Warming After Midnight

Occasionally when I look at my weather station I see something interesting. That happened this morning. Usually we expect to see temperatures to fall all night after the sun goes down. That didn't happen last night. At 2:00 this morning the temperature increased almost five degrees! What caused this?...It was the wind!

(c) bkb

Winds were blowing at 2 mph, but were gusting at 8 mph. If you were to stand outside you would feel warm gust of air. 

Wind mixes air from above down to the surface. This brings warmer air in two ways. First, air aloft is usually warmer at night. This is called an inversion. Air is cooled from the surface up at night, and winds can mix that warmer air aloft down. The other way descending air causes warming is because of thermodynamic effects. When air descends it is compressed. As a result, the temperature increases. The nighttime cooling finally took effect after 3:00.

Spanish Fork Wind Rose

A wind rose illustrates wind direction, wind frequency, and wind speed. The direction of each bar shows where the wind blows from. The length indicates how often, in percent, the winds blow from that direction. The colors indicate wind speed.
This is a wind rose I created using a python script I found on the internet. Plotted is wind data collected from my weather station from March 13, 2013 to July 9, 2013.

Spanish Fork Wind Rose

Wind Direction, Frequency (%), Speed (mph)

March 13, 2013 to July 9, 2013 (c) bkb

You can see that 21% of the time winds blow from the South-South-East. This is the canyon wind. Wind blows out of the Spanish Fork Canyon at night. That is why Spanish Fork is such a great location for windmills. During the afternoon, winds blow up the canyon, but it appears winds from the northwest are less frequent.

I admit the location of the weather station is not ideal--a residential area and sandwiched between two homes. Wind channeled between the homes is why winds generally blow in two directions.

During this time period, sustained winds above 10 mph were rare. If we looked at wind gusts we would see higher wind speeds. The highest gusts measured by my station during the period is 28 mph.  

Spanish Fork Wind Turbines (c) bkb

Winds high above the surface are much faster. Wind turbines are built high because that is were the winds are the fastest. Friction near the surface slows down wind. However, for terrain induced flows, such as a canyon wind, the temperature gradients near the ground are what causes the winds. There is what is called an "exit jet." The fastest winds at the canyon entrance are probably 10-20 meters above the surface where there is less friction and where the driving force is still great. Placing those wind turbines in that jet will capture the most energy.

WX at KBKB

I made this blog as a place for me to put my thoughts about weather. It's a weather journal of sorts. If you aren't a meteorologist it would be good to know that WX is the abbreviation for "weather." KBKB is my call sign that I assigned myself--kind of like a nickname for my home weather headquarters.

Earlier this year I purchased a Davis Instrument Vantage Pro2. Weather data is automatically uploaded onto the internet on several websites, but I prefer using Mesowest. You can click the image below to get weather data in Spanish Fork.

A little more about me (from my SARP 2013 get-to-know-you poster):

Los Angeles Air Quality

As part of NASA's Student Airborne Research Program I am looking at meteorological influences on high and low ozone days. I've downloaded data from the EPA's website and put together the following plot using Python. It shows the number of days in each Air Quality Index (AQI) category for the last twenty years.

(c) bkb

The colors represent the number of days LA exceeded the EPA's health standard: 75 ppbv. Over the last twenty years there are fewer days with unhealthy levels. The number of days with 'very unhealthy' air is practically zero.


Here is a plot showing the AQI for each day in 2012:

bkb (c)

Notice that the winter months only have good ozone AQI days. This seasonal trend is noticeable during all years. Ozone forms photochemically in the air when other pollutants react in the presence of sunlight. This explains the low ozone concentrations during the winter months. There is not sufficient energy from the sun to make the ozone form. The daily solar energy is lower during winter months for two reasons. First, days are shorter. And second, the earth's rotation is tilted away form the sun causing sunlight to spread over a larger area.

In comparison here is a plot of ozone AQI values for Salt Lake City in 2012: 

bkb (c)

Again, we see low ozone concentrations in the winter months. (Notice that there is missing data in October and December.) Salt Lake does not have many days that exceed the EPA's National Ambient Air Quality Standard (NAAQS). There are two other factors that can causes the difference in these two cities: emission amounts or type, and weather.

Salt Lake, however, has other pollution problems they deal with. Particulate Matter smaller than 2.5 microns, otherwise known as PM 2.5, is the troublesome pollutant along the Wasatch Front. Unlike ozone, PM 2.5 doesn't seem to follow an annual trend. Not shown in this chart is a long polluted episode throughout January 2013. A strong inversion kept air near the surface. The mountains act as barriers that prevented the pollution to mix away. Meteorology, topography, and emissions play a large role in PM 2.5 concentrations in Northern Utah. The year 2012 was fairly unpolluted, but the beginning of 2013 had several days with very unhealthy air quality. Those episodes occur during periods of strong inversions.

bkb (c)