In a world full of vibrant color, nothing quite vanquishes the atmospheric phenomenon that is the rainbow. Everyone has awaited the arrival of a rainbow once rainfall has ceased. Almost always, the ever reliable rainbow traverses across the sky emitting light in all wavelengths thus presenting its renowned look. But what does it take for these bows of color to form?
Rainbows are meteorological phenomenon that are caused by the reflection, refraction and dispersion of light in water droplets. This results in a spectrum of light appearing in a bow-like structure in the skies above. When observing a rainbow, one will notice that the outer part of the arc is red and the inner part is violet. This is caused by light being refracted when it enters a droplet of water, then reflected on the back side of the droplet and refracted again before leaving the water droplet. The rainbow effect occurs due to incoming light being reflected back over an angle range of 0 degrees and 42 degrees, with most intense light at 42 degrees. The reason the returning light is most intense at 42 degrees is because 42 degrees is known as the turning point—light hitting the outermost ring of the droplet and returning to the center at less than 42 degrees.
The amount of light that is being refracted is dependent on its wavelength, and hence its color. This is referred to as dispersion. Blue light, which has a shorter wavelength, is refracted at a greater angle than red light. But, due to the reflection of light rays from the back of the water droplet, blue light emerges from the droplet at a smaller angle. This causes blue light to appear on the inside of the rainbow arc and red on the outside of the rainbow arc.
Rainbows do not exist at one particular location either. In fact, many rainbows can exist, but only one can be observed depending on the observer’s viewpoint. All raindrops reflect and refract sunlight in similar ways, but only some light from raindrops reaches the observer’s eye. Rainbows appear to be curved due to the angle between the observer, the water droplet, and the sun. This angle perfectly creates the rainbow phenomenon between 40 and 42 degrees to the line between the observer’s head and their shadow.
Rainbows can be observed all around the globe and present a tranquil end to rainfall. Truly, rainbows are awe-inspiring enough that Pink Floyd depicted the dispersion effect on their The Dark Side of The Moon album. Everyone enjoys a rainbow that traverses across the sky and presents its dance of color, so be sure to look out and around when rain has ceased to fall to observe the atmosphere's true color.
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©2019 Weather Forecaster Alec Kownacki
Whether on the Great Lakes or on the coast of an ocean, everyone has felt a lake or sea breeze. A lake breeze is any wind that blows from a large body of water toward or onto a landmass. In the image above, it is displayed that low and high pressures play a key role in the development of these winds. With a lake or sea breeze, high pressure is lower near the surface of the water and low pressure is lower near the surface of the landmass. Wind prefers to travel from high to low pressure so this is where a lake or sea breeze comes from. Air temperature also plays a role in the formation of these winds. During the daytime when the landmass surface has undergone a few hours of solar heating, the air temperature on land rises above the air temperature over the water surface. This helps set up the high and low pressure system, thus creating the land or sea breeze phenomenon.
How do lake or sea breezes affect localized weather and what effects do these breezes have? A lake or sea breeze front is a weather front created by said lake or sea breeze. This front is also commonly known as a convergence zone. This front forms when the cold air from the water meets the warmer air from a landmass, which creates a boundary similar to a shallow cold front. With enough energy, this front can create cumulus clouds and become unstable if there is enough humidity, which can trigger thunderstorm development.
If there is already instability in the surrounding atmosphere, lake or sea breezes can be the factor needed to trigger thunderstorm development. Also, if a lake or sea breeze front collides with another frontal boundary, this too can trigger convection and thunderstorms development. This is commonly seen in the Florida panhandle. Sea breezes from the west coast of Florida and the east coast of Florida collide with one another near the middle of the landmass and cause thunderstorms to develop.
Next time you are on the beach and notice a rather strong breeze coming over the water, that very well could be a lake or sea breeze. Also, to confirm this, look inland and see if cumulus clouds are visible. This is a good indicator that a lake or sea breeze has initiated cloud development over land.
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©2019 Weather Forecaster Alec Kownacki
I recently was given the opportunity to conduct undergraduate research with a group of students from the University of Michigan, Virginia Tech, and University at Albany. We were headed to Greenland to conduct experiments on the atmospheric and geological conditions there.
This all started back in 1926 when professor William Hobb’s took the first atmospheric and geological experiments. He was a professor at University of Michigan, and since then there have been three other trips (including the one I was on) recreating the first one organized by William Hobb.. The most recent one was in 2006.
The 14 students from various universities geared up and all met in Albany NY. From there we did some classroom learning to get to know all the instruments we were going to be using. (If time allotted, you should definitely list out some of the instruments that you learned about!) It was really interesting working with students who had different majors and different skill sets. This allowed for many ways to solve a problem or a creative way in completing a task at hand.
Shortly after our Albany meet up, we loaded up in a C-130 and headed to Greenland. We were lucky to get to go at this time of year as they are in their summer. This means that there is 24 hours of sunlight. We had all the time in the world to go on hikes and conduct research because the sun never set!
We were all given these instruments and we told that this was our experiment, and we needed to figure out what we wanted to measure. A completely normal task that students have to figure out when conducting their own research, but we were undergraduates, and we had never done our own research. It was like letting a kid go loose in a candy shop – there were so many different things we could do!
We finally decided to do four different experiments.
The moral of this story, and the most important part, is that undergraduate research is so hard to come by. It opens doors for students and helps them discover more and more things about not only the weather but the climate, especially in regions that aren’t as explored – like Greenland. Being able to conduct this research at such a young age, made a lot of people on the team interested in going to graduate schoolor looking into research they can do on their own.
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@2019 Weather Forecaster Allison Finch
Many of us are aware of what a tropical cyclone (hurricane) is, but what about an extratropical one? Extratropical cyclones (aka mid-latitude cyclones) are those that we witness all year round here in the continental U.S. They are simply low pressure systems. Low pressure systems, unlike high pressure systems, rotate counterclockwise. This helps to create convergence since the air is converging towards the center and will want to rise. Thus, clouds and precipitation usually form, if other conditions are also right. These extratropical systems are frequently the cause of our precipitation, especially the stronger and heavier storms. This is because of the greater instability that is present, meaning the atmosphere has a lot of energy to work with. Typically, the stronger the system, the stronger the storm . For instance, many tornadic storms are the result of strong extratropical systems.
An extratropical cyclonegets its energy from the horizontal temperature contrasts that exist in the atmosphere. The temperature contrasts help to provide the forcing and instability needed for storm development in the form of frontal systems. These include cold fronts, warm fronts, and occluded fronts.On the other hand, tropical cyclonesare barotropic in nature, meaning there is constant pressure and density. This type of atmosphere results in no fronts and little temperature differences across the storm at the surface. Tropical cyclone winds are derived from the release of energy in the form of latent heat. Latent heat is energy which is transferred from one substance to another, such as evaporation and condensation processes. In the case of a tropical cyclone, it is due to cloud/rain formation from the warm moist air of the tropics. Furthermore, Tropical cyclones have their strongest winds near the surface of the Earth. In contrast, extratropical cyclones have their strongest winds near the tropopause, which is about 8 miles above the surface. These differences are due to the tropical cyclone being "warm-core" in the troposphere, whereas extra-tropical cyclones are "warm-core" in the stratosphere and "cold-core" in the troposphere. A “warm-core” system refers to a system which is warmer than its surroundings. A schematic view which shows the difference between “warm-core” cyclones (tropical) and “cold-core” cyclones (extratropical) are shown below.
As far as the similarities between the two, tropical cyclones and extratropical cyclones are both symmetrical. They also have surface areas of low pressure with winds that rotate counter clockwise. Furthermore, both produce very heavy precipitation and often times results in flooding. Both tropical cyclones and mid-latitude cyclones can last for several days, and sometimes as long as a week or more.
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@2019 Meteorologist Corey Clay
New research has found the record-breaking South American drought of 2013/14 with its succession of heatwaves and long-lasting marine heatwave had its origins in a climate event half a world away - over the Indian Ocean.
The findings published in Nature Geoscience by an international research team with authors from the Federal University of Santa Catarina in Brazil, Australia's ARC Centre of Excellence for Climate Extremes and NOAA in the U.S. suggest this may not have been the first time the Indian Ocean has brought extraordinary heat to the region.
It all started with strong atmospheric convection over the Indian Ocean that generated a powerful planetary wave that travelled across the South Pacific to the South Atlantic where it displaced the normal atmospheric circulation over South America. These atmospheric waves are similar to ocean swells generated by strong winds that travel thousands of kilometers from where they were generated. Large-scale atmospheric planetary waves form when the atmosphere is unstable, and this disturbance generates waves that travel around the planet.
"The atmospheric wave produced a large area of high pressure, known as a blocking high, that stalled off the east coast of Brazil," said lead author Dr Regina Rodrigues. "The impacts of the drought that followed were immense and prolonged, leading to a tripling of dengue fever cases, water shortages in São Paulo, and reduced coffee production that led to global shortages and worldwide price increases." That impact wasn't just felt on land as the high-pressure system stalled over the ocean. "Highs are associated with good weather. This means clear skies -- so more solar energy going into the ocean -- and low winds -- so less ocean cooling from evaporation. The result of this blocking high was an unprecedented marine heatwave that amplified the unusual atmospheric conditions and likely had an impact on local fisheries in the region."
The researchers found this atmospheric wave was not an isolated event and that strong convection far away in the Indian Ocean had previously led to drought impacts in South America. "Using observations from 1982 to 2016, we noticed an increase not only in frequency but also in duration, intensity and area of these marine heatwave events. For instance, on average these events have become 18 days longer, 0.05°C warmer and 7% larger per decade." said CLEX co-author Dr. Andrea Taschetto. The 2013/14 South American drought and marine heatwave is the latest climate case study to show how distant events in one region can have major climate impacts on the other side of the world.
"Researchers found that Australia's 2011 Ningaloo Nino in the Indian Ocean, which completely decimated coastal ecosystems and impacted fisheries, was caused by a La Niña event in the tropical Pacific," said Australian co-author Dr. Alex Sen Gupta. "Here we have yet another example of how interconnected our world is. Ultimately, our goal is to understand and use these complex remote connections to provide some forewarning of high impact extreme events around the world."
Regina R. Rodrigues, Andréa S. Taschetto, Alex Sen Gupta, Gregory R. Foltz. Common cause for severe droughts in South America and marine heatwaves in the South Atlantic. Nature Geoscience, 2019; DOI: 10.1038/s41561-019-0393-8
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© 2019 Oceanographer Daneeja Mawren
Pyrocumulonimbus cloud in Northern California in July 2014. Source: NASA Earth Observatory
From California to the Arctic, wildfires have been in the headlines for months now; their effects have been nothing short of far-reaching, as their smoky plumes have transported smoke to areas that are hundreds, if not thousands away from their sources. Such has been the case in Alaska, where significantly above-average temperatures have resulted in several uncontained wildfires. Their smoke plumes soon spread and et transported by atmospheric wind motions up into higher levels of the troposphere. In many instances, these conditions result in the development of a unique cloud type referred to as pyrocumulus clouds.
Wildfire in the Arctic Circle. Source: New York Post
These cloud types are essentially produced in much the same way that all other cloud types are; as the air around the wildfire heats up, its lighter density than the surrounding air allows for it to rise, bringing with it both the particles from the smoke and any water vapor that gets attached to said particles at the surface level. Once they condense, these particles and the water vapor that clung to them become what we refer to as a pyrocumulus cloud.
Pyrocumulus developing in Northern California. Sourvce: NASA Earth Observatory
As a wildfire continues to expand, so too does the area of greatest surface heating. As a result, those same vertical motions that helped to produce the initial pyrocumulus cloud will increase in intensity, resulting in more particles and water vapor making up and into higher levels of the troposphere. In some instances, these clouds can reach heights of up to 8 kilometers (5 miles), resulting in the development of pyrocumulonimbus clouds. Essentially, a wildfire of a strong enough size and magnitude can produce localized thunderstorms. Should these storms develop with low enough water vapor content, the end result can be virga and lightning strikes that can actually spark new fires in the surrounding areas. Likewise, if there is enough moisture content in the pyrcumulonimbus cloud, then the end-result can be rain that can kill off some, or all, of the wildfire that helped to produce it in the first place.
Wildfire in Shasta County, California on August 1st, 2014. Source: @Weather1225
In extremely rare instances, wildfires can even produce supercell thunderstorms! This was witnessed back in May 2018 over the Texas Panhandle when a substantially strong wildfire produced strong enough updrafts for a pyrocumulonimbus cloud to develop. This cloud just so happened to develop on a day with substantial low-level wind shear, low-level moisture, and instability supercell development. All that was needed was a source of lift, which in this instance came in the form of a wildfire. As a result, the cloud soon moved away from its source and evolved into a unique pyrosupercell just southeast of Amarillo, Texas.
Pyrosupercell thuderstorm just southeast of Amarillo, Texas, in May 2018. Source: Silver Lining Tours
Pyrocumulonimbus clouds are some of the most interesting cloud types out there; it can be said that these beasts are born out of the ashes, and as they evolve they can produce some of the most phenomenal and breathtaking sights on Earth. Indeed, these clouds are just one part of the dynamics and characteristics of a given wildfire, but their unique properties and evolution during such conditions are all worth the exploration.
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©2019 Meteorologist Gerardo Diaz Jr.
Discussion: The Hawaiian Islands are a special place that bring some of the most attractive weather year-round to its visitors and locals. Great weather, a season and location all coupled together create a rare phenomenon that only a few have ever seen, Lahaina Noon.
Lahaina Noon, a term coined by the Bernice Pauahi Bishop Museum in Honolulu, is so aptly named due to its native Hawaiian of la haina meaning “cruel sun”. With Hawaii being the only state in the US in the tropics, it experiences Lahaina Noon. This phenomenon is caused as the sun is directly overhead in a specific location or known as the sun’s zenith (subsolar polar point) travels to different locations across the earth, as the earth rotates and orbits the sun, when it hits that exact location of being overhead it creates an effect of no apparent shadow.
This rare occurrence remains often unheard of as it is limited to a specific area, this existing between the Tropic of Cancer and the Tropic of Capricorn (23.5°N and 23.5°S). This will allow for the event to occur twice per year. At the subsolar point the sun’s rays are perpendicular to the Earth’s surface. The angle between the location of the sun and an object is what casts a shadow, and when the angles are aligned (within these latitudes) the shadows appear mostly non-existent.
The next cities to experience Lahaina Noon in the United States are Hilo, on July 24th, at 12:27PM, Kailua-Kona on July 24th, 12:31PM and South Point, Hawai’i Island, July 28th, 12:29PM. For additional cities and more information on local Hawai’i astronomy in 2019 visit the Bernice Pauahi Bishop Museum.
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© 2019 Meteorologist Jessica Olsen
Almost always, clouds form in the troposphere, the lowest level of the atmosphere where we live and where all weather takes place. The troposphere easily has the most water vapor compared to any other layer of the atmosphere. In fact, the other layers have so little water vapor that it is incredibly difficult for clouds to form anywhere above the troposphere. However, on rare occasions, special mechanisms in the atmosphere can force water vapor to exist in above average quantities in the stratosphere or mesosphere.
The first of the two strange upper atmosphere clouds are called nacreous clouds, also known as mother-of-pearl clouds due to their vibrant colors. These clouds typically form in the polar regions of the stratosphere, the layer of the atmosphere just above the troposphere. Clouds are usually not found in the stratosphere because it is warmer there than at the top of the troposphere. The warmth of the stratosphere prevents air from rising past the troposphere due to convection, which is why clouds usually can’t form there. Nacreous clouds are the exception. Although the exact way they form is not completely understood, there are two major theories as to how they come about. The first method is by lingering updrafts of powerful storms. Storms have a section where they draw up moist, warm air called an updraft, and occasionally they can be so powerful that they drive water vapor into the lower stratosphere. If the temperature is cold enough in the lower stratosphere (about -85 degrees Celsius), spherical ice crystals can form and condense into nacreous clouds. The second method is through lifting from tall mountain chains. When air travels up tall mountain chains, sometimes water vapor from the lower atmosphere can find its way into the stratosphere via complex physical processes. Once again, if it is cold enough, nacreous clouds can form. Since the minimum temperature required for these clouds to form is so low, the only places one can see these clouds are near the poles. Further adding to the rarity of their sightings, the rainbow colors of nacreous clouds can only be seen when the sun is very low in the sky. Otherwise, nacreous clouds strongly resemble wispy cirrus clouds. An example of nacreous clouds at sunset is given below (photo credit: Albert de Nijs).
The second type of upper atmosphere clouds is called noctilucent clouds. These clouds form in the mesosphere, the layer right above the stratosphere. These clouds are known to be made of tiny ice particles, and are even thinner than nacreous clouds. Like nacreous clouds, they are still not completely understood. But, are plausible explanations as to how they get their water vapor. One explanation is that trapped water vapor in small meteors escapes into the mesosphere, where most meteors burn up. Another explanation is that the water vapor comes from chemical changes in methane over time. However these clouds form, one thing is certain: they are truly a sight to behold. These clouds are only seen right after the sun is over the horizon, when most of the sky is dark. The clouds glow as light from the sun strikes their ice particles from beyond the horizon. Sometimes, the clouds are so brilliant that they are mistaken for the aurora borealis. The only areas one can find these clouds are between the latitudes of about 50 to 65 degrees (north or south) during the summer when the mesosphere is coldest. The mesosphere must be quite cold for noctilucent clouds because they only form below -120 degrees Celsius. An example of one of these clouds is included in the thumbnail image of the article, while a diagram of atmospheric layers is included at the bottom (credit: NIWA).
These bizarre, scarce clouds are beautiful atmospheric phenomena that represent the complexity of the atmosphere. Complicated interactions in the upper atmosphere happen often, but it is rare for the average person to see such a clear product of them. Upper atmosphere clouds are truly fascinating formations that add to the allure of the sky.
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© 2019 Weather Forecaster Cole Bristow
Everyone is familiar with cloud-to-ground lightning which occurs during severe thunderstorms and cloud-to-cloud lightning which also is produced during these storms. In rare form, lightning can actually occur high above thunderstorms and give off a rather strange color and shape. These large-scale electrical discharges are called Sprites.
Sprites usually occur 50-90 km (31-56 mi) above cumulonimbus clouds. These cumulonimbus clouds, or simply just thunderstorm clouds, create enough electrical discharge for sprites to form above them. Sprites are usually triggered by the discharge of positive lightning between the underlying cumulonimbus and the ground. As can be seen in the image above, sprites are luminous reddish-orange flashes. They form within clusters above the troposphere, which is what gives them the jumbled or clustered appearance. Cloud-to-ground lightning along with our typical thunderstorms occur in the tropospheric region of the atmosphere. Sprites form within the stratospheric to mesospheric region of the atmosphere and this causes them to have different characteristics compared to lightning. Sprites are technically cold plasma phenomena that lack the hot channel temperatures found in tropospheric lightning. So, these sprites are more akin to fluorescent tube discharges than to lightning discharges. In a fluorescent tube, an electrical current excites a gas present and produces short-wave ultraviolet light which then causes, in the sprites case, light to be produced in the surrounding atmospheric area. As can be seen in the image above and other sprite images, the strands and strokes of sprites are caused by the electrical current. So, the glow of the sprite follows the current from the beginning to the end of its lifespan.
The image above helps visualize the height to which these sprites occur and the wide span of area that they take up. In this example, the sprite is spanning from 40 km to 80 km in the atmosphere. Surely, these electrical phenomena are not measly occurrences in terms of size. In terms of length of time, they are. Through optical imaging, a 10,000 frame-per-second high speed camera conveys that sprites are actually clusters of small, decameter-sized (10-100 m or 33-328 ft) balls of ionization. These are launched high into the atmosphere of about 80 km (50 mi) or so and then move downward at speeds of up to ten percent of the speed of light, which then are followed by separate sets of upward moving balls of ionization milliseconds later. Overall, an entire sprite display only lasts about the same duration of a cloud-to-ground lightning strike which is on average 30 microseconds.
Truly, to see an event like this one will need near-perfect atmospheric conditions along with a watchful eye.
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©2019 Weather Forecaster Alec Kownacki
For those having lived on the United States’ west coast from the era of about 2011-2017, especially those in California, drought was persistent, dangerous, and unprecedented in length and severity. As little came in the way of precipitation, especially the snow that fills the Sierra Nevadas and provides water for millions of Californians, reservoirs sank to record lows in capacity. Little water was available for anything more than necessity. Advisories were sent out to citizens advising and urging water saving strategies such as only watering lawns three times a week and only at night, replacing lawns with drought-tolerant landscaping, not serving water at restaurants unless upon request, installing water-efficient taps, showerheads, and more, and even cutting showers to no more than two minutes in duration. For California agriculture, the drought was arduous with smaller yields, and many farmers were forced to dig wells and tap into groundwater. Though, with all these results and effects, one may wonder: What was the precursor, the cause of the drought? The answer lies in something that climate scientist Dr. Daniel Swain coined: “The Ridiculously Resilient Ridge.”
The Ridiculously Resilient Ridge, or the RRR for short, is an atmospheric blocking phenomena appropriately named for its tenacity and unrelenting presence within the atmosphere off of California’s coast. A ridge is an area within the atmosphere in which there is unusually high pressure. In the case of the RRR, that pressure was ridiculously high. High enough to last for several years and cause the horrific drought conditions that Californians know all too well. But, how exactly does an area of high pressure bring about drought?
The key to answering this question is that areas of high pressure may act as a sort of physical wall to other systems that would otherwise try to move them and push them about. The stronger the wall is, or the higher the pressure is, the harder it is going to be to knock down that wall. As the ridge sat off the California coast, the jet stream and low pressure systems were forced up and above it, that of which brings necessary precipitation, leaving California with little to nothing in the way of water. Instead, California was met with nearly five years of dry, hot weather as the RRR prevailed and refused to subside. As each year went by with little to no precipitation, the effects of drought only compounded.
Come winter 2017, California had officially exited the drought after the RRR had finally weakened. With its downfall, atmospheric rivers of great strength were permitted to flow into California, These atmospheric rivers then brought some of the rainiest seasons on record after just having exited the most intense drought on record. Although California currently enjoys drought free years as a result of these intense atmospheric rivers, the RRR could very well rear its head again as global temperatures continue to warm. In California’s future, there certainly lies drought and lack of water. It simply is a matter of when conditions are right to birth Dr. Daniel Swain’s infamous Ridiculously Resilient Ridge.
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© 2019 Weather Forecaster Alexis Clouser