Question

geography

Q:1Several scientific studies have linked human-induced global warming to increased probabilities of extremely heavy precipitation events and/or to increased intensity of extremely heavy precipitation events in some parts of the world. What property of the atmosphere explains this connection between global warming and increased heavy precipitation?

Q2:Name two ways that an atmospheric inversion can form.

Q:3During which season is the mid-latitude storm track strongest (note it is the same answer for both hemispheres)? Why?

Q4:If cold and warm fronts mark boundaries between warmer and colder airmasses, what types of airmasses does an occluded front mark the boundary between?

Q:5If sea level pressure is higher in the Dalles than in Portland, what direction (north, south, east, or west) would you expect the winds in the Columbia River Gorge to be blowing from?

Q6Portland, OR gets less frequent severe weather compared with many other places. For example, severe heat waves, flash flooding, severe thunderstorms, extreme cold, and heavy snow are all relatively rare here compared with many other places. Please choose three of the above examples and explain why we don’t often experience the phenomenon

Severe weather describes a sub-type of weather that has particularly notable negative impacts on society. In some cases, whether or not a weather event is severe depends on the geography of where it occurs. Give an example of a weather event that would be considered severe in one place and not severe in another. Please indicate the geographic locations (i.e. Portland, OR) you are comparing. Also, please be climatologically accurate. For example, saying 3 feet of snow is severe in Portland but a normal occurrence in Boston would be incorrect. 3 feet of snow is a lot in any city! Feel free to use the internet to search whether your comparison fits climatology

Answer 1

1) Answer

The world is warming because humans are emitting heat-trapping greenhouse gases. We know this for certain; the science on this question is settled. Humans emit greenhouse gases, those gases should warm the planet, and we know the planet is warming. All of those statements are settled science.

Okay so what? Well, we would like to know what the implications are. Should we do something about it or not? How should we respond? How fast will changes occur? What are the costs of action compared to inaction? These are all areas of active research.

Part of answering these questions requires knowing how weather will change as the Earth warms. One weather phenomenon that directly affects humans is the pattern, amount, and intensity of rainfall and the availability of water. Water is essential wherever humans live, for agriculture, drinking, industry, etc. Too little water and drought increases risk of wild fires and can debilitate societies. Too much water and flooding can occur, washing away infrastructure and lives.

It’s a well-known scientific principle that warmer air holds more water vapor. In fact, the amount of moisture that can be held in air grows very rapidly as temperatures increase. So, it’s expected that in general, air will get moister as the Earth warms – provided there is a moisture source. This may cause more intense rainfalls and snow events, which lead to increased risk of flooding.

But warmer air can also more quickly evaporate water from surfaces. This means that areas where it’s not precipitating dry out more quickly. In fact, it’s likely that some regions will experience both more drought and more flooding in the future (just not at the same time!). The dry spells are longer and with faster evaporation causing dryness in soils. But, when the rains fall, they come in heavy downpours potentially leading to more floods. The recent flooding in California – which followed a very intense and prolonged drought – provides a great example.

Okay so what have we observed? It turns out our expectations were correct. Observations reveal more intense rainfalls and flooding in some areas. But in other regions there’s more evaporation and drying with increased drought. Some areas experience both.

Some questions remain. When temperatures get too high, there’s no continued increase in intense rain events. In fact, heavy precipitation events decrease at the highest temperatures. There are some clear reasons for this but for brevity, regardless of where measurements are made on Earth, there appears to be an increase of precipitation with temperature up until a peak and thereafter, more warming coincides with decreased precipitation.

A new clever study by Dr. Guiling Wang from the University of Connecticut and her colleagues has looked into this and they’ve made a surprising discovery. Their work was just published in Nature Climate Change. They report that the peak temperature (the temperature where maximum precipitation occurs) is not fixed in space or time. It is increasing in a warming world.

The idea is shown in the sketch below. Details vary with location but, as the world warms, there is a shift from one curve to the next, from left to right. The result is a shift such that more intense precipitation occurs at higher temperatures in future, while the drop-off moves to even higher temperatures.

  Traditionally, we have related precipitation events to the local average temperature. However, it’s clear that there’s a strong relationship between the peak temperature and the precipitation rates. In fact, relations reveal that precipitation rates are increasing between 5 and 10% for every degree C increase. The expected rate of increase, just based on thermodynamics is 7%.

The authors find that in some parts of the globe, the relationship is even stronger. For instance, in the tropics, there’s more than a 10% increase in precipitation for a degree Celsius increase in temperature. This is not unexpected because precipitation releases latent heat, which can in turn invigorate storms.

From a practical standpoint, this helps us plan for climate change (it is already occurring) including planning resiliency. In the United States, there has been a marked increase in the most intense rainfall events across the country. This has resulted in more severe flooding throughout the country.

In my state, we have had four 1000-year floods since the year 2000! Two years ago, Minneapolis, Minnesota had such flooding that people were literally fishing in the streets as lakes and streams overflowed and fish escaped the banks. No joke, I actually observed fish swimming past me as I waded up a street. This occurrence is being observed elsewhere in my country and around the world.

It falls upon city planners and engineers to design infrastructure that is more able to accommodate heavy rains and manage water. This means designing river containment areas or flood plains, reinforcing buildings and houses, and increasing the capacity of storm drainage in urban areas, just to name a few. These modifications present costs but not preparing for increased flooding poses even greater financial and social costs. Moreover, storing water from times when there is too much for the inevitable times when we have too little (drought), results in better water management and multiple benefits.

This shows why climate science is so important. The US government is in the process of decimating our climate science infrastructure. The current US congress and our president have lost the battle of science – they have no reputable scientists to hide behind in their climate change denial. But, what they are doing instead is decapitating our ability to predict and plan for the future. By defunding organizations like NASA, the EPA, and NOAA, they are making us fly blind into a future.

For comparison, the proposed increase in the Department of Defense budget would enable our military to buy more expensive weapons like the US Navy Joint Strike Fighter. At approximately $335 million per plane, giving up just six of those planes would be enough to maintain the climate budget of NASA.

I worked on the Joint Strike Fighter as a consultant. I understand the need to have a national military. But giving up our understanding of a changing climate for six jet fighters is actually decreasing our security, is, in plain English, dumb. It seems that our elected officials have a strange values system – a values system that will end up presenting us with much higher social and economic costs.

I hope we remember these values next time we have fish swimming in our streets or droughts shriveling our crops.

2) Answer

Inversions play an important role in determining cloud forms, precipitation, and visibility. An inversion acts as a cap on the upward movement of air from the layers below. As a result, convection produced by the heating of air from below is limited to levels below the inversion. Diffusion of dust, smoke, and other air pollutants is likewise limited. In regions where a pronounced low-level inversion is present, convective clouds cannot grow high enough to produce showers and, at the same time, visibility may be greatly reduced below the inversion, even in the absence of clouds, by the accumulation of dust and smoke particles. Because air near the base of an inversion tends to be cool, fog is frequently present there.

Inversions also affect diurnal variations in air temperature. The principal heating of air during the day is produced by its contact with a land surface that has been heated by the Sun’s radiation. Heat from the ground is communicated to the air by conduction and convection. Since an inversion will usually control the upper level to which heat is carried by convection, only a shallow layer of air will be heated if the inversion is low and large, and the rise in temperature will be great.

There are four kinds of inversions: ground, turbulence, subsidence, and frontal.

A ground inversion develops when air is cooled by contact with a colder surface until it becomes cooler than the overlying atmosphere; this occurs most often on clear nights, when the ground cools off rapidly by radiation. If the temperature of surface air drops below its dew point, fog may result. Topography greatly affects the magnitude of ground inversions. If the land is rolling or hilly, the cold air formed on the higher land surfaces tends to drain into the hollows, producing a larger and thicker inversion above low ground and little or none above higher elevations.

A turbulence inversion often forms when quiescent air overlies turbulent air. Within the turbulent layer, vertical mixing carries heat downward and cools the upper part of the layer. The unmixed air above is not cooled and eventually is warmer than the air below; an inversion then exists.

A subsidence inversion develops when a widespread layer of air descends. The layer is compressed and heated by the resulting increase in atmospheric pressure, and as a result the lapse rate of temperature is reduced. If the air mass sinks low enough, the air at higher altitudes becomes warmer than at lower altitudes, producing a temperature inversion. Subsidence inversions are common over the northern continents in winter and over the subtropical oceans; these regions generally have subsiding air because they are located under large high-pressure centres.

A frontal inversion occurs when a cold air mass undercuts a warm air mass and lifts it aloft; the front between the two air masses then has warm air above and cold air below. This kind of inversion has considerable slope, whereas other inversions are nearly horizontal. In addition, humidity may be high, and clouds may be present immediately above it.

3)Answer

In the mid-latitudes, synoptic storms bring moist air from the ocean to the land and in regions like Europe and North America they account for over 70% of total precipitation. Extreme rainfall is thus often associated with strong storm activity. Storm activity is also likely to affect temperature extremes. In summer – when near-surface temperatures are lower over oceans than over land – storms transport cool air from the oceans to continental regions. A decrease in summer storm activity could thus lead to the build-up of hot and dry conditions over the continents. During winter this effect might reverse as sea surface temperatures are higher than land temperatures. Storm activity is thus likely to have a moderating effect on continental temperatures and hence changes in storm tracks could affect not only precipitation and wind extremes but also heat waves and cold spells.

4) Anawer

Cold front

A cold front is located at the leading edge of the temperature drop off, which in an isotherm analysis shows up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts often bring heavy thunderstorms, rain, and hail. Cold fronts can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangle-shaped pips pointing in the direction of travel, and it is placed at the leading edge of the cooler air mass. Cold fronts come in association with a low-pressure area. The concept of colder, dense air "wedging" under the less dense warmer air is often used to depict how air is lifted along a frontal boundary. The cold air wedging underneath warmer air creates the strongest winds just above the ground surface, a phenomenon often associated with property-damaging wind gusts. This lift would then form a narrow line of showers and thunderstorms if enough moisture were present. However, this concept isn't an accurate description of the physical processes; upward motion is not produced because of warm air "ramping up" cold, dense air, rather, frontogenetical circulation is behind the upward forcing.

Warm front

Warm fronts are at the leading edge of a homogeneous warm air mass, which is located on the equatorward edge of the gradient in isotherms, and lie within broader troughs of low pressure than cold fronts. A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth's surface.

This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.

Occluded front

Occluded front depiction for the Northern Hemisphere

An occluded front is formed when a cold front overtakes a warm front, and usually forms around mature low-pressure areas. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point. It lies within a sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is warmer than the cold air ahead of the warm front and rides over the colder air mass while lifting the warm air.

A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Within the occlusion of the front, a circulation of air brings warm air upward and sends drafts of cold air downward, or vice versa depending on the occlusion the front is experiencing. Precipitations and clouds are associated with the trowal, the projection on the Earth's surface of the tongue of warm air aloft formed during the occlusion process of the depression.

Occluded fronts are indicated on a weather map by a purple line with alternating half-circles and triangles pointing in direction of travel. The trowal is indicated by a series of blue and red junction lines.

Stationary front

A stationary front is a non-moving (or stalled) boundary between two air masses, neither of which is strong enough to replace the other. They tend to remain essentially in the same area for extended periods of time, usually moving in waves.^[11] There is normally a broad temperature gradient behind the boundary with more widely spaced isotherm packing.

A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts either dissipate after several days or devolve into shear lines, but they can transform into a cold or warm front if conditions aloft change. Stationary fronts are marked on weather maps with alternating red half-circles and blue spikes pointing in opposite directions, indicating no significant movement.

When stationary fronts become smaller in scale, degenerating to a narrow zone where wind direction changes significantly over a relatively short distance, they become known as shearlines. A shearline is depicted as a line of red dots and dashes. Stationary fronts may bring snow or rain for a long period of time.

5) Answer

The Columbia River is the largest river in the Pacific Northwest region of North America.The river rises in the Rocky Mountains of British Columbia, Canada. It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean. The river is 1,243 miles (2,000 km) long, and its largest tributary is the Snake River. Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province. The fourth-largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific.

The Columbia and its tributaries have been central to the region's culture and economy for thousands of years. They have been used for transportation since ancient times, linking the region's many cultural groups. The river system hosts many species of anadromous fish, which migrate between freshwater habitats and the saline waters of the Pacific Ocean. These fish—especially the salmon species—provided the core subsistence for native peoples.

In the late 18th century, a private American ship became the first non-indigenous vessel to enter the river; it was followed by a British explorer, who navigated past the Oregon Coast Range into the Willamette Valley. In the following decades, fur trading companies used the Columbia as a key transportation route. Overland explorers entered the Willamette Valley through the scenic but treacherous Columbia River Gorge, and pioneers began to settle the valley in increasing numbers. Steamships along the river linked communities and facilitated trade; the arrival of railroads in the late 19th century, many running along the river, supplemented these links.

Since the late 19th century, public and private sectors have heavily developed the river. To aid ship and barge navigation, locks have been built along the lower Columbia and its tributaries, and dredging has opened, maintained, and enlarged shipping channels. Since the early 20th century, dams have been built across the river for power generation, navigation, irrigation, and flood control. The 14 hydroelectric dams on the Columbia's main stem and many more on its tributaries produce more than 44 percent of total US hydroelectric generation. Production of nuclear power has taken place at two sites along the river. Plutonium for nuclear weapons was produced for decades at the Hanford Site, which is now the most contaminated nuclear site in the US. These developments have greatly altered river environments in the watershed, mainly through industrial pollution and barriers to fish migration.

Columbia River

6) Answer

A heat wave, or heatwave,is a period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. While definitions vary, a heat wave is usually measured relative to the usual weather in the area and relative to normal temperatures for the season. Temperatures that people from a hotter climate consider normal can be called a heat wave in a cooler area if they are outside the normal climate pattern for that area.

The term is applied both to hot weather variations and to extraordinary spells of hot which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning. A heat wave is considered extreme weather that can be a natural disaster, and a danger because heat and sunlight may overheat the human body. Heat waves can usually be detected using forecasting instruments so that a warning call can be issued.

A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam, as occurred before the Johnstown Flood of 1889. Flash floods are distinguished from regular floods by having a timescale of fewer than six hours between rainfall and the onset of flooding. The water that is temporarily available is often used by plants with rapid germination and short growth cycles and by specially adapted animal life

Driving through a flash-flooded road

Flash floods can occur under several types of conditions. Flash flooding occurs when it rains rapidly on saturated soil or dry soil that has poor absorption ability. The runoff collects in gullies and streams and, as they join to form larger volumes, often form a fast flowing front of water and debris.

Flash floods most often occur in normally dry areas that have recently received precipitation, but they may be seen anywhere downstream from the source of the precipitation, even many miles from the source. In areas on or near volcanoes, flash floods have also occurred after eruptions, when glaciers have been melted by the intense heat. Flash floods are known to occur in the highest mountain ranges of the United States and are also common in the arid plains of the Southwestern United States. Flash flooding can also be caused by extensive rainfall released by hurricanes and other tropical storms, as well as the sudden thawing effect of ice dams. Human activities can also cause flash floods to occur. When dams fail, a large quantity of water can be released and destroy everything in its path

A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.

Thunderstorms result from the rapid upward movement of warm, moist air, sometimes along a front. As the warm, moist air moves upward, it cools, condenses, and forms a cumulonimbus cloud that can reach heights of over 20 kilometres (12 mi). As the rising air reaches its dew point temperature, water vapor condenses into water droplets or ice, reducing pressure locally within the thunderstorm cell. Any precipitation falls the long distance through the clouds towards the Earth's surface. As the droplets fall, they collide with other droplets and become larger. The falling droplets create a downdraft as it pulls cold air with it, and this cold air spreads out at the Earth's surface, occasionally causing strong winds that are commonly associated with thunderstorms.

Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes. Thunderstorms are responsible for the development and formation of many severe weather phenomena. Thunderstorms, and the phenomena that occur along with them, pose great hazards. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.

There are four types of thunderstorms: single-cell, multi-cell cluster, multi-cell lines and supercells. Supercell thunderstorms are the strongest and most severe. Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes. Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires from the heat generated from the cloud-to-ground lightning that accompanies them. Several means are used to study thunderstorms: weather radar, weather stations, and video photography. Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century. Beyond the Earth's atmosphere, thunderstorms have also been observed on the planets of Jupiter, Saturn, Neptune, and, probably, Venus.

A typical thunderstorm over a field

THE IMPACT OF WEATHER AND CLIMATE ON SOCIETY

There is widespread appreciation for the fact that the value of weather, climate, and environmental data, information, and forecasts is growing in importance to the U.S. economy (e.g., Colgan and Weiher, 2003). According to some estimates, up to 40 percent of the approximately $10 trillion U.S. economy is affected by weather and climate events annually (NRC, 1998a; NOAA, 2001b; Dutton, 2002). The cost of U.S. disasters related to weather and climate is rising rapidly, a consequence of population growth, rising wealth, and social behavior (Changnon, 2000; Pielke and Carbone, 2002). Approximately 90 percent of all presidentially declared disasters in the United States are weather-related (Kelly, 2001). Weather affects aviation, air quality, health, ground and marine transportation, defense, agriculture, fisheries, water, energy, construction, tourism, and many other sectors of the economy. Even “good” weather can cause problems in this complex society; for example, one unexpectedly warm winter day in the Northeast can cost utility companies millions of dollars a day in unused energy.

There is also a growing awareness of the impact of climate variability and change, on time scales ranging from months to decades (NRC, 2001a). Shifts in rainfall patterns associated with climatic variability, such as those accompanying El Niño and La Niña, result in a nation and a world that is often plagued by drought and floods at the same time. Demand for climate data, information, and forecasts is growing rapidly, with NOAA’s National Climate Data Center (NCDC) receiving nearly 2 million online contacts from users in the year 2000, 77 percent from industry.

As society becomes more sensitive to weather, the importance of weather prediction for the protection of lives and property and continued economic growth increases. For example, the U.S. population that resides within 50 miles of the nation’s coastlines and is most threatened by hurricanes and flooding is growing rapidly. Such population growth in these and other high-risk areas significantly increases the need for improved weather predictions and warnings to minimize risks to life and property. Another consideration is that the new economic concept of “just-in-time manufacturing” uses computer-timed and -directed supply systems to eliminate the warehousing of parts and products at ports and factories. However, even minor weather disruptions of land, sea, and air-supply-system pathways caused by snow, ice, and high-wind weather systems can now have large, leveraged impacts on these production systems, whereas previously they had little effect.