Is the air really “heavy” on a humid summer day?

Posted on July 12, 2021 by WeatherGuys Editor

As the baseball season reaches its annual All-Star break, perhaps you have noticed (as we have) that baseball broadcasters are beginning to refer to “heavy” air as the summer reaches its peak.

This “heaviness” is sometimes offered as a warning to fans that they should not expect a lot of home runs on a given night.

The fact that high humidity in the summer can sap one’s energy is a familiar physiological reality for almost all of us, and so it almost certainly has a bearing on athletic performance. This impact, however, has nothing to do with the weight of the air that surrounds us.

As it turns out, the exact opposite is actually true. Even if the air were perfectly absent of water vapor, the warmer that air gets the less dense it gets. This means the air is lighter as it warms up.

In fact, anyone who has thought about why a hot-air balloon works is likely to have come to this conclusion at some point.

If we add water vapor to the air, which is common in summer and accounts for the uncomfortable feel of a muggy day, the air gets even lighter. That is because humid air is a mixture of “dry” air and invisible water vapor. Since the dry air has a molecular weight of about 29 grams/mole (1.29 grams/liter) and water vapor has a molecular weight of about 18 grams/mole (0.804 grams/liter), any mixture of dry air and water vapor drops the weight of air below what it would be were it completely void of water vapor.

Thus, the broadcaster’s suggestion that summer air is “heavy” is physically incorrect.

When you hit a baseball, speed, angle, air resistance, and altitude all affect how far it travels. Click on the image to learn more.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Category: Meteorology, Seasons

Comments Off on Is the air really “heavy” on a humid summer day?

Do car tires protect you from lightning strikes?

Posted on July 7, 2021 by WeatherGuys Editor

Lightning is a huge electrical discharge, or spark, that results from vigorous motions that occur in thunderstorms. While you can be safe in a car in a lightning storm, it is not because of the tires. Rubber tires do act as an insulator but only at low voltages. For comparison, the current in your house is 120 volts and 15 amps, while a typical lightning bolt is about 300 million volts and about 30,000 amps. The voltage in a lightning bolt is too high to be stopped by tires. A lightning strike can blow out your tires or wreck your car’s electronic control circuits.

Inside a car can be a safe place to wait out a lightning storm. If the car is struck by lightning, its metal frame redirects the electrical current around the sides of the car and into the ground without touching the interior contents, including the people inside.

Don’t lean on the doors. The metal frame acts like a Faraday cage, which is a hollow conducting object that protects its interior from electrical fields and currents. Riding around in a convertible, no matter what kind of tires you have, will not protect you, as you are not in a fully enclosed metal cage.

A unique looping lightning bolt captured in Wisconsin by Jerry Zimmer in 2019.

Lightning is very dangerous. About 300 people in the U.S. are injured by lightning each year, and about 62 people are killed. On average there is about one death caused by lightning in Wisconsin annually.

While your chances of getting hit by lightning are only about one in a million in a given year, it is good to keep some safety tips in mind.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Category: Meteorology, Phenomena, Weather Dangers

Comments Off on Do car tires protect you from lightning strikes?

Are heat waves and droughts related?

Posted on June 28, 2021 by WeatherGuys Editor

The ongoing heat wave in the western states is shattering hundreds of high temperature records.

Weekly US Drought Monitor Graphic

The extreme heat has now moved into the Pacific Northwest and threatens some all-time records in Seattle and Portland. Seattle has only ever recorded three days over 100 degrees in the last 76 years, but stood a decent chance of seeing three in a row over the weekend.

This extended heat wave is partly a function of the climatology of the western states, partly a function of larger-scale circulation anomalies particular to this June, and partly a function of the gradually warming climate.

It is quite normal for the elevated, often arid, terrain of western North America to support the development of tropospheric-deep anticyclones, or regions of high pressure. This is because the height of the tropopause, the “lid” atop the lowest layer of the atmosphere, the troposphere, is directly tied to the average temperature of the underlying air column. In summer, it is easy to warm the air columns above mountains and produce a locally elevated tropopause. The resulting anticyclone encourages gentle sinking of air which keeps the skies clear and limits precipitation production.

As the underlying ground continues to dry out in the absence of rain, it warms more each day and temperatures start to climb. The same circumstances intensify drought conditions so heat waves and droughts go hand-in-hand as a matter of course.

Global warming has increased the background temperature fractionally and leads to reduction in snowpack, reduction in summer precipitation, and increased aridity in the mountainous regions of western North America.

So, the current heat wave and severe drought are physically interrelated and are supported by the background warming. All of this puts the region at extreme risk, again, for a prolonged and devastating wildfire season.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Seasons, Severe Weather

Comments Off on Are heat waves and droughts related?

What is the summer solstice?

Posted on June 21, 2021 by WeatherGuys Editor

 The summer solstice marks the longest day of the year.

The summer solstice occurs at the moment the earth’s tilt toward the sun is at a maximum.  Therefore, on the day of the summer solstice, the sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice.  In fact, the word solstice comes from Latin solstitium or sol (the sun) + –stit-, -stes (standing).  (Image credit: weather.gov)

It is an astronomical event caused by Earth’s tilt on its axis and its orbit around the sun.

Monuments such as Stonehenge on Salisbury Plain in Wiltshire, England, demonstrate that ancient cultures knew the path the sun traveled through our sky changed in a routine way throughout the year. They undoubtedly observed that how high the sun appears in the sky varied throughout the year and that the higher the sun gets in the sky, the longer the length of daylight.

Our summer solstice occurs when the sun is directly overhead at noon at 23.5 degrees north of the equator, the latitude called the Tropic of Cancer. This is the farthest north the sun ever gets. This year, the sun reached the Tropic of Cancer at 10:32 p.m. Sunday.

At the summer solstice, the sun reaches its highest point in the sky and daylight is longest. The sun rises and sets farthest north at the June solstice. However, our earliest sunrise occurred on June 14, while our latest sunset occurs about a week later than the summer solstice. So, while the summer solstice has the longest daylight hours, that day does not correspond to the earliest sunrise or the latest sunset.

The time when the sun reaches its highest point in the sky is called solar noon. Solar noon rarely occurs exactly at clock noon — it’s sometimes before and sometimes after noon on our clocks. In June, the day, as measured by successive solar noon, is nearly 1/4-minute longer than 24 hours. Hence, the midday sun, when the sun reaches its highest point in the sky, comes later by the clock on the June solstice than it does one week before. Therefore, the sunrise and sunset times also come later by our clock.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Seasons

Comments Off on What is the summer solstice?

Is hot first part of June a sign of things to come?

Posted on June 14, 2021 by WeatherGuys Editor

A barely colder than normal May has been followed by an extremely warm and dry first two weeks of June.

Through Friday June 11th, Madison had five days with high temperatures above 90 degrees, and the month has thus far averaged more than 11 degrees above normal.

Simultaneously, the dry spring has continued into the early summer with the month of June already 1.69 inches of rain below normal, and that’s after April and May came in at a combined 4.24 inches below normal.

Coincidentally, this week the National Oceanic and Atmospheric Administration (NOAA) reported that the monthly average carbon dioxide (CO2) fraction in the atmosphere, as measured at the top of Mauna Loa in Hawaii, set a new record of 418.92 ppm (parts per million) in May.

This graph depicts the upward trajectory of carbon dioxide in the atmosphere as measured at the Mauna Loa Observatory in Hawaii.
Credit: NOAA Global Monitoring Laboratory

This represents a larger than 50% increase in atmospheric CO2 concentration since the pre-industrial age (1750-1800), when the value was about 280 ppm as measured by analysis of air bubbles in ice cores taken from ice sheets in Antarctica and Greenland. The current value has not been observed on Earth in the last 4.1 million to 4.5 million years, when sea levels were 78 feet higher than they are today and the global average temperature was 7 degrees warmer than at present.

Not even the COVID-19 pandemic was able to put a dent in the rate of increase in CO2, which suggests that, unless we change the nature of our energy use, we are continuing to forge a path toward a very different, and likely extremely adverse, climate future.

Since solar and wind energies are already cheaper than fossil fuels and they work at the scales necessary to power the world, there is no reasonable excuse for not moving aggressively to a more sustainable energy future.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Category: Climate, Meteorology, Seasons

Comments Off on Is hot first part of June a sign of things to come?