Climate: Environmental Geography - Assignment Example

Climate: Environmental Geography Q4. Why would climate change be a concern given this distribution of (fresh) water? Terrestrial life survives on freshwater. About 2% of the world’s water inventory is made up of fresh water. A major part (68.7%) of the global fresh water distribution is found in ice caps, glaciers, and permanent snow and about 30% in groundwater. Climate change leading to global warming could cause an intensification of the global hydrological cycle of rainfall, runoff and evaporation. Higher temperatures will cause ice caps and glaciers to melt earlier in the year, and lead to significant changes in river flow patterns such as less water during the warmer and drier summer months. The rivers are important for farming, manufacturing, drinking water supplies and as wildlife habitats. The changing water level patterns in the rivers will severely affect the supply of and demand for water. However, the effects on rivers will vary from region to region. Some regions may experience prolonged periods of drought while some others could experience excessive rainfall and flooding. The meltdown of ice caps and glaciers will increase river runoff leading to sea level rise. According to USGS, if all land ice melted the seas would rise about 70 meters (about 230 feet) (http://ga.water.usgs.gov/edu/waterdistribution.html). These effects of climate change are of concern. Q6. Describe the three states of matter as they apply to ice, water and water vapor. Water is unique because it can exist in gaseous, liquid, and solid phases within the relatively narrow range of temperatures and pressures found on earth which is mainly due to the shape of the water molecule. Whatever the phase, a water molecule consists of an atom of oxygen bound to two atoms of hydrogen. In its solid state as ice, the water molecules are present close together forming a crystal lattice connected by the hydrogen bonds. Ice crystals have a number of open regions and pockets in their structure making them less dense than liquid water and thereby causing the ice to float on water. The freezing point of water is 0°Celsius or 32°Fahrenheit. In the liquid state, the attractive forces between water molecules weaken and break free from the crystal structure. But the molecules are still attached to each other and the individual molecules attain greater mobility. This allows liquid water to assume the shape of its container. At its boiling point that is, at 100°C or 212°F, water forms water vapor which is the invisible, gaseous form of water. water vapor is the invisible gas. In this state, the hydrogen bonds binding the water molecules are broken and move freely. In other words, the average speed of molecular motion determines the phase of water. Water undergoes cyclic change of state within the atmosphere, oceans, and land at different regions and at various times through the processes of evaporation ( i.e., change from liquid to water vapor), condensation (from water vapor to liquid), and freezing (formation of ice and snow from water). This is known as the water (or hydrological) cycle. Q8. What is latent heat? How is it involved in the phase changes of water? Latent heat is the energy required to change a substance to a higher state of matter such as solid to liquid (e.g., ice to water), and liquid to gas (e.g., water to water vapor). The same amount of energy is released from the substance when the change of state is reversed. The latent heat involved in the formation of 1 gm of water from ice is 80 calories, and that involved in the conversion of 1 gm of liquid water to water vapor is 600 calories (Pidwirny, 2006). The same amount of heat energy is released when the process is in the reverse direction that is, 80 calories when 1 gm of liquid water freezes, and 600 calories when water vapor condenses forming 1 gm of liquid water. Q11. What is humidity? How is it related to the energy present in the atmosphere? To our personal comfort and how we perceive apparent temperatures? Humidity is the amount of water vapor contained in the air at any given time and place. The amount of water vapor in the atmosphere is dependent on evaporation and condensation. Humidity is linked to air temperature. The kinetic energy is higher in the warmer air. It is transferred to water molecules as the faster moving air molecules collide with the slower molecules in the water. The faster moving air molecules lose energy and the slower moving water molecules gain energy and begin to move faster and collide with each other more vigorously. Some of the water molecules will gain enough kinetic energy that enables them to overcome the attractive forces existing between the liquid molecules. Thus, a change of phase occurs from liquid to a free moving gas molecule. If the newly arriving air is colder the opposite occurs. Humidity, therefore, is a measure of how much of the energy available for evaporation has been used to free liquid water molecules from their neighbors. Environmental factors including airflow (wind), air temperature, humidity, and radiation from the sun and other heated surfaces determine human thermal comfort. Under hot conditions the body sheds heat to maintain thermal equilibrium. The evaporation of sweat from the skin is an important means of losing body heat. The efficiency of this cooling depends on the humidity; higher the humidity less effective is evaporative cooling, making one feel hotter. The human-perceived apparent temperature can be determined using the heat index (HI) data which combine air temperature and relative humidity. Q12. Define relative humidity. What does the concept represent? What is meant by the terms saturation and dew-point temperature? The amount of water vapor contained in the air at any given time is generally less than that required to saturate the air. Humidity is commonly expressed as relative humidity which is the amount of water in the air relative to the saturation amount the air can hold at a given temperature multiplied by 100. It is an indicator of the likelihood of precipitation, dew, or fog. Saturation is a condition in which a substance or gas will receive no more of another substance in solution or in a vapor. The dew-point temperature is the temperature at which the air cannot hold all of its water vapor, and some of the water vapor content condenses into liquid water. It is the temperature to which air must be cooled (at constant pressure and constant water vapor content) for saturation to occur. When the relative humidity is 100%, the dewpoint temperature and real temperature are the same, and clouds or fog can begin to form. Q15. How does the daily distribution of relative humidity compare with the daily distribution of temperature? The amount of water vapor the air can hold increases with temperature. Therefore, relative humidity decreases with increasing temperature provided the actual amount of water vapor remains constant. The daily distribution pattern of relative humidity shows a peak in the early hours of the morning (around 3 A.M.), reaching a minimum in the early afternoon (3 P.M.). In contrast, the daily temperature changes record a minimum in the early morning (3 A.M.), and a peak in the early afternoon (3 P.M.). Q16. Differentiate between stability and instability relative to a parcel of air rising vertically in the atmosphere? The stability or instability of an air mass depends on whether the isolated rising parcel of air is warmer or cooler than the surrounding air. The air is stable when it is cooler and, therefore, more dense and will sink. When air is stable, there is no convection. For example, stable air which is displaced up or down by mountains will return to its previous altitude. On the other hand, an unstable parcel of air is warmer, less dense and buoyancy forces will force it to rise further. Unstable air is associated with turbulent flow and convection. Q17. What are the forces acting on a vertically moving parcel of air? How are they affected by the density of the air parcel? The forces acting on a rising parcel of air are (1) adiabatic expansion due to which the air begins to cool, (2) When the temperature is lowered, the ability of the air to hold the water vapor decreases. After a certain elevation, the dew-point is reached which results in condensation and the formation of a cumulus cloud. Increases in the density of the air parcel will cause sinking of the parcel (as occurs in cool, stable air), while the opposite is true for decreases in density (e.g., warm, unstable air). Q18. How do adiabatic rates of heating and cooling in a vertically displaced air parcel differ from the normal lapse rate and environmental lapse rate? Adiabatic rates of heating and cooling in a vertically displaced air parcel occur due to the elevation or descent of the air parcel. Adiabatic lapse rate is the change in temperature of a mass of air as it moves upwards whereas the environmental lapse rate is change of temperature with altitude in the non-displaced air. Instability occurs due to differences in the adiabatic lapse rate of an air parcel and the environmental lapse rate in the atmosphere. If the adiabatic lapse rate is lower than the environmental lapse rate, air displaced upwards cools less rapidly than the surrounding air, and hence, will continue to rise. In contrast, if the adiabatic lapse rate is higher than the environmental lapse rate, the parcel of air moving vertically upwards cools more rapidly than the surrounding air. Hence, being cooler and, therefore, denser the air will tend to sink. Q19. Why is there a difference between the dry adiabatic rate (DAR) and moist adiabatic rate (MAR)? The rate of cooling of vertically rising moist air is lower than that of dry air; hence, MAR is usually lower than DAR. Q22. Specifically, what is a cloud? Describe the droplets that form a cloud. A cloud is condensed water or ice suspended in a mass of air. When water vapor in the air exceeds the saturation point as a result of air cooling because of rising, small cloud droplets begin to form. When adequate numbers of droplets of at least a few tenths of a micron form, they form a visible cloud. The droplets forming a cloud are water vapor condensed on particles (of dust, pollen etc.) termed condensation nuclei. The size range of the droplets can vary from 10 microns to 5 millimeters. The cloud droplets collide and coalesce to form a larger drop while some will grow as water condenses out the air directly onto the droplet. The water drops in the cloud may fall down to the earth as rain or snow, or may be transformed back into water vapor by evaporation. Q23. Explain the condensation process: What are the requirements? What two principle processes are discussed in the chapter? Condensation is the process by which water vapor is converted into water droplets forming a cloud in the sky or fog at the ground level. The requirements for condensation are (1) relative humidity should be very high (above 100%), (2) The presence of cloud condensation nuclei, i.e. tiny particles around which condensation can occur are required for cloud droplet formation. Condensation and coalescence are the two main processes characterizing the growth of droplets in a cloud. Q24. What are the basic forms of clouds? Using Table 7.2, describe how the basic cloud varies with altitude. The basic forms of clouds are: (1) Stratus or low clouds (found below 6000 feet), (2) Altostratus or middle clouds (6,000 – 20,000 feet), (3) Cirrus or high clouds (above 18,000 feet), and (4) Cumulus – Cumulonimbus (from 6,000-50,000 feet). Q25. Explain how clouds might be used as indicators of the conditions of the atmosphere and of expected weather. (1) Stratus clouds are uniform grayish clouds that often cover the entire sky, yielding usually no precipitation but just drizzle sometimes. Nimbostratus clouds form a dark gray cover, associated with continuous rain or snow. Altostratus clouds are grayish middle level clouds made up of ice crystals and water droplets, and covering the entire sky. Sun might be visible from behind the thinner areas of the cloud. Altostratus clouds are usually indicative of storms and continuous precipitation. (2) Altocumulus clouds are also middle level clouds that appear as gray, puffy masses, sometimes seen as parallel waves or bands. The presence of these clouds on a warm, humid summer morning could indicate thunderstorms to occur by late afternoon. (3) Cirrus clouds (High clouds) are thin, wispy clouds forming above 20,000 ft. These clouds usually move across the sky from west to east. They generally predict fair to pleasant weather. (4) Cumulus clouds are puffy clouds that resemble floating cotton. The base the cloud could be only 330 ft above the ground. These clouds grow upward, and they can develop into a giant cumulonimbus, which is a thunderstorm cloud. Q26. What type of cloud is fog? List and define the principal types of fog. The part of the stratus or low clouds that is in contact with higher ground could be considered as fog. 1. Radiation fog forms at night under clear skies with calm winds when heat absorbed by the earth’s surface during the day is radiated into space. It varies in depth from 3 feet to about 1,000 feet, and is stationary. Always found at ground level, it can greatly reduce visibility. Valley fog is a type of radiation fog. 2. Advection fog often looks like radiation fog, and is formed by condensation due to the horizontal movement of warm moist air over a cold surface. It moves horizontally along the ground. Sea fogs are advection fogs. 3. Upslope fog forms as light winds push moist air up a hillside or mountainside to a level where the air becomes saturated and condensation occurs. 4. Ice fog comprising of tiny ice crystals that are suspended in the air is formed when the air temperature goes below freezing. It is only encountered in cold Arctic / Polar air. 5. Evaporation or Mixing Fog arises when sufficient water vapor is added to the air by evaporation and the moist air mixes with cooler, relatively drier air. (National Weather Service, 2007). References National Weather Service, 2007. NOAA. Accessed on 5 July, 2010 from http://www.crh.noaa.gov/jkl/?n=fog_types Pidwirny, M. (2006). "Energy, Temperature, and Heat". Fundamentals of Physical Geography, 2nd Edition. Accessed on 5 July, 2010 from http://www.physicalgeography.net/fundamentals/6c.html Read More