Congratulations, you've made it to week two of the online course! In this second week of HPW online, we build on the "bare rock" model Earth presented in Week 1, and add (an) atmosphere. This leads us to look at how scientists understand light and air. Dunsfort will show us how the interactions of these two things help us understand everything from why the sky is blue, to why sunsets are beautiful, and why the Earth is not as freezing cold as we calculated it should be, last week.  However, a static atmosphere alone would result in a world that's far too hot. To get more comfortable temperatures, we need the atmosphere to move. Dr Kabir will guide us through how and why the atmosphere in is motion and what that means for us.

Remember that at this point we ONLY have solid Earth and atmosphere in our model discussed in the Core Lectures - nothing else as yet. 

That being said, following this week's Core Lectures, we take a side step with our first Key Lecture (an invited speaker that does not form part of the main story) and start to consider one of the most unusual and complicated aspects of Earth Systems Science: Humans. We deal with these unusual, and rather unpredictable, primates in more detail at the end of the Core Lecture course. But for now, I would like us to start thinking a little more about what happens when science and humans interact, as they inevitably do in Earth Systems problems. It's important to start thinking about this early, as it is one of the main themes of the course and frames how we view the science presented. However, this does not mean we have added humans to our model Earth, just yet. 

1. This week's Lectures

3. Special South Africa

As Dunsfort discussed, South Africa has a special advantage in learning about the atmosphere: mountains that rise majestically from the sea. This is quite rare in the world and provides the idea platform to ascend from sea level, up through the atmosphere, and measure physical changes (see pictures below).

South Africa is also special when thinking about the Hadley Circulation that Kabir told us all about. Prof. George Philander tells this story better than me, he says:

“First consider a water covered globe. [As Kabir has already told us] …the air will rise at the equator and, if the Earth did not rotate, then the air will travel poleward aloft, will sink at the poles, and will return equator ward near the surface. On a rotating Earth, the air aloft moving poleward is deflected eastward by the Coriolis force so that we get the intense Jet Streams (westerly or eastward winds) in midlatitudes. Furthermore, the poleward flowing air aloft radiates heat to space, cools off, and some of it sinks to the surface around 30 degrees latitude which therefore are deserts. Once at the surface some of the air returns to the equator and some flows poleward. The equator-ward flowing air at the surface is deflected westward by the Coriolis force. So now you have Hadley Cells between the equator (where air rises) and 30 at where the air subsides and you have easterly trade winds in the tropics, but westerly winds further poleward. So on a water covered globe, South Africa is near the boundary between easterly and westerly winds. That boundary moves N-S seasonally “

The result is that, thanks to its position at around 30S, South Africa experiences a much great range of climates than almost anywhere else in the world. This is both a great seasonal range at a given location, but also a great range of climate between different locations. 

For more information see:

http://www.sanparks.co.za/parks/table_mountain/

Secondly, we asked one of the country’s brightest young atmosphere scientists, Dr Francois, to watch this week's videos and post a critical thinker's response, here is what he had to say:

6. This week's test

Click here when you think you know it all, and want to be tested.

***PLEASE NOTE THAT WE WILL ONLY ACCEPT YOUR FIRST ANSWERS. THINK CAREFULLY BEFORE YOU PRESS THE SUBMIT BUTTON ***

(deadline = Tuesday 17th September)