Kids Corner
6th to 12th Grade
What causes wind?
Credit: Habby Hints
Wind is caused by differences in air pressure. When a cold air mass (which is more dense) is placed next to a warm air mass (which is less dense), the atmosphere creates wind to help equalize the difference in air pressure at various levels of the atmosphere over some given region. Winds will nearly always flow from areas of high pressure to areas of lower pressure; with some very rare exceptions.
Wind is caused by differences in air pressure. When a cold air mass (which is more dense) is placed next to a warm air mass (which is less dense), the atmosphere creates wind to help equalize the difference in air pressure at various levels of the atmosphere over some given region. Winds will nearly always flow from areas of high pressure to areas of lower pressure; with some very rare exceptions.
Source: NASA
What are the primary differences between types of more common atmospheric frontal boundaries?
A cold front is the somewhat straight boundary (i.e., which often has bends and curves based on the regional temperature and wind field) which often defines and/or represents the leading edge of a colder air mass. On a surface map, it is drawn with a blue line that has blue triangles facing the direction the air mass is headed. On the surface map below, one of the cold fronts extends from just above the Great Lakes and down south through a good portion of the state of Ohio. If you look closely at the temperatures, which are the numbers in red, you’ll notice the temperatures on the left side are cooler than the temperatures on the right side of the front. This is because cold fronts mark the leading edge of a colder air mass and with the passage of such a cold front, the cold air mass typically gets deeper with time in the context of a vertical profile of the lower/middle parts of the atmosphere. A cold front can also bring about differences in winds (changing speeds and directions) and weather conditions (e.g., frontal-enhanced and/or frontal-forced precipitation events).
Map credit: Habby Hints
What are winds like at different levels of the atmosphere?
If you look at a sounding (i.e., a vertical profile of the atmosphere which captures vertical profiles of temperature, dewpoint, wind speed, wind direction, etc), it can give you detailed information about winds on a vertical scale. Here are data from a sounding taken from Norman, OK at 12Z on Nov. 30th, 2017, drawn on a skew-t (i.e., a meteorological diagram which facilitates an effective way of visualizing the data from the vertical profiles of the atmospheric variables listed above): (note that Norman had calm, foggy weather at this time)
Image credit: NOAA Storm Prediction Center
On the left side of a skew-t, you will see at what pressure levels (in millibars (mb)) atmospheric data were measured at; on the right side you will find wind barbs at various elevation heights above the surface of the Earth at Norman, Oklahoma.
At the surface between 1000 and 850 mb, winds were generally calm, ranging from 5 to 20 knots and coming out of the north-northeast through that near-surface layer. Around 700 mb, we reach an inversion (i.e., a layer of the atmosphere in which there is a sudden increase in temperature for a brief time before the temperature profile again continues to decrease with height above a given layer), indicated by the sudden (and brief) increase in air temperature and an abrupt switch in the wind direction. From here, you see winds steadily increasing until they reach a maximum intensity of 90 knots at 200 mb, which is where we might find a jet streak. Above that height, winds begin to back off in intensity which is completely normal as you are approaching the tropopause which defines the boundary between the troposphere and the stratosphere. More specifically, the troposphere is the layer of the atmosphere in which most of the Earth’s weather phenomena occur. Then, the stratosphere is the layer just above the troposphere which is where air temperature stops decreasing with height and gradually begins to increase with height. It is worth noting that it is also at this height that the temperature stops decreasing with height and slowly begins to increase gradually with increasing height.
What is wind shear? What are veering winds?
Wind shear is a measure of the degree to which vertical wind speed and/or direction is changing with height. Wind shear is often referenced as a critical atmospheric wind parameter when assessing the potential for various types of severe, convective storms. Wind shear is also referenced as a proxy by which weather forecasters and research scientists evaluate hurricane activity based on the negative impacts imposed by vertical wind shear on developing, organized convection across large tropical oceanic basins. Veering winds are winds that change in a clockwise direction with increasing height. For example, if winds are southerly at the surface and gradually turn clockwise towards a westerly orientation by around 850 mb, these winds would be veering. Below is a sounding that exemplifies the process of vertically-veering winds occurring in real-life:
Source: National Weather Service
|
Directional Shear
"Wind direction changes with height"
"Directional wind shear is the change in wind direction with height. In the image below, the view is looking north. The wind near the surface is blowing from the southeast to the northwest." National Weather Service |
Speed Shear
"Wind speed changes with height."
"Speed shear is the change in wind speed with height. In the illustration below, the wind is increasing with height. This tends to create a rolling affect to the atmosphere and is believed to be a key component in the formation of mesocyclones which can lead to tornadoes." National Weather Service |
"The updraft lifts the rotating column of air created by the speed shear. This provides two different rotations to the supercell; cyclonic or counter clockwise rotation and an anti-cyclonic of clockwise rotation.
The directional shear amplifies the cyclonic rotation and diminishes the anti-cyclonic rotation (the rotation on the right side of the of the updraft)." National Weather Service
The directional shear amplifies the cyclonic rotation and diminishes the anti-cyclonic rotation (the rotation on the right side of the of the updraft)." National Weather Service
What is an atmospheric sounding and how is it used?
A sounding is a vertical profile of the atmosphere. It shows temperature data, wind data, and moisture data at different pressure levels of the atmosphere. These data can be used to calculate or extrapolate other data, such as inversion levels, boundaries, cloud levels, precipitation type, etc. Below is an example of a sounding on a skew-t. To learn more about the skew-t click the following link: http://www.weather.gov/source/zhu/ZHU_Training_Page/convective_parameters/skewt/skewtinfo.html
A sounding is a vertical profile of the atmosphere. It shows temperature data, wind data, and moisture data at different pressure levels of the atmosphere. These data can be used to calculate or extrapolate other data, such as inversion levels, boundaries, cloud levels, precipitation type, etc. Below is an example of a sounding on a skew-t. To learn more about the skew-t click the following link: http://www.weather.gov/source/zhu/ZHU_Training_Page/convective_parameters/skewt/skewtinfo.html
Why do cyclones spin in different directions in the Northern and Southern Hemisphere?
When looking at any form of satellite imagery depending on the time of the day, it is easy to recognize the fact that cyclones of any kind will always spin in opposite directions in the Northern and Southern Hemisphere, respectively. The reason for this different in cyclonic motion is a consequence of Coriolis Effect. On planet Earth, the Coriolis effect most often deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The Coriolis Effect occurs in such a way that a mass moving in a rotating system experiences a force which is perpendicular to the direction of motion. It is worth noting that the Coriolis Effect is also an important component involved in the formation of cyclonic weather systems.
What are the major ocean currents and how do they affect weather?
Ocean currents are effectively an energy transport system for oceanic basins all over the world. There are surface currents, which are driven by the atmosphere, and there are also thermohaline currents (i.e., deeper ocean currents which are primarily influenced by the constantly evolving changes in the ratio between fresh and saltwater), which are driven by variations in temperature and salinity and typically reside in much deeper sections of various oceans around the world. Ocean currents redirect the ocean’s heat while the Coriolis force pulls water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This process can also often generate features most commonly referred to as gyres.
A gyre is best defined as the flow of ocean water around the outer edges of an ocean basin and often, there is some degree of rotation of these ocean currents around one another to some extent. There are five major gyres in the world which include (but are certainly not limited to): the North Pacific, North Atlantic, South Atlantic, South Pacific and the Indian Ocean gyre.
Of all the ocean currents which exist, western currents like the Gulf Stream current are the deepest and the fastest. They move warm water towards the Polar regions and carry fewer nutrients than cooler currents that are found near certain coastlines often do. It is also worth noting that ocean currents do not generally flow in a straight path as denoted on idealized map renderings and parts of certain ocean currents can sometimes evolve into swirls, eddies, or other turbulent features. Eastern Hemisphere ocean currents carry cold waters to the equator and typically are broader as well as shallower than the ocean currents of the Western Hemisphere.
What causes lightning and thunder?
Around the world, there are literally thousands of thunderstorms which occur in different places on a near-routine basis. For nearly all thunderstorms, the fundamental reason for why they form is due to warm air rising and cooler air sinking and it is at the point at which the warm and cold air meet up that you will find moisture condensation, cloud formation, and ultimately, potential thunderstorm development. Within thunderstorms, you will mostly find ice crystals in the colder sections of the storm and water droplets in the warmer sections of the storm. It is when the ice crystals and the water droplets collide that you find the generation of static electrical charges in the cloud. Moreover, in nearly all cases you find the positively charged particles towards the top of the thunderstorm and then negatively charged particles towards the bottom of the thunderstorm as well as near and/or right at the surface of the Earth.
Much in the same way that a battery has a positively and a negatively charged side, there is a limit to the extent to which the magnitude of the positively and negatively charged sides can become before the situation becomes unstable in a battery. This is the same concept as that found in association with the positively and negatively charged particles distributions within thunderstorms anywhere on Earth. More specifically, when the oppositely charged particle clusters accumulate enough, the capacity of the air to sustain the particle charge differences collapses and there is a rapid discharge of electricity which is visually observed as lightning. The flash of lightning which is generated in association with a given thunderstorm temporarily equalizes (or stabilizes) the charged regions in the atmosphere until the opposite charges build up again which is when a flash of lightning will occur again. It is also worth noting that lightning strikes can occur between opposite charges within the thunderstorm cloud (which is referred to as intra-cloud lightning) or between opposite charges in the cloud and on the ground (which is referred to as cloud-to-ground lightning).
In short, thunder is caused by lightning indirectly due in part to the fact that lightning which can be as hot as around 50,000 °F often heats the surrounding air to as high as 18,000 °F. As a point of comparison, the average lightning strike temperature noted above is roughly five times hotter than the surface of the Sun which goes to show how hot lightning is. This intense heat associated with a given lightning strike causes the air surrounding the lightning strike to rapidly expand and induces a sound wave which is known as thunder. More specifically, the stepped leader causes the initial “tearing” sound, and the following ground streamer(s) or stroke(s) causes the sharp “crackling” sound which is often heard at a very close range.
Furthermore, it is also worth noting that thunder can sometimes be heard as far as 25 miles away from a given lightning discharge. At these distances, thunder will more often sound like a distant “light rumble” because the higher frequency pitches are more easily absorbed by the surrounding environment. Hence, the different sound waves set off by the source of the lightning discharge have different arrival times.
Much in the same way that a battery has a positively and a negatively charged side, there is a limit to the extent to which the magnitude of the positively and negatively charged sides can become before the situation becomes unstable in a battery. This is the same concept as that found in association with the positively and negatively charged particles distributions within thunderstorms anywhere on Earth. More specifically, when the oppositely charged particle clusters accumulate enough, the capacity of the air to sustain the particle charge differences collapses and there is a rapid discharge of electricity which is visually observed as lightning. The flash of lightning which is generated in association with a given thunderstorm temporarily equalizes (or stabilizes) the charged regions in the atmosphere until the opposite charges build up again which is when a flash of lightning will occur again. It is also worth noting that lightning strikes can occur between opposite charges within the thunderstorm cloud (which is referred to as intra-cloud lightning) or between opposite charges in the cloud and on the ground (which is referred to as cloud-to-ground lightning).
In short, thunder is caused by lightning indirectly due in part to the fact that lightning which can be as hot as around 50,000 °F often heats the surrounding air to as high as 18,000 °F. As a point of comparison, the average lightning strike temperature noted above is roughly five times hotter than the surface of the Sun which goes to show how hot lightning is. This intense heat associated with a given lightning strike causes the air surrounding the lightning strike to rapidly expand and induces a sound wave which is known as thunder. More specifically, the stepped leader causes the initial “tearing” sound, and the following ground streamer(s) or stroke(s) causes the sharp “crackling” sound which is often heard at a very close range.
Furthermore, it is also worth noting that thunder can sometimes be heard as far as 25 miles away from a given lightning discharge. At these distances, thunder will more often sound like a distant “light rumble” because the higher frequency pitches are more easily absorbed by the surrounding environment. Hence, the different sound waves set off by the source of the lightning discharge have different arrival times.
Idealized lightning schematic. Source: SciJinks
"Lightning observed by the GOES-16 Geostationary Lightning Mapper (GLM) illuminates the storms developing over southeast Texas on the morning of February 14, 2017.
Lightning is an important part of weather forecasting. The Geostationary Lightning Mapper instrument on the GOES-R series satellites can detect lightning activity over nearly the whole Western Hemisphere.
Scientists use data from GOES-R series satellites, along with data from the Lightning Imaging Sensor on NASA's Tropical Rainfall Measuring Mission satellite, to study lightning. This complete picture of lightning at any given time will improve "now-casting" of dangerous thunderstorms, tornadoes, hail, and flash floods." - SciJinks
Lightning is an important part of weather forecasting. The Geostationary Lightning Mapper instrument on the GOES-R series satellites can detect lightning activity over nearly the whole Western Hemisphere.
Scientists use data from GOES-R series satellites, along with data from the Lightning Imaging Sensor on NASA's Tropical Rainfall Measuring Mission satellite, to study lightning. This complete picture of lightning at any given time will improve "now-casting" of dangerous thunderstorms, tornadoes, hail, and flash floods." - SciJinks
What are the primary differences between a hurricane and a tornado?
First and foremost, a hurricane generally covers a MUCH larger region spatially (i.e., in terms of the square mileage a hurricane will typically cover from a cloud-cover perspective) than does a typical tornado. In addition, a hurricane typically affects weather on a synoptic (large) scale (i.e., a scale which is best defined as having weather phenomenon which occurs generally anywhere between 3 and 7 days), whereas a tornado is MUCH more localized in terms of its typical coverage zone. While both types of events can have profound, infamous, and memorable impacts on a given region, a hurricane develops over the course of days and/or weeks in most cases, whereas a tornado can be generated by a strong thunderstorm that may develop over the course of a matter of minutes or hours. Having said that, both types of events consistently have the ability to cause a tremendous amount of damage from both an economic and a logistical perspective on a region. However, hurricanes tend to affect coastal areas for the most part as opposed to tornadoes which tend to have the worst impacts on more inland regions of a given continent.
What are the stages of a maturing thunderstorm?
“Thunderstorms have three stages in their life cycle: The developing stage, the mature stage, and the dissipating stage. The developing stage of a thunderstorm is marked by a cumulus cloud which is the stage at which air is being pushed upward by a rising column of air (i.e., the thunderstorm’s primary updraft). The cumulus cloud soon looks like a tower (which is called towering cumulus) as the updraft continues to develop. There is little to no rain during this stage but occasional lightning. Thereafter, the thunderstorm enters the mature stage which is the stage at which the updraft continues to feed the storm, but precipitation begins to fall out of the storm, creating a downdraft (a column of air pushing downward). When the downdraft and rain-cooled air spreads out along the ground, it forms a gust front, or a line of gusty winds. The mature stage is the most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes. Eventually, a large amount of precipitation is produced and the updraft is overcome by the downdraft, which often marks the beginning of the dissipating stage. At the ground, the gust front moves out a long distance from the storm and cuts off the warm moist air that was feeding the thunderstorm. This typically marks the point of peak intensity for a given thunderstorm and when rainfall typically decreases in intensity, but lightning can often still remain to be a substantial danger.” NOAA National Severe Storms Laboratory
