Temperatures in the Lunar Soil and its Radio Emission
Joachim Köppen Kiel Oct. 2017
Some brief explanations
This simulation computes the temperatures and the radio emission by a patch of the lunar surface, situated in the middle of the lunar face as seen from Earth, both during an entire month and during a total lunar eclipse.The lunar soil is heated by the solar radiation. This heats up the top layer of a few mm thickness. Since the soil is not a solid rock, but consists of a loose mixture of dust, sand, and small pieces of rock (called 'regolith') due to the break up of the material by the constant impacts of meteroites, there is very little thermal contact between individual pieces. Hence the thermal conductivity of this material is very low, and the transport of heat from the top layer to the layers below is very slow.
The simulation solves the equations of thermal conduction in a vertical column of lunar soil. For simplicity, we assume that the properties of the material do not vary with depth. The top soil is irradiated by the Sun, either with a constant rate or with the monthly variation as the Sun rises and falls above the patch, or during a total lunar eclipse when the Moon goes through the penumbra and the umbra of the Earth shadow with the resulting blocking of the sunlight.
The plot on the left shows the time evolution of the temperatures in different depths or the radio fluxes at different frequencies. The five curves are marked with different colours, which the user can assign to different depths or frequencies, respectively. The plot on the right shows the vertical temperature profiles.
The controls are the following:
- Soil properties: (the values below are approriate for lunar material)
- density: 3000 kg/m³ is the overall lunar average
- heat conductivity: 0.003 is for powdered basalt
- specific heat: 840 is for basalt
- the tanδ for electric losses: 0.014 is for basalt
- The colours of the five curves are linked to depths or frequencies by the user
- Month: here one selects the illumination of the patch: constant illumination, month, month with eclipse, eclipse in detail (a few hours around eclipse time)
- Temperatures in 5 depths: one chooses the display among:
temperature in 5 depths or radio fluxes (for 5 frequencies) with various ordinate scales. - Computational details:
- time step [h]: the smaller this value, the better is the accuracy, but the slower is the simulation. Note that during the eclipse, the time step is automatically reduced to follow better the detailed evolution.
- plot after n steps: while the time step refers to the internal value to compute the results, we normally do not need to plot every time step, but only every 30th (for example).
- clear after n curves: do avoid cluttering up the plots, it is better to clear the displays after a number of curves have been done, e.g. 10.
- start, stop, resume, clear control the running of the simulation.
- Mouse position: shows the abscissa and ordinate values of the mouse pointing inside the plots
Just a word of caution: Please keep in mind that the accuracy of the results depends on the chosen time step. The smaller this value, the better are the results, but they take longer! The largest permissible value depends on the properties assumed for the lunar soil. If you notice the beginning of a zigzag pattern in the curves (in the left image below), you need a lower time step! Otherwise you may end up with a spectacular pattern (right image) which has nothing to do with the lunar soil, but is simply a numerical fantasy!
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