I took a half-day trip during spring break (somewhere around the 31st) to the Shaw Nature Reserve in Gray Summit. I was hoping to find some books on native, Missouri, flora and fauna, and see if the Reserve would be a good place for a field trip (they have sleeping facilities so even overnight trips are a possibility).
I found a number of books, including a nice one on mushrooms, and while I could have, I did not pick up one on wildflowers (of which there were several). Of course, spring is the perfect time to see wildflowers, especially since we ended up hiking the Wildflower Trail, so I’m probably going to have to go back sometime soon.
The lady at the main office (where you pay $5/adult) recommended we take the Wildflower Trail and then cut down south to the sandbar on the Meramec River, which is an excellent place for skipping rocks. She also recommended I take my two kids to their outdoor “classroom” for some real, unstructured play.
Without a reference book, I’ve had to resort to the web for identifications, with only a little success, so I’ll post a few of my photographs here and update as I identify them.
The following two pictures are of a flower that was found covering the hillslope meadows; open areas with short grass.
Beautiful reddish-orange blooms on this small herb.This picture better captures the growth form and leaves of this hillslope, meadow flower.A yellow petalled variant.
Like little stars in the daylight, these small, white flowers meadow flowers almost sparkle.
Small, white, meadow flowers.
Pretty, small, yellow, meadow flowers.
Yellow, meadow flowers.
These bent-over flowers can be found on the lower, shadier edges of the hillslope meadows.
These guys like the shadier areas.I love the texture of the charred wooden stump behind the flower. The meadow itself is possibly the result of a burn.
Iris’ were also in bloom.
Small iris.
Another herbaceous, yellow flower.
Pretty yellow flowers.
More, tiny, delicate flowers.
Found in the shadier, moister parts of of the slope.
Once you get under the canopy, you run into some broader leaved plants and their own, interesting flowers.
Bell-shaped flowers in broad-leaved herbs/shrubs.
We ended up spending a lot of time on the sandbar, learning to skip rocks and hunting for clams, but I save that for another post. And we never did get to the play area; that’ll have to wait for the next trip.
We’re studying biomes and I don’t know a better way to consider how they’re distributed around the world than by talking about the global atmospheric circulation system. After all, the primary determinants of a biome are the precipitation and temperature of an area.
Diagram showing global atmospheric circulation patterns.
It’s a fairly complicated diagram, but it’s fairly easy to reproduce if you remember a few fairly simple rules: hot air rises; the equator is hotter than the poles; and the Earth rotates out from under the atmosphere.
Hot air rises
Light from the Sun hits the equator directly but hits the poles at a glancing angle, so the equator is warmer than the poles. Warm air at the equator rises while cold air at the poles sinks.
The equator receives more direct radiation from the Sun. A ray of light from the Sun hits the ground at an angle near the poles so it’s spread out more. More radiation at the equator means the ground (or ocean) is warmer, so it warms up the air, which rises.
The warm air can’t rise forever, gravity puts a stop to that. If we did not have gravity the atmosphere would float off into space (and the universe would be a fundamentally different place). Instead, when the air reaches the upper atmosphere at the equator it diverges, heading either north or south toward the poles.
From all around the hemisphere the air converges on the poles. The air is cooling as it moves away from the equator, and when it gets to the pole it sinks to ground level and then makes the journey back to the equator. It’s a cycle, aka a circulation cell.
Hot air rising near the equator and sinking near the poles creates a cycle, a circulation cell, in each hemisphere. In this picture, the winds at ground level (dashed blue lines) would always be blowing from the poles toward the equator. This is what the world might be like without the coriolis effect.
Standing on the ground, the wind would always be blowing towards the equator from the poles. If you were in the northern hemisphere, in say Memphis, you would always be getting northerly winds.
The ITCZ and the Polar High
At the equator the rising air also takes with it water vapor that was evaporated from the oceans or from the land (evaporation and transpiration, which are together called evapotranspiration). The warm air cools as it moves up in the atmosphere and the water vapor forms clouds.
You get a lot of clouds and rainfall anywhere there is a lot of rising air.
Because air is coming together, converging, from north and south at the equator, and the equator is in the middle of the tropics, the zone where you get all this rising air is called the Inter-Tropical Convergence Zone or ITCZ for short (that’s an acronym by the way). The ITCZ is pretty easy to identify from space.
The line of clouds near the equator shows where air is converging at ground level and rising to create clouds. It's called the ITCZ. (Image via NOAA, which also hosts real-time images of the Tropical Atlantic that show the ITCZ very well).
All the rain from the ITCZ, and the warmth of the equator means that when you go looking for tropical rain forests, like the Amazon and the Congo, you’ll find them near the equator.
Locations of rainforests (more or less). Notice that in addition to the Congo and Amazon, Indonesia is pretty well forested too. All because of the ITCZ.
Now at the pole, the air is sinking downward from the upper atmosphere. Sinking air tends to be very dry, and places with sinking air also tend to be dry (it’s not a coincidence). So although the poles are covered with ice, they actually tend to get very little snowfall. What little snow they get tends to accumulate over tens, hundreds and thousands of years but the poles are deserts, arctic deserts, but deserts all the same.
The region of sinking air near the poles is called the polar high because of the high pressure generated by all that descending air.
We’ll complicate the picture of atmospheric circulation now, but the ITCZ and the polar high don’t change.
The Earth Rotates
The complication is the coriolis effect. You see, as the Earth rotates it kind-of drags the atmosphere with it. After all, the atmosphere isn’t nailed down. It’s got it’s own motion and intertia, and doesn’t necessarily want to rotate with the Earth.
Deflection of the wind, represented by a ball, because of the movement of the Earth beneath it. The ball here moves in a straight line but it appears to curve because the Earth is rotating out from under it. Click the image for a bigger, better version.
So a wind blowing from the North pole to the equator gets deflected to it’s right; the northerly wind becomes an easterly.
I could write an entire post about coriolis (and I will) but for now it shall suffice to say that the low-level wind from the pole gets deflected so much that it never reaches the equator. The high-level wind from the equator never reaches the pole, either. Instead of the one, single, circulation cell in each hemisphere, three develop, and you end up with the picture at the top of this post.
In this diagram, the convention is that it shows the circulation cells along the side of the globe, in profile, while the arrows within the circle of the globe show the wind directions on surface.
Note also that the winds in the region just north of the equator (where the label says “Tropical Air”, come from the northeast. These are the northeast trade winds that were vital to the transatlantic trade in the days of sailing ships. Know about them help a lot in the Triangular Trade game.
The Sub-Tropical High and the Sub-Polar Low
With three circulation cells you add the sub-tropical high, and the sub-polar low to the ITCZ and polar high as major features that affect the biomes.
Remember, rising air equals lots of rain, while descending air is dry.
So the sub-tropical high, with its descending air, makes for deserts. Since it’s in the sub-tropics these are hot deserts, the type you typically think about with sand-dunes, camels and dingos.
Sub-tropical deserts from around the world. They're located in the zones 30 degrees north and south of the equator at the sub-tropical high. Base map by Vzb83 via Wikimedia Commons.
The USGS also has a great map that names the major deserts.
Biomes
So if we now look at the map of biomes and climates from around the world we can see the pattern: tropical rainforests near the equator, deserts at 30 degrees north and south, temperate rainforests between 40 and 50 degrees latitude, and arctic deserts at the poles.
Map of biomes from around the world. The different biomes are closely related to the general atmospheric circulation model. (Image adapted from Sten Porse via Wikipedia)
