Many people live near mountain chains, either on the windward side or the leeward side of the mountains. People who live on each side of the mountain can experience different weather phenomena because of a method called orographic lift.
Orographic lift is a term that defines what is happening when air rises over a land barrier, such as mountains or hills. Orographic lift is an adiabatic process, which means that all of the changes that happen within an air parcel occurs only in the parcel through changes in temperature and how much moisture can be condensed within the parcel. A parcel of air resembles a beach ball or a hot air balloon, but this is a theoretical construct where gases and particles within that parcel cannot escape it.
Air is less dense than land, so the air is forced to rise over land. As a result, the air starts to rise above the land barrier in question. As the parcel rises, the parcel cools down and condenses. The air will condense and start to form clouds when the temperature of the air equals that of the dew point. The height where the temperature and dew point are equal to each other is called the Lifted Condensation Level. People can see this when they see the base of the cloud. The air will not condense before this point and with mountain ranges, the clouds and precipitation fall on the windward side of the mountain. The windward side is the side of the mountain that the wind encounters. The land on the windward side of a mountain can be lush and green as a result of this precipitation.
On the other side of the mountain, the leeward side, the air rapidly descends and becomes warmer once more. The parcel now lacks some of the moisture that it contained on the windward side of the mountain because some of it precipitated out. As a result, the dewpoint and the temperature increased throughout its descent. The land on the leeward side of the mountain by forming an area called a ‘rain-shadow’ desert. As a rain-shadow desert implies, the land is dry due to the lack of precipitation and the higher temperatures on that side of the mountain.
So what does this mean for the people that live on each side of the mountain? Well, the climates of the windward and leeward side can vary due to the amount of precipitation in each place. This can be observed when examining the landscape of the windward and leeward side of a mountain chain. The windward side will have more vegetation because of the amount of precipitation that it receives, while the leeward side will lack that lush, green vegetation. Some rain shadow deserts can be defined as a desert-like climate as well.
This orographic lift can also be observed via satellites. Check out this Tweet from the National Weather Service in the Bay Area that depicts a rain shadow due to downsloping winds that occurred on February 26th!
The dark area in the middle of the satellite image is a ‘rain-shadow.’ The clouds are evaporating there because of the lack of moisture in that part of the region, but more clouds reform once more when it encounters the next land barrier. So even in the middle of a frontal system, orographic lift can still control which areas see precipitation.
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©2019 Weather Forecaster Shannon Sullivan
DISCUSSION: Every day in many places and regions spread around the world, there are substantial concerns tied to the ongoing threat of unpredictable landslide and/or mudslide events. Often, the biggest concerns are tied to the fact that when a given region experiences particularly heavy rainfall events over a relatively short period, there can often be a corresponding impact on both lower-level locations as well as more elevated locations in the form of a weakening of soil integrity.
More specifically, a substantially weakened soil integrity means that even with somewhat stabilizing features such as the roots of shrubs and/or trees, more saturated upper and middle soil layers can lead to there being a greater potential for landslides and/or mudslides under the corresponding and unfortunate circumstances. Moreover, when the right combination of circumstances comes into play and the threat of mudslides and landslides increases, this can lead to potential road closures, damage to local ecosystems, and even fatalities in some cases. Therefore, when there is a forecast for heavier rainfall in a region which is historically prone to landslides and/or mudslides because of heavier rainfall events, it is advisable for residents which are in the path of such threats to always heed the advice of emergency officials. In short, it is always better to get out of harms way than to try to figure out a clever way to get around such threats just by generating what is thought to be enough protection from such threats.
Moreover, depending on the type of soil composition in place within a given region, a given landslide or mudslide event can behave differently in terms of their total spatial extent and their impact reach from start to finish. Thus, in a world where rainfall events and precipitation totals in atmospheric events such as (but certainly not limited to) tropical cyclones are expected to likely become more extreme as time moves forward, there is a correspondingly increasing threat for the occurrence of such events and people should always take respective threats as serious as local officials and scientists are suggesting they may be under certain circumstances. The moral of this story is to always take geological threats such as landslides and mudslides as real as the threats always appear to be and never underestimate the power of falling rock and soil regardless of the exact steepness of a given slope.
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© 2019 Meteorologist Jordan Rabinowitz
Weather, Leaves, and Fall Foliage (credit: How Stuff Works, ThoughtCo, Durango Train, The Weather Channel, Smoky Mountains)
Image: Vibrant fall foliage - Credit ThoughtCo.
Discussion: Fall is here and that means it’s time to say goodbye to green leaves. Already, some areas in the Northern Hemisphere are seeing changes in leaf foliage. Temperature, sunlight, and soil moisture are key factors that determine the boldness and vibrancy of fall leaf colors. Spring and fall weather are key. Since leaves grow in the spring, wetter springs are ideal. In the fall, warm and sunny days paired with cool and dry nights yield colorful leaf foliage. Soil moisture in the spring and summer can help increase chances for a picturesque fall, though summer weather itself does not have a substantial impact on the fall foliage.
Image: Chlorophyll depicted in a leaf - Credit Smoky Mountains.
Chlorophyll is the plant molecule responsible for giving a leaf it’s green color. Leaves house other pigments as well,but chlorophyll masks them throughout most of the year. A shorter amount of daylight is the main cause for leaf color change. In the fall, when chlorophyll levels decrease, pigments of yellow by xanthophyll and orange by carotene are more visible. Photosynthesis is the process in which leaves interact with carbon dioxide and water to produce sugars and oxygen. When sugar is trapped in the leaf by the tree’s sealant, red and purple from anthocyanin pigment dominate. Cool nighttime air accompanied by daytime sunshine enhances red and purple colors.
Image: Fall foliage - Credit ThoughtCo.
Leaves will fall before fully developing color if the growing season is dry, there is early frost, heavy rain, or extreme wind eventsin the fall. Elevation and latitude also affect how early the leaves change. High elevations such as Denver, CO and/or higher latitudes such as Boston, MA will see earlier peak times and therefore falling of leaves.
Image: Fall 2018 foliage peak times - Credit The Weather Channel.
The Weather Channel recently explained the typical peak of fall foliage across the Continental U.S. Overall, the leaves change quicker in higher latitudes and elevations. In late September or early October, fall colors reach their peak in the highly elevated Rockies, as well as northern Minnesota, northern Wisconsin, norther Michigan, northern Pennsylvania, upstate New York, and northern New England in higher latitudes. Fall colors typically peak in the second half of October throughout the western region, Midwest into the South, and the majority of the Northeast. Sometimes the mid-Atlantic and Southeast coasts and parts of the Deep South are slow to peak. If that is the case this year, the leaves will peak in early November.
Image: Fallen leaves on the ground - Credit How Stuff Works.
Once this process is over, we usually forget about leaves until they bud again in the springtime. In actuality, leaves undergo a full cycle. After leaves fall, they decompose and create a rich humus, or dirt, on the ground that absorbs dew and rainfall. The fallen leaves are nutrient rich and act as sponges providing continual sources of nutrients and water to trees and other plants. In this way, leaves continually work as the life cycle ensures health and sustainability for trees until they sprout again the following spring.
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© 2018 Meteorologist Amber Liggett
DISCUSSION: Kilauea volcano on Hawai’i island is an active volcano with continuous eruptions dating to 1983. May 3rd, 2018 was the most current volcanic eruption cycle for Kilauea, opening fissures in Leilani Estates, Lanipuna Gardens, with an estimated 22 fissures having opened as recent as Monday, May 21st 2018 in Puna. To no surprise, due to this increase in volcanic activity this has brought about the influx of information given by the USGS (U.S. Geological Survey) to residents and new questions that prompt aid now from the NWS (National Weather Service).
According to the USGS, “Geology efforts address major societal issues that involve geologic hazards and disasters, climate variability and change, energy and mineral resources, ecosystem and human health, and ground-water availability.” With this, it is to be expected that the USGS and geologists alike are studying the impacts of the most recent fissures and eruption cycle of Kilauea. In addition to such work with monitoring the East Rift Zone activity, advance of lava flows, earthquake activity, such a localized volcanic event has also produced ashfall, gas emissions and are thus warning residents of potential hazards associated with Kilauea. However such hazards come with observational limitations that the USGS cannot resolve.
Queue the NWS and it’s team of meteorologists and atmospheric scientists.
The NWS states, “meteorology is the science concerned with the Earth’s atmosphere and it’s physical processes. A meteorologist is a physical scientist who observes, studies, or forecasts the weather.” While not entirely obvious as to why the NWS is needed during this current eruption, Geologists often observe the geologic feature (here being Kilauea), the hazard of this volcano, its transformation, significance, relation to seismic activity, and advancement of lava flows, however once the eruption reaches the troposphere, (the lowest layer of Earth’s atmosphere extending approximately 10 kilometers) the issue at hand becomes one for a meteorologist. The troposphere is the layer humans live in, with nearly all weather occurring in the troposphere. This is of interest as once a volcano such as Kilauea erupts, ashfall becomes a potential hazard for residents, including the increase of particulate matter into the atmosphere this brings concern for acidic rainfall, and redirection of flight patterns in and around the Hawaiian Islands as trade winds and the jet stream influence lower and upper level wind movement of the particulate matter.
This most recent volcanic activity has allowed for the coordination of geologists and meteorologists to provide residents in the East Rift zone with information on fissures, gas emissions, Vog (volcanic smog), lava inundation, ashfall propagation, and any advisories/watches/warnings associated with Kilauea.
For more information on Kilauea and other natural disasters developing, visit the Global Weather and Climate Center!
© 2018 Meteorologist Jessica Olsen
DISCUSSION: On May 3, the Island of Hawaii experienced the beginning of a major episode of the ongoing eruption of Mount Kilauea. Mount Kilauea has been actively erupting since January 3, 1983. Mount Kilauea is a shield volcano and generally erupts from the sides in small pockets called rift zones instead of straight through the top as one imagines a stereotypical volcanic eruption such as Mt. St. Helens. This latest episode is happening on the east rift zone of the volcano.
In recent days, this episode has increased ash production which is a danger to aircraft. Volcanic ash is a major problem for plane engines as the ash is known to damage the blades. In addition, the volcanic ash can contaminate the fuel which forces the engine to work harder increasing fuel consumption. In addition, the ash has reached up to 30,000 feet which would allow it to reach places such as central Mexico where it would worsen air quality. However, many of the major ash explosions have only reached an elevation of 10,000 feet. As a result, much of the ash is distributed over parts of the far east shore of the island of Hawaii and into the Pacific Ocean.
In addition to the ash, chemicals emitted from the volcano, most notably sulfur dioxide, has caused problems in the air quality for the Island of Hawaii. One of the problems with the sulfur dioxide is the creation of vog. Vog is a portmanteau of volcanic fog as it is formed from the interaction of water vapor with the volcanic emissions including sulfur dioxide. Another concern involved with the sulfur dioxide being emitted, is the formation of acid rain, which is very dangerous as acid rain can destroy trees and property. The concern of acid rain is mainly localized on the far east coast of the island of Hawaii and may even be a concern for the major city of Hilo if there is a wind shift to a southerly-southeasterly flow at low levels of the atmosphere. However, the west side of the island including Kona is not being affected as much as usual because the wind flow is the prevailing trade winds which come from the northeast.
The eruption has destroyed 37 buildings with only one injury reported. More damage is possible if many more fissures open in the rift. In addition, the emissions of sulfur oxides and methane will continue to be an air quality issue for a few weeks as it would take a while for the chemicals to clear up and be less concentrated.
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© 2018 Meteorologist JP Kalb
DISCUSSION: Ever since the Earth formed, many people around the world have continued to remain intrigued by how new islands form as the Earth has evolved. The key answer to this question often lies in certain places near the bottom of various oceanic basins around the world. At locations wherein there is an underwater volcano, such places are known as hot-spots. Hot-spots are effectively locations at which new land can form due to underwater volcanic eruptions ejecting volcanic material close to (if not right up to) the surface of the ocean above where the given eruption occurred. Thus, given the right sub- and surface-based oceanic conditions, new islands can form over the course of time.
It is worth noting the fact that underwater hot-spots were responsible for forming island chains around the world such as (but certainly not limited to) Hawaii. Thus, hot-spots provide a unique and viable method by which new islands and island chains can and do form in different parts of the world over very long periods of time. It is also important to note that such processes take a long time, so anyone interested in moving to a newer, developing island should not exactly "buy stock" in future building developments on these "growing islands" since it can often take centuries and even millennia until such islands are remotely ready to start being inhabited in any capacity. Thus, even though the premise of new islands forming in your lifetime may sound enticing, this does not always correlate to what you may think it will within a given lifetime.
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© 2018 Meteorologist Jordan Rabinowitz
If you have been keeping up with the Geosciences section, you may know that the last two months, the climate of the Triassic period and the Jurassic period were covered, in a mini-series designed to look at the climate of the different periods of the Mesozoic era. Now, a closer look at the last period in the Mesozoic era, the Cretaceous period (145 – 65 million years ago), will be reviewed.
The early Cretaceous was not much different than the late Jurassic. Sea levels continued to rise as continents continued to move, and tectonic plates continued to shift. As was happening in the Jurassic period, dinosaurs were evolving independent of one another, and becoming more and more specialized. One of these specialized predators includes the infamous Tyrannosaurus Rex.
Vegetation wise, the first of the angiosperms (flowering plants) started to grow. These plants started off small and weedy during the early Cretaceous, but by the late Cretaceous, large flowers had begun to form. These angiosperms had allowed a lot of grazing dinosaurs, like Triceratops, to flourish.
The end of the Cretaceous also saw a rise in today’s dominant life form: mammals. None of the mammals got any larger than a cat or small dog, most being mouse- or rat-size. Another evolution seen in the Cretaceous were small reptiles and amphibians, such as salamanders, turtles, or lizards.
It was also the end of the Cretaceous that changes in climate would start dramatically affecting future life on earth. Sea levels started to fall again, and temperatures started to lower. Volcanic activity was also occurring, causing a global cooling.
From here, the story is one we all know the ending to: A large asteroid collided with Earth, and more than half of the world’s animals, including the dinosaurs, went extinct. Despite this melancholy ending, the dinosaurs still remain some of the most fascinating creatures, and by looking at the climate of the Mesozoic era, a better understanding of them can be appreciated.
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© 2018 Weather Forecaster Joseph Fogarty
DISCUSSION: Last month, the climate of the Triassic period was explored. If you missed it, be sure to check it out here! This is now the second of three pieces to look at the climate of the Mesozoic era, where this month’s focus will be on the Jurassic period.
The Jurassic period occurred between 199 and 145 million years ago. Dinosaurs had begun to evolve and thrive during the Triassic period, but the large increase in dinosaur diversity, as well as the presence of new plesiosaurs (marine reptiles) and pterosaurs (flying reptiles), began to manifest itself during the Jurassic period.
In the early Jurassic, animals were still similar throughout the world due to the connected nature of the continents – however, these continents slowly started to drift apart, allowing for a greater diversity of dinosaurs in the mid to late Jurassic. As continents drifted apart, more land masses and coastlines were created, allowing oceans to widen and sea levels to increase. Epicontinental seas (also known as inland seas) started to form due to these rising sea levels. These rising sea levels caused an increase in the humidity level, which marks a big difference between the Triassic and the Jurassic. While the Triassic climate was dry, the Jurassic climate was wetter and more humid, and almost resembled a rainforest in the tropical areas.
These rainforest-like conditions paved the way for lush vegetation to grow, slightly increasing the carbon dioxide levels, therefore creating a “greenhouse” climate and warming throughout the world. Vegetation in the Jurassic period included a more diverse set of plants, catering to all of the different types of specialized dinosaurs that had started to evolve during this time. Some examples of these specialized dinosaurs include tetanurans (both large and small carnivores), thyreophorans (armored herbivores, such as stegosaurus and ankylosaurs), and sauropods (large herbivores, such as Brachiosaurus and Diplodocus).
The many different types of plants that appeared in the Jurassic provided resources for all the different types of herbivores. The long-necked sauropods could spend their time devouring tall conifers, and the ground-level head of the stegosaurs and ankylosaurs could graze on the low-lying plants, such as ferns and horsetails.
One of the most diverse dinosaur fossil deposition on earth, the Morrison Formation, was created during this time. The Rocky Mountains began to uplift during the Jurassic period, and as they weathered, sands became deposited at the sides of the mountain into lakes, swamps, and streams. In the early twentieth century, this was the place to be to find fossils!
Stay tuned for next month, where the Cretaceous period is covered in the last of three pieces on the climate of the dinosaurs. If you want to read more storeis like this, and learn more about the geosciences, be sure to visit here!
© 2018 Weather Forecaster Joseph Fogarty
DISCUSSION: Studying dinosaurs was a highlight for many young elementary school students in science class. Triceratops, Stegosaurus, and the notorious Tyrannosaurus Rex are all fascinating creatures that nearly everyone remembers. However, the climate of the different periods of the Mesozoic era (Triassic, Jurassic, and Cretaceous) is not something everyone remembers. Yet it is important to study, as the climate of any particular period determined which types of animals thrived while others struggled for survival. This is the first of three pieces that intend to look at the climate and its relation to dinosaurs in the three periods of the Mesozoic Era.
The Triassic period, which occurred between 251 million and 199 million years ago, marked the first appearance of the dinosaurs. The Permian-Triassic extinction event, which happened 251 million years ago, is the largest known extinction event; a total of about 95% of all life went extinct. This event marked the boundary of the Permian and Triassic period, also known as the P-T boundary. Since almost all species became extinct, there was a very low biodiversity at the start of the Triassic.
A possible cause of the P-T extinction is the massive eruptive event of the Siberian lava traps, a large region of volcanic rock in Siberia, Russia. As these volcanoes erupted, the Earth underwent a global warming due to the massive CO2 emission. This warming created an uninhabitable atmosphere, which made the land mostly barren for the 5% of organisms that survived the extinction event. Another consequence of these eruptive events was oceans becoming an anoxic environment, i.e. they had little to no dissolved oxygen. This made marine life inhabitable as well at the end of the Permian period.
The geography of the Triassic period was a major factor in shaping the climate. The supercontinent Pangea started to take shape, with all continents together as one. The fact that all land was attached, combined with the low biodiversity of animals post-extinction, meant life was similar everywhere on Earth. The climate of Pangea was very hot and dry, especially in the interior. This may explain why reptiles and dinosaurs became dominant, and not mammals. Near coastal regions, a seasonal monsoon climate prevailed as well. The land was barren of plant life, but certain plants did survive the P-T extinction. These plants included ferns, woody plants, and gymnosperms (a plant with cones or pollen spores).
The surviving groups of animals that survived the P-T extinction were therapsids, who were mammal-like reptiles, and archosaurs, a more reptile-like organism. The archosaurs had evolved into dinosaurs by the mid-Triassic, and therapsids had almost gone extinct, meaning that the hot and dry climate was better suited to these reptilian-like animals. Many of these reptiles evolved into sprawlers, and some evolved into bipedal creatures (creatures who walked on two legs), such as Coelophysis (below). Towards the end of the Triassic, another group had evolved from the surviving archosaurs, called the pterosaurs (a term for winged reptiles).
Stay tuned for next month, where the climate and dinosaurs of the Jurassic period is covered. If you want to learn more about the geosciences, be sure to visit here!
© 2018 Weather Forecaster Joseph Fogarty
DISCUSSION: Have you ever taken a vacation to a city and then drove by a rural area for a pit stop? Have you stopped and thought, “man it sure is cooler here than in the city?”
There’s a name for this feeling. It’s called the Urban Heat Island. In simpler terms, it says that cities are 1-5°C warmer than rural areas. The effects of this phenomenon can go beyond city limits. These are the reasons for the Urban Heat Island: reduction in evapotranspiration, composition of materials in the city, pollution, and excess heat from human (anthropogenic) activity.
By definition, evapotranspiration is when water gets transferred to the atmosphere by evaporation from the land and transpiration from plants. Unless there is a garden or park within city limits, there is reduced vegetation in the city. Therefore, this allows for more sensible heat and warmer temperatures. In addition to this, areas where water can’t be absorbed within the city promote runoff.
Urban areas have lower albedos, which means less reflection and more absorption of sunlight. The construction materials have high heat capacities and thermal conductivity. These are defined, respectfully as, the ability to raise a degree of an object by 1 degree Celsius, and the ability to conduct heat. Energy is stored in the day and released at night.
Pollution can act like a shield over the city. What is meant by this “shield of pollution” is that this “shield” can act as a barrier against outgoing longwave radiation from leaving. Once this radiation attempts to leave, the “shield” will just send it right back to the city. This explains the increase in nocturnal temperature in cities.
The following things humans do can release heat: transportation, cooling apparatuses such as air conditioners, street lights, etc.
In conclusion, the effects of urbanization can have an immediate effect on the weather.
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“©2017 Weather Forecaster Jennifer Naillon