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http://www.atmos.washington.edu/academics/classes/2013Q1/380/HW7.html Due Thursday Feb 28 |
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In this exercise you will learn even more about how fortunate we are to have a well behaved planet. We will analyze in more detail a few of the runs we did last week with planets of varying obliquity and a new run that is tidally locked. We will look at atmospheric heat transport. The tidally locked planet rotates once every 365 days, which is 365 times slower than the obliquity experiments. No new runs will be done this week. Begin your homework write-up with a paragraph explaining the purpose of this exercise. You may need to do each step first. Make a supdirectory for this exercise's analysis files. Maybe you would like to call it "weirdplanets". Go to that directory and copy the analysis files to your directory for this exercise. Start matlab cp /home/disk/p/atms380/scripts/ex7* . matlab & I recommend that you run each script first and get a feel for the exercise before getting into the details a) Run ex7_a.m in matlab. You are looking at daily or nealy daily output from the planetary runs for January. Look for storminess or atmospheric eddies in the variables. Which model has the most eddy activity. Eddy activity depends on horizontal temperature gradients and rotation. Eddy activity can be seen easily as noisy, turbulent behavior in any of the fields in this script. To turn in: Compare and constrast the daily varying structure and motions. Which of the three planets has the greatest eddy activity? Of the two not tidally locked planets, which has the greatest pole-to-equator temperature gradient? Is the eddy activity of the two tidally locked planets consistent with their difference in temperature gradient? b) Run ex7_b.m in matlab to examine a variety of fields, many in height-longitude right along the equator. Run the script for all three choices G, M, and 0 (that's a zero). Between G and M, which one has the largest temperature gradient between light and dark sides of the planet? Which has the most precipitation? Does the one with more precipitation also have more cloud cover? G and M planets each have the same incoming total SW flux but note which one has more net SW flux at the TOA and surface. This is an indication of which star's spectrum G or M is more strongly absorbed in the atmosphere by water vapor primarily. Which one is it? Now given the higher absorption throughout the atmosphere, which one do you expect has a more stable temperature profile (less negative temperature gradient with height)? Is this also the model with less precipitation? Does this make sense to you? Now look at the TOA fluxes. Notice that the TOA net LW is fairly uniform along the equator. How can this be? (hint, LW is strongly emitted from the surface and from clouds) With your answers above mostly focus on G versus M but weave in results from the zero tillt planet as well, which is more like Earth's orbit. c) Now you hopefully have seen that G or M has a weaker temperature gradient. And that both tidally locked planets have weaker eddies than the zero tilt planet, yet the dark side of the tidally locked planets is not absurdly cold. This is because there is high heat transport by the atmosphere from the light to dark sides. Likewise there is heat transport in the zero tilt planet towards the poles. Please focus on the total heat flux. The net heat flux total = sum ( TOA net flux - surface net flux) latent = sum ( surface latent heat flux - precipitation rate * latent heat of condensation - snow rate * latent heat of fusion) note this is like evaporation minus precipitation with coefficients to make the units W/m2 dry = total - latent To help visualize the heat flux we sum either along latitudes or longitudes. Run the script for the zero tilt planet. For the zero tilt planet it doesn't make much sense to sum along latitudes, but we do it anyway to compare with the tidally locked planet. Try not to worry about the funny wiggles in Fig 2. How does the magnutudes of curves in the two figures compare? The curves in Fig 2 ought to be zero if the model is in steady state. Why? It is not quite because there is sea ice growing and snow stacking up on the sea ice ad infinitum at the poles. Hence the small ~2W/m2 offset is an indication of the amount of heat loss that results in growing sea ice and snow depth on this planet. Fig 1 is the more classic text book figure with total that easily indicates where the planet receives a surplus of heat and where it receives a deficit. Run the script for the G and M planets. How does the magnutudes of curves in the two figures compare? This time none of the curves are expected to be zero, why? Notice the sums printed at the end. Which planet has more net heat flux on the Dark side (less negative)? This heat is coming from the light side where the net heat flux is positive. Does this make sense with the relative temperature difference between light and dark sides? The magnitudes of total heat flux along latitude circles for the tilted planet are much larger than the magnitudes of total heat flux along longitudes for the tidally locked planet. Does this seem reasonable given the strength of eddies that you observed in part (a)? Discuss your answers in about a page of typed text, single spaced. Include a few of your favorite figures.
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