pulling the wind along in that general direction. The winds ave a tendency to want to move towards the cold poles of the globe.

How fast is the Earth rotating?

At the equator the earth rotates 1000 miles per hour based on 24,000 mile circumference and one rotation per day. On a perfectly still ( no wind ) day the air is also moving along at the same rate as the earth. At 45 degrees latitude, north or south, the earth is spinning in the 707 mph range ( because the distance at that latitude around the globe is shorter ).

How fast is the jet stream traveling?

The jet stream moves along at over 100 mph and even as high as 275 mph. For comparison, F-4 tornado wind speeds are 207 to 260 mph, F-5 are 261 to 318 mph. At the equator the jet stream is moving more slowly and picks up speed with the increase in latitude because as mentioned before, the distance around the globe is shorter, yet, the wind maintains it momentum and must travel faster to cover the same distance as at the equator. Wind speeds also increase with the increase of difference from low to high temperatures. The largest gradient between temperatures is at latitudes of 30-degrees and 60-degrees (north and south ) and therefore the wind speeds will be higher in these areas. Each of these ever changing factors contribute to the wind speed.

Jet Streams do not flow straight around the planet.

The jet streams stay in the boundaries between hot and cold air zones similar to a river staying within it’s banks. The shape of these air rivers is constantly changing as high pressure (cold) and low pressure (hot) cells are actively forming and collapsing. The jet streams general latitude changes as the seasons change, with winter having the strongest winds. The jet streams follow the sun’s latitude changes, ie as the sun moves south after the Summer Equinox, the jet streams will also. As earth enters summer the jet stream is moved farther towards the pole. In winter the jet stream moves closer to the equator.

In summary:

Jet streams are a constant phenomena whether we see them or not. They are constantly racing around the earth trying to find equilibrium between high and low pressure while the earth’s rotation is pulling them along from the west to the east. If the jet stream elevation is low enough we can have very strong winds, even up 100 mph. Jet streams top speed is around 275 mph, that’s in F-5 tornado wind speeds.