How Does Summer Turn to Fall?

By Rebecca Fleeman

Photo Credit: PxHere

As a Florida girl, born and raised, I am often asked why I chose to attend graduate school in Pennsylvania, a state with cold and snowy winters. Family, friends, and colleagues immediately ask, why I would leave such “vacation-type” weather, then quickly follow up with “so, do you plan to move back after you graduate?”. People from up North love the idea of warm beaches year-round and are often envious to hear my stories of wearing shorts every Christmas.  Therefore, it is a little ironic that I chose to move 1,000 miles north of my sunny hometown on the east coast of Florida to ultimately, trade in my flip flops for snow boots.

It is true, I hate the cold weather. I dread the first day of fall when the temperature falls below 60 degrees. It means that outdoor runs will become treadmill runs in the gym and that Saturday outdoor Spikeball tournaments with frozen drinks will become indoor game nights with hot chocolates. As the temperatures have started to drop into the 40s in Hershey, I became curious about how the weather actually changes. We were all taught about the change of seasons in primary school.  We learned about how the Earth’s tilt and rotation around the sun results in more or less sunlight, leading to the changes in weather. But now, as an even more curious grad student, I want to know, how exactly does my wonderful 80° F day turn into a frigid 40° F morning?

What affects temperature?

Two key factors affecting temperature are latitude (angle of degrees north or south of the equator) and proximity to a body of water1. Your latitudinal location changes both the angle of the sun’s rays and the number of daylight hours, thus increasing or decreasing temperature from solely the effect of the sun. My location in Florida was roughly 28 degrees north of the equator while in Hershey, PA, we are about 40 degrees north of the equator. This increased angle leads to less direct sunlight in Hershey, and thus colder winters. Additionally, because water has a high heat capacity, land surrounded by oceans have a reduced temperature flux. A cool science fact: water has the second highest heat capacity of all liquids (trailing only liquid ammonia)2! This is because of water’s covalent bonds between two hydrogen atoms and an oxygen atom. The strong bonding between the oxygen and hydrogen allow water to resist molecular motion, thus making the water more difficult to heat up or cool down as quickly as on land.

How does the temperature actually rise?

Diving a little deeper, how is it that the heat from the sun actually travels through the vacuum of space and causes the air around us to increase in temperature? Or, in the case of Pennsylvania, why doesn’t the heat travel enough for me? The main way the sun heats the Earth is through radiation3,4. Nuclear fission in the core of the sun causes the sun to emit millions of watts of energy in the form of electromagnetic radiation, some of which hits Earth5. We see this radiation energy in the form of visible light6. Remarkably, most of this solar energy is actually absorbed by our atmosphere, and never manages to hit the Earth’s surface6. Some of the energy is even reflected off the atmosphere, back into space4. What radiation does hit the Earth’s surface can then be absorbed and converted to heat4. Once the surface receives the sun’s solar radiation, this energy can be transferred by way of conduction (heat transfer through solids, think a soup spoon) and convection (heat transfer through liquids, think boiling water). Compare Earth and the sun to yourself, sitting in front of a fire, roasting a s’more. The front side of your body is quite warm, due to the fire, but your backside is still cold. The heat is not traveling through the air much to warm your front side. Instead, you are receiving radiation from the fire on your side which faces the fire, warming you. The light energy emitted by the campfire turns into heat energy as it is absorbed by your body.

So, there you have it, a quick blast from the primary school past, with some new fun facts on how the sun warms the Earth. Here in Hershey, PA, we are beginning to see a lack of these warming effects due to the tilt of the Earth in its rotation around the sun, and Hershey’s lack of proximity to warm ocean waters. Climate change is putting an interesting spin on the normal heating and cooling patterns of the Earth, but that is a whole other story. For now, let’s hope we make it through our first snow, and if you’re me, hope that there won’t be too many snow days this year.

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