We are now well into March, and the air is still quite chilly at times. Yet, if you step outside and stand in the sun for a few minutes, it feels rather warm, and you may even feel the need to take off your jacket. How is it that the sun feels hot in March even though it is cold outside?
Most of it has to do with the sun angle, or the angle at which the sun strikes Earth. This, combined with Earth's specific tilt on its axis in March, can explain why the sun feels warmer, especially when compared to the previous few winter months.
To give more detail, let's first discuss Earth's tilt. The Earth orbits in an ellipse around the sun. However, Earth's distance from the sun in a given orbital position is not determinant of what season it is (the Earth is actually farthest from the sun in its orbit during the Northern Hemisphere summer!) What actually determines the seasons, as well as how hot the sun feels to us at a given time, is how the Earth is tilted on its axis in that moment and therefore the angle at which the sun's rays hit the Earth's surface.
Let's first discuss how Earth is tilted on it's axis during our winter months. Winter in the northern hemisphere typically begins on December 21st or 22nd, when Earth's axis of rotation is tilted a full 23.5° away from the sun. On this day, incoming solar radiation strikes Earth at a direct perpendicular angle to the 23.5° S latitude (the Tropic of Capricorn). Therefore, the sun is generally lower in the sky in the Northern Hemisphere, and its rays strike the Earth at the smallest angle. Because the sun's rays more spread out as they hit the Northern Hemisphere, the amount of energy that hits any given spot is less. This is why the sun does not feel warm or really provide much heat to us during the winter months.
But in March, spring begins on the 21st or 22nd, and at this point, the Earth is no longer tilted toward or away from the sun as it is during our summer and winter months. While the sun in March does not feel nearly as hot as it does during the summertime (when Earth's axis is tilted toward the sun, and the sun's rays strike the Northern Hemisphere at the largest angle), it easily feels warm when compared to winter. It is all because Earth is in the transition from a tilt that points away from the sun to a more neutral position, which in turn, cause the sun's rays to hit the Northern Hemisphere at a more direct angle, providing more energy and heat.
Depiction of Earth's tilt in respect to the sun at the beginning of each season. Image courtesy of NWS Norman, OK.
But, why are air temperatures typically cold in March even though the sun feels warm? This is due to a process known as seasonal lag. Since March in the northern hemisphere marks the end of winter and beginning of spring, we are coming off of the colder temperatures experienced during the winter months. Even though the Northern Hemisphere is indeed warming up in March due to a more beneficial sun angle and longer days, it is just occuring slowly and gradually, as temperatures on Earth's surface takes a little bit of time to "catch up". This is mostly due to the high heat capacity of water, which covers about 70% of the Earth's surface. From more on seasonal lag, check out our blog about Temperatures Extremes & Seasonal Lag.
Sources:
Library of Congress: https://www.loc.gov/everyday-mysteries/meteorology-climatology/item/why-is-it-hot-in-summer-and-cold-in-winter/
Michigan State University: https://wtamu.edu/~cbaird/sq/2013/07/26/why-is-the-sun-cold-in-the-winter/
