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Berkeley GEOG 40 - Lab #3_ GHGs and Atmospheric Structure-3

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Name:______________________ Section: __________________ Lab 3 – Greenhouse Gasses, Atmospheric Structure, and Water in the Atmosphere If a problem involves math, please show your work. Part 1. Earth’s energy balance Open the greenhouse demo on PHET (use the browser compatible version) at https://phet.colorado.edu/en/simulation/legacy/greenhouse and answer the questions below. Recall the one-layer-atmosphere model in lecture 4 (Planetary Energy Balance II, slide 20-23). Note that within the atmosphere, at the surface, and at the top of the atmosphere, energy balance has to hold. 1.1 Use these settings (right panel): Atmosphere during Today, 0 number of clouds, thermometer in Celsius, and uncheck the View all photons option. Follow the motion of the shortwave photons (in yellow), and the infrared photos (in red). Explain what happens to each? [3] Without clouds, the shortwave photons (visible light & ultraviolet radiation) emitted by the sun are absorbed into the surface of the Earth, heating it up and causing the Earth to then reemit infrared photons back into space. However, the infrared photons are absorbed and re-emitted by GHG in the atmosphere which cause some to reflect back and some to return to space. 1.2 Wait until surface temperature (the value of the thermometer) becomes mostly stable. What is the equilibrium surface temperature in this setup? [1] Around 13-15 celsius. 1.3 Now click Atmosphere during the Ice age. What do you notice about the trajectory of the shortwave photons that is different from before? Is the surface temperature cooler or warmer than Today, and how does the altered behavior of the shortwave explain the temperature change? [2] The shortwave photons emitted by the sun are partially reflected back into space on areas of the Earth’s surface covered by ice, which have a high albedo, rather than being fully absorbed by the Earth’s surface in darker areas. The surface temperature is cooler, and the decrease in shortwave photon absorption is a large factor since some are being reflected rather than absorbed causing an overall decrease in surface temperature. 1.4 Name one other factor that you think might account for the difference in surface temperature (HINT: note that the atmospheric composition for each simulation is shown on the right side of the demo screen; compare that Today). [1] In addition to the reflection rather than absorption of a portion of the sun’s shortwave photons, the atmospheric composition for greenhouse gases for today is much higher than the GHG atmospheric composition which causes the temperature for today to be much higher. To begin, the amount of water vapor H2O is 0 during the Ice Age, because theatmosphere is at such a low temperature that water vapor is unable to exist (similar to in the South Pole today, where water vapor atmospheric levels are at a .00001% concentration). Because water vapor has a high specific heat capacity, it is able to warm the atmosphere by retaining heat from forms of radiation and increasing humidity. In addition, GHG CO2, CH4, and N2O all increase dramatically when switching from Ice Age to today’s atmospheric composition. The increase in GHG prevents heat from the ground from escaping since these GHGs allow visible light and short wave radiation to pass through, but does not allow Earth’s infrared energy (longwave radiation) to pass through and heat is trapped. This is known as the greenhouse effect, and so thus with increased GHG in atmospheric composition the more amplified the GHG effect becomes and the warmer the temperature. 1.5 Adjust greenhouse gas concentration by moving the cursor to ‘None’. How does the behavior of the infrared photons change as a result, and why? Is the surface temperature cooler or warmer, and explain why based on the behavior of the LW radiation? [2] When the GHG concentration is set to none, the greenhouse gas effect (as explained above) is lost and all of the infrared photons are able to escape to space without barriers, rather than being trapped by any potential GHG that would have existed. As a result, the surface temperature is much cooler (around -18 to -19 degrees celsius) because LW radiation is able to pass through, but with GHG they are often reflected back to the surface causing what would have been an increase in temperature. 1.6 Click back on Today, wait for the temperature to stabilize, and then add 3 clouds. From your observations, describe what clouds do to shortwave, and then separately with longwave radiation. For each of shortwave and longwave, also mention whether it is a cooling or warming influence on the surface. [3] The addition of the three clouds affects SW radiation by causing some of them to reflect back into space (due to thick cloud’s high albedo), allowing less overall SW radiation to reach the surface of the Earth. This would cause a cooling influence onto the surface. Meanwhile, the accumulation of clouds amplifies the GHG effect and causes LW radiation being emitted from the surface of the Earth to reflect back and so less LW radiation is able to escape to space. This would cause a warming influence on the surface. 2Part 2. Water in the Atmosphere Use the Clausius-Clapeyron relationship to answer the question. Try to be as accurate as possible when reading off the graph (use the q* scale on the right). q* is the saturation specific humidity (a measure of the maximum amount of water vapor in a unit mass of air). 2.1 If a saturated 1kg air parcel is at 20°C, how much water vapor does it hold? [2] About 15 g/kg of water vapor. 2.2 If the same parcel warms to 30°C, how much water vapor can it hold? [1] About 27 g/kg of water vapor. 2.3 Consequently, what is the relative humidity of the parcel from the previous question? Assume that the amount of water vapor in the parcel has not changed from question 2.1. [1] Because the parcel has already absorbed the maximum amount of water vapor that can be held per unit mass of air, the relative humidity remains at 100%. 2.4. If the saturated air parcel at 20°C was cooled to 10°C, how much water will condense? [2] @ 20ºC -> 15 g/kg @ 10ºC -> 8 g/kg 15 g/kg - 8 g/kg = 7 g/kg of water vapor will condense. 32.5 How much latent heat does the parcel from the previous question release as it condenses?


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