The boundary formed between the cold, subpolar, low pressure system and the warm, subtropical, high pressure system forms the polar front. Because the temperature differences between these polar and tropical air masses can be substantial, the polar front is quite dynamic. It can thus produce unstable and very changeable weather. The unsettled weather experienced by European countries in winter is often attributed moving low and high pressure zones as a result of moist air rising along the polar front. Similarly, the unseasonably cold weather in Eastern North America during the winter of 2014 partly resulted from the polar front extending south of the Great Lakes for an extended period of time. This was assisted by the polar jet stream and a strong polar vortex as we'll soon see. Jet streams form as concentrated zones of strong westerly winds in the upper and middle troposphere up to ten kilometers above the ground. Here the air from the poles and subtropics or air from the tropics and subtropics merge along cell boundaries. Jet streams influence weather patterns in the lower troposphere near the surface. Of these fast-moving ribbons of air, the polar jet stream coincides with the polar front. At about 8 to 10 kilometers altitude, migrating seasonally between 30 and 70 degrees latitude. When it is near the equator in the winter, it can move as fast as 300 kilometers per hour. The strength of the polar jet stream is enhanced by the dense polar air undercutting subtropical air. This leads to a very strong temperature gradient, which helps create storm systems, especially during winter. Storms carried by the jet stream often move rapidly across continents and cause intense precipitation. A similar, but usually weaker, subtropical jet stream occurs between 30 and 50 degrees latitude. In rare instances, the subtropical and polar jet streams can merge when the feral cell is weak. This can occur especially during winter. People flying in the mid-latitudes region will notice their flight durations affected by jet streams. How might this be? Select only one correct answer. A) longer flight times, both east to west, and west to east. B) shorter flight times, both east to west and west to east. C) longer flight times, east to west, but shorter times, west to east. D) Shorter flight times east to west, but longer times west to east. Since the mid latitude jet stream blows west to east, it will push planes going west to east, meaning they travel faster and arrive sooner. It will oppose those going east to west lengthening flight times. So only C is correct. As we have seen, evaporation is abundant at the equator but also occurs south of the polar front where the polar and ferrel cells rise. But it's not just water being evaporated. Other compounds often volatilized, which means they are converted to vapor and carried within rising moist air. Of particular concern is a category of organic compounds common in pesticides known as persistent organic pollutants, or POPs. These include the pesticide DDT, now banned in most of the world. These pollutants also include other compounds such as dioxin and PCB. Mercury and other heavy metal compounds are also a problem. Like liquid water, these compounds condense as air cools and rain out with precipitation. In tropical and temperate regions, POPs and heavy metals are often revolatilized when conditions are warm. But when they precipitate in polar regions these chemicals are there to stay as temperatures are seldom, if ever, warm enough to revolatilize them again and move them elsewhere. One hundred fifty years of industry and chemical production has made the arctic disproportionately polluted with POPs. Mercury and other compounds. Many of these compounds are soluble in fat and bio-accumulate within polar food webs. This means that they concentrate in species at the highest trophic levels. That is the apex predators in food webs. Which are those that are not predated upon by anything else. They accumulate these compounds abundantly from the animals that form their diet, and the plants and animals that form their prey's diets. Another effect of human activity in the Arctic atmosphere is the phenomenon of Arctic haze. Arctic haze is air pollution consisting primarily of sulfate aerosols and microscopic particulate matter. This material is carried to the arctic by winds from industrialized countries in the temperate northern hemisphere. Often seen as a reddish brown haze, it is particularly notable in the late winter and spring. This is when stable high pressure in the polar atmosphere allows haze to persist, without being removed by precipitation. Arctic haze was first noted by whalers and Inuit during the industrial revolution. Today, it is thought to result primarily from coal fired power plants in parts of Asia. Notably, there is no similar Antarctic haze in the Southern polar region. Given what we've learned about the accumulation of POP's and other detrimental compounds, Which pair of species below would be most negatively impacted? A) Polar Bears and Cod. B) Plankton and Narwhal. C) Polar Bears and Narwhal. D) Cod and Plankton. C is the correct answer. As an apex predator, polar bears are particularly affected by contaminants. This can be a particular concern where subsistence diets are rich in country food, especially that of marine mammals such as seal or narwhal. Sometimes food from these animals greatly exceeds it's recommended limits for these chemicals and may pose a risk to human health. This posses additional problems for subsidence cultures. Leading to potential over reliance on imported food and erosion of traditional culture and ways of life. The polar atmosphere has some unique features worth mentioning, you probably have seen a picture of the Northern Lights. This is the spectacle of colored lights dancing in the dark northern sky. This is the aurora borealis, caused by particles emitted from the sun called solar wind. The particles interact with Earth's magnetic field and collide with molecules and atoms in the upper atmosphere some 80 to 500 kilometers above the Earth's surface in both the northern and southern hemispheres. The phenomenon is named after the Roman goddess of dawn. Aurora. In Inuit mythology, the aurora is thought to be the light of torches carried by spirits to guide the dead to the sky portal of the heavens. In the arctic, it is referred to as aurora borealis after Boreas, the Greek god of North wind. In the Southern Hemisphere, it is called Aurora Australis. Astral, from the latin means South. Though the Northern Lights are most spectacular in the Arctic, they can also sometimes be observed farther south, depending on the activity of the sun. For example, in 2001 when solar activity was very high, the Aurora Borealis was visible as far south as California, Texas and even Jamaica. Another peculiar phenomenon of the polar atmosphere is that of sun dogs. These are bright spots to the left, right, and sometimes directly above the sun. The scientific name of the phenomenon is parhelia. Though they are sometimes called phantom suns. They're caused by the interaction of light with ice crystals in the atmosphere. Specifically by bending of light rays as they pass through the ice crystals. Sun dogs are one of many types of ice halos that can appear around the sun. No doubt many of you will have heard about how human activity has caused a hole in the Earth's ozone layer. But what is the ozone layer, and what's ozone anyway? About 90% of the ozone in the atmosphere occurs in the stratosphere. This is the layer of the atmosphere above the troposphere that sits 10 to 50 kilometers above the Earth's surface. The ozone concentration here is up to 0.3 parts per million, or 0.00003%. To put that number in context. About 21% of the air we breathe is breathable oxygen or O2. Ozone is itself a gas molecule made up of three oxygen atoms or O3. It is formed by the sun's ultraviolet or UV light. Interacting with ordinary, breathable oxygen O2. Breathable O2 is composed of only two oxygen atoms, high energy UV light breaks the chemical bond between oxygen atoms in O2, creating individual free oxygen atoms. When these free atoms interact with O2 molecules they form ozone. Ozone is itself unstable and is destroyed by ultraviolet light, producing a molecule of O2 and one free oxygen atom. Thus, the stratospheric o-zone layer, although a relatively minor component of the stratosphere, is naturally self-sustaining. This ozone layer is important, because it absorbs the high energy UV light from the sun that would otherwise be extremely damaging to life on Earth. The so called ozone hole in the stratosphere is actually two regions of relatively depleted ozone. One over each of the north and south poles. Various persistent chemicals produced by human activity, primarily synthetic chlorofluorocarbons, or CFCs are known to decompose ozone if they reach the stratosphere. They were formerly used in air conditioning systems. Refrigerators. And as propellants in aerosol sprays. CFCs do not break down by physical or biological processes. And therefore persist in the atmosphere. SFC's that make it into the stratosphere are broken own by ultraviolet light releasing free atoms of chlorine and fluorine. These free atoms, strip the third oxygen atoms from ozone, creating O2 In fact, a single chlorine atom can destroy as many as 100,000 ozone molecules over the 40 to 100 year residence time in the stratosphere. As O2 is transparent to ultraviolet light More dangerous UV rays will penetrate the ozone layer and reach earth's surface. These UV rays can damage living things, leading to sunburn, cataracts, and even cancer. You may recall we mentioned the polar vortex in terms of the cold North American winter of 2014. The polar vortex in each hemisphere is a persistent cyclone in the upper troposphere extending into the stratosphere and rotating around a central polar high pressure area. Driven by the temperature difference between cold polar air And warm sub tropical air polar vortices are strongest in the winter. It's winds can exceed those of the polar jet stream in strength. It is weaker in the summer. Air circulates counter clockwise in the arctic polar vortex. And clockwise in the Antarctic polar vortex. This is due to the Coriolis force in each hemisphere and is the same as all cyclones. The Arctic vortex has low pressure areas centered over Baffin Island in Canada, and in Siberia, giving it an elongate shape. When the arctic polar vortex is especially strong, and it's elongate pattern becomes essentially Meridional, strong winds can carry cold arctic air into otherwise temperate latitudes in North America or Europe. This took place in the winters of 2013, 2014, and 2014, 2015 even though the rest of the world was experiencing record heat such as in February 2015. Ozone depletion is most severe over Antarctica. But and ozone hole is also found over the Arctic. Which of the following atmospheric factors supports the development of these ozone holes over polar regions? Select all the answers you think are correct. A) strong and stable polar vortices. B) strong polar jet streams. C) stratospheric clouds in the stable polar vortices. D) a wavy Arctic and Antarctic polar vortex? A and C are correct. As we will now discuss. Ozone depletion is most severe over Antarctica. This is a result of the formation of the stratospheric clouds in the stable winter polar vortex, which act as catalysts for the breakdown of CFC's and the release of chlorine. As sunlight is absent for most of the polar winter there is no ultra violet light striking the atmosphere to replenish the depleted ozone. If the stable winter vortex is not disrupted the ozone hole grows throughout the polar winter reaching a maximum size during early spring. A similar ozone hole occurs over the Arctic during the polar winter but is normally less pronounced due to more variable atmospheric conditions. The largest Arctic ozone hole on record occurred during the Winter of 2011. When extremely cold winter temperatures and an unusually stable arctic polar vortex created conditions ideal for breaking down ozone. Recognizing the problem of ozone depletion. The international community gathered in Montreal in 1987 The result was the Montreal Protocol, an agreement phase out an then bam, the most dangerous CFC's. Despite this international effort, enough CFC's remain in the atmosphere to cause damage for 50 to 100 years or more. Enacted in 1989, the Montreal Protocol is a unique achievement as the first international treaty addressing a global environmental issue with the full ratification of all United Nation's members. The Montreal Protocol used the Precautionary Principle to limit and ultimately ban the use of chemicals thought to be dangerous on the basis of scientific predictions. It also included equal representation, when implemented by developed and developing countries. it is a success story for international cooperation on global issues. And has served as a model for subsequent efforts on global climate issues. However, the downside of the Montreal Protocol is that the successors to CFCs are hydrofluorocarbons or HFCs. Though much less dangerous to the ozone layer HFC's are potent greenhouse gases. Several thousand times more powerful than CO2 on a gram for gram basis.
