COLUMBUS Ohio (WCMH) — Many of us have been enjoying beautiful weather the past few weeks, and being outside, some have noticed and complained online about the smell in the mornings.
While there could be a few explanations of what is causing the smell in spots, we can thank a couple of natural processes that make that smell more noticeable this time of the year, especially in the mornings.
Decaying leaves can add to the smell outside
This time of the year, we are typically seeing more and more leaves hitting the ground, and those are starting to decay, which can cause a musty smell, especially if the ground is full of dew, or is wet. On cool, moist nights, this decaying smell will become stronger to our noses. This will become more apparent on nights when there is little to no wind.
How does the weather help trap the smell
With the warm afternoons and the cool and longer nights, we are getting larger temperature swings each day. The warm afternoons help to accelerate the rate of leaf decay. We have generally had a pattern of abnormally warm afternoons, and seasonal(ish) nights. During the day, the lowest level of the atmosphere where we live heats up to very comfortable levels.
On top of this, our beautiful weather pattern has been one in which has been dominated by high pressure aloft, which indicates sinking air. This gives us the dry, tranquil, and sunny pattern that has been associated with our warm days.
At night, that warm air that we have collected all day, and the buildings, the ground, and associated items release the heat that has been collected and it slowly rises. With the general pattern of sinking air with high pressure aloft, this creates a temperature inversion. This means, that there is an area of the atmosphere that is no longer cooling with height as it normally does.
As you can see in the image above from the Storm Prediction Center at NOAA, this is a sounding from Thursday morning, and you can actually see two temperature inversions. The first is near the surface at about 600 feet above the ground, and another inversion roughly 4,000 feet above the ground. You can see these in the purple circle, where the red line makes a jog to the right (warmer than the air below it)
Temperature inversions happen often and are not uncommon at all, but during this time of the year, we tend to see more of these close to the ground with our longer, cooler nights, and our warmer afternoons. Going back to the high pressure, when in direct influence, we typically do not have much wind either. Winds will help to mix the air more efficiently and will cut down on the likelihood of an inversion forming.
Inversions can cause the air below them to basically be trapped, and not mixed well. So think about smog out west being trapped by an inversion, pollution, a shallow fog layer, or in this case, a smelly layer. The inversion will cause the air in that pocket to essentially recirculate.
As the sun comes up in the morning and begins to warm the ground temps, we will start to see winds picking up during the day, and the temperature inversions near the ground will go away.
As the sun starts to go down, as the air near the surface starts to cool faster than the air above it, the process can begin again.
