" max. T = 2.898#10 $3 metres Kelvin

Transcription

1 Question 1 The Earth s climate and weather is driven by energy coming from the Sun. The temperature of the Earth is determined by a balance between incoming radiation from the Sun and that radiated back out to space from the Earth. (a) Briefly describe the difference between the spectrum of radiation from the Earth and that from the Sun, with reference to a blackbody spectrum. (2 marks). Both the sun and earth has a (close to) blackbody spectrum but the spectrum of the earth peaks at a longer wavelength in the infrared while the spectrum of radiation from the sun peaks in the visible. This is due to the different temperatures (around 290 Kelvin for the earth, and 6000 Kelvin for the sun. Give one mark for statement that the two blackbody spectra peak at different wavelengths (with the earth being at longer wavelengths); a half mark for a statement of the approximate wavelength region of each; and a half mark for mention of the approximate temperature for each situation. (b) Because of its atmosphere, the Earth has an equilibrium temperature that is warmer than that expected in the absence of an atmosphere (this is the natural greenhouse effect). Draw a diagram showing the flow of energy into, through, and out of the Earth s atmosphere. Highlight the areas that give rise to the greenhouse effect. (3 marks)

2 Key features to show in diagram are: radiation from the sun; absorbed by the earth and re-radiated. Much of this re-radiated energy is absorbed by the atmosphere before either being radiated to space or back to the ground. It is this component that gives rise to the greenhouse effect. Note that the diagram above only shows radiation absorbed by the earth. There is also radiation reflected by clouds and the surface of the earth. Give one mark for radiation from the sun being absorbed by the earth; one mark for the earth radiating back outwards; and one mark for this radiation being absorbed by the earth s atmosphere producing the greenhouse effect. (c) Wien s Displacement Law " max T = 2.898#10 $3 metres Kelvin relates the wavelength " max of the peak of a blackbody spectrum and the temperature T of the blackbody. Calculate the peak wavelength in nanometres (1 nanometre is 10 "9 metres) for: (i) a blackbody of temperature 6000 K; (ii) a blackbody of temperature 300 K. (3 marks) (i) (ii) 483 nm (1.5 marks) 9660 nm (1.5 marks) (d) Name two things in the Earth s atmosphere or on the surface that tend to decrease the equilibrium temperature of the Earth. (2 marks) Clouds reflect light back to space; snow/ice/water/sand also reflect light (and in fact nearly anything else provided reflection is mentioned). One mark each for any two of these. (e) Global temperatures have been rising for the last 25 years and human activity may be responsible. List two components of the atmosphere that may be responsible for this change, and briefly describe the mechanism responsible. (2 marks) Carbon Dioxide (CO 2 ); methane (CH 4 ), Nitrous Oxide (N 2 O), Chlorofluorocarbons (CFCs) are all greenhouse gas. Increased concentrations of these gases in the atmosphere absorb more of the longer wavelength radiation preventing it from escaping into space. Answer should mention both the absorption of radiation and the increased concentration of greenhouse gases. One mark for the two gases; one mark for the explanation of the mechanism.

3 (f) List three important outcomes of global climate change and briefly describe the likely effect of climate change on agriculture. (3 marks) More frequent droughts, storms, floods, changes in the location of agricultural regions; sea levels rising; increased climate/weather extremes, increased evaporation. Agricultural production likely to be degraded (or in some regions improved) by all of these effects. Give two marks for the three outcomes (deducting one for each missed item) and one mark for the effect on agriculture.

4 Question 2 Below is part of a synoptic chart from the Australian Bureau of Meteorology for 17 August Answer the questions below about the situation shown on the chart. (a) What are the contours shown on the chart? What do they connect? What are the units of the numbers shown on the contours? (3 marks) Isobars (one mark); connecting points of constant/equal atmospheric pressure (one mark); millibars (mbar or mb) or hectopascals (hpa) (one mark) (b) Name the region in which the winds are likely to be the strongest. (1 mark) Southern Ocean, south of Adelaide, or south west of Tasmania or Victoria (c) Name a location where the winds are likely to be weak. (1 mark) Northern Australia, winds also likely to be weak over Sydney as well (d) Name two cities through which a cold front will very shortly pass. (1 mark) Adelaide and Perth (half mark if only one given). Melbourne and Hobart are not acceptable. (e) What type of pressure system is just off the chart immediately to the west of the region being shown? (one mark) High Pressure system (f) What is the weather likely to be like in Sydney? (one mark) Fine, low winds (give mark for any appropriate description of fine weather) (g) The city of Hobart is at sea level in Tasmania. Hobart has a tall mountain (Mt Wellington, 1270 metres) immediately next to it. (i) Estimate the atmospheric pressure in Hobart mb mbar or hectopascals (2 marks; deduct one if no units given; 1021 mb or 1023 mb are acceptable as we can not be sure that the pressure varies in a linear manner between the two contours) (ii) The barometric equation P(h) = P 0 e " h / H describes the pressure P(h) at a height h in terms of the pressure P 0 at sea level and the scale height H " 8.7km, where e " is the base of natural logarithms. Using this formula and your result from (i), what is the pressure at the top of Mt Wellington? 883 mb based on 1022mb surface pressure (139mb less than the sea level pressure). Accept +- 1 mb or any answer consistent with Part (i) answer minus (3 marks deduct one mark for missing units).

5 (iii) Assuming that the environmental lapse rate is 6.5 degrees C cooler per kilometre and that the temperature in Hobart is 18 degrees C, what is the temperature likely to be on the top of Mt Wellington? (6.5) = 9.75 degrees C. Temperature in Hobart only quoted to nearest degree and so 10 degrees C is acceptable. (2 marks, deduct one mark for missing units)