Sometimes the tornado wins big

kw: book reviews, nonfiction, tornadoes, atmospheric science, meteorology, storm chasers, biographies

I've never chased tornadoes, but I have seen a few. The number is small enough to catalog:

• 1964, August, Cedar Point, Ohio: A squall line spit out seven waterspouts, one after another, that marched out of Sandusky Bay and crossed the Causeway and Chaussee between the amusement park and the city of Sandusky, then dissipated. Waterspouts are seldom stronger than EF0 or EF1.
• 1985, Summer (July?), Rapid City, South Dakota: 4 tornadoes, all probably EF1, touched down in and around the city. I saw two of them. Looking west out my back door, I saw a funnel forming, ran out to take a picture of it, then found it hard to open the door against the wind. My wife called me to the other side of the house. To the northeast, a tornado was on the ground right across the street, tearing up sorghum in my neighbor's field. It was moving east, and no houses were hit. Driving into town the next day, I saw three buildings. Two were untouched; the third, in between the others, had lost its roof, a metal roof which was curled up behind the building. The barbed-wire fence in front of the buildings was full of fiberglass insulation.
• 1990, Summer (August?), Stillwater, Oklahoma: I didn't actually see this one, it was wrapped in rain. I was visiting a friend when my wife phoned to say the tornado siren near our home had gone off—would I please come home? I kidded her, "It sounds like I am safer where I am, but I'll come right now." All the stop lights were not functioning, and nobody else was on the road. As I turned onto the main drag that runs north through town, it began to rain so hard there was soon surf in the middle of the street. When it began to hail, I turned into a parking lot up against a large store, to its south. I tuned to a Tulsa station (the local station was off the air), just in time to hear them say, "We have it on radar, it is crossing Perkins at McElroy." I said to myself, "That is where I am!" The store was on the southeast corner of that intersection. The tornado was actually half a block to my north, taking the top floor from a row of two-story apartment buildings and piling up their A/C units in land to the east. It also broke off a dozen or more power poles around ten feet above ground level, so it was a "skimmer", not quite on the ground yet. I saw all this after the sky cleared, about two minutes after the radio announcement. I made it home safely.
• 1994, June, near Colby, Kansas: We were on our way to Denver from Stillwater. Our son was 7 at the time. Highway I-70 had just hooked northwest, several miles west of Grinnell. Perhaps 10-15 miles ahead we saw a squall line dropping a tornado, which traveled across the road and then dissipated. Another soon followed, and then a third. Then the storm itself broke up. I had slowed down, expecting we might have to stop before getting near the storm. We got to that bit of highway about 15 minutes after the last tornado collapsed and the sky had cleared. There was about a half mile of wet highway, with some torn-up ground on both sides. These were probably EF1 tornadoes. Though that is "weak" compared to the monster EF4 and EF5 storms, an EF1 can still roll a car around until there is too little room left inside for you to stay alive.

What is the tornado scale? The "F" or Fujita Scale was developed by Theodore Fujita in 1971. It was originally a 13-level scale of wind speeds, derived by the formula (V = wind speed in mph):

V = 14.1(F+2)^1.5

Dr. Fujita didn't expect F numbers greater than 5 to ever be used. So far, none has. This formula produces this table of the minimum wind speed for each F number:

• F0 = 40 mph
• F1 = 73 mph
• F2 = 113 mph
• F3 = 158 mph
• F4 = 207 mph
• F5 = 261 mph
• F6 = 319 mph

The "EF" or Enhanced Fujita scale replaced the "F" scale in 2007, with the threshold velocities changed to account for improved research into the kinds of damage caused by various wind speeds. The six thresholds (there is no EF6 or higher) are 65, 85, 110, 135, 165, 200. There is no corresponding formula, but a geometrical analysis indicates to me that a theoretical EF6 region should begin at about 235 or 240 mph and EF7 at about 285-290. This is important for what follows. But let it be said, an EF5 tornado can rip the slab of a house right out of the ground, and even pull some basements up, so there is little point in assigning larger numbers without measurement. When a tornado leaves nothing behind but plowed ground, you're already off the charts!

The Man Who Caught the Storm: The Life of Legendary Tornado Chaser Tim Samaras, by Brantley Hargrove, is a very exciting, fascinating, and ultimately rather sad, biography of Tim Samaras. The author is an excellent journalist, who dug into his subject to the point that he participated in several storm chases with friends of Tim, and witnessed some awesome tornadoes in the process.

Tim Samaras exemplifies the self-educated genius. Classroom study was not for him. With his parents' encouragement, he began taking apart various appliances and electronic devices from an early age. Sometimes he could get them back together. By the time he needed paying work, he was such a valuable instrument inventor and repairman that he was hired in spite of having no college. He cut his professional teeth designing and running instrument packages that could, for example, measure the blast force of two tons of ANFO, the explosive that Timothy McVeigh used to destroy the Murrah Building in Oklahoma City in 1995 (an explosion I felt from 75 miles away).

Tim was also a weather fanatic, and took to storm chasing very early on, teaching himself the meteorological knowledge he needed to forecast where a storm would produce a tornado—or a row of them—and how powerful they were likely to be. From 1999-2001 he developed the HITPR, the first instrument package to survive a direct hit by a tornado core and record the central pressure and temperature profile. He called it "the turtle"; its shape was designed to hug the ground better and better as the wind grew stronger. Its first success came in 2003 in Manchester, SD.

Other successes followed, in spite that the funding he was able to attract was rather poor compared to some other "professional" groups. He continued to get measurements nobody else could get, right up until the end. This was in part due to his superior forecasting abilities, knowing which way a storm was likely to turn, so he could deploy one or more turtles (or successors thereof) and get out of there alive. In one case, the tornado core hit his device 15 seconds after he had turned it on!

His son Paul became a leading photographer and videographer for his work. Thus it was, that when his on-the-spot forecast was not spot-on, May 31, 2013, near El Reno, OK, he, his son, and a close friend, meteorologist Carl Young, were killed by an EF5 tornado. Its official wind speed, measured by others with radar near the time of his death, was 295 mph. The highest wind speed measured for the El Reno tornado was about 305 mph, the second tornado in history to exceed 300 mph. Here is where my estimates above are meaningful: if there is any meaning to the extrapolation I made, this was really an EF7 tornado, and by the older scale, nearly an F6. At the time Tim was killed, its "core" was 2.3 miles wide. The core is defined as the area within which wind speeds exceed 110 mph, at least for tornadoes EF2 and stronger. To people on the ground and comparatively nearby, who survived, it looked like an upside-down mountain, stuck in the Earth. To anyone closer than about a mile away from its outer edge, it seemed to fill from horizon to horizon, and hang overhead like a rippling cliff.

The following image, clipped from a YouTube video by Dan Robinson, shows the tornado from several miles away. Its visible funnel is "only" about a mile wide at this point, but the smaller funnel to the right is a suction vortex that shows the actual width of the whole storm. This vortex, if I read the book right, was itself moving around and around the core at around 100 mph, and had its own winds in the 150+ mph range. Thus the outer edge of that vortex—or one like it—would be the source of the extreme winds that approached and probably exceeded 300 mph.

Largely due to the work of self-educated engineer Tim Samaras, meteorologists and physicists are puzzling out the workings of these storms that produce most violent winds on Earth. RIP Tim Samaras and Paul Samaras and Carl Young. I am sorry you are gone. May your legacy continue. And much thanks to Brantley Hargrove for bringing their story to us, particularly folks who may never see a tornado for themselves.

Doing something about the weather

kw: book reviews, nonfiction, meteorology, history

There it is, at the lower left of the red blotch, a classic hook echo. That is the radar signature of the May 3, 1999 Oklahoma City tornado-laden supercell. This image is from a descriptive web page here, which includes more images and storm maps of the fifty-tornado outbreak that day. This particular tornado developed into an F5, the strongest class of tornado, with winds in the 250-mph (400 kph) range. Its path of destruction on the ground was a mile wide.

More than 100 years ago, Mark Twain wrote, "Everybody talks about the weather, but nobody does anything about it." Mike Smith is one person who has been doing something about it, for decades now. As he writes in Warnings: The True Story of How Science Tamed the Weather, from a "beginning involving spare World War II leftovers, we have developed an effective and highly cost-effective system that saves lives and dollars, nearly every week." He is writing about the system of weather tracking radar, weather spotting persons and equipment, and meteorology professionals that work together to forecast and warn of severe weather wherever (in the US) it occurs.

While weather modification has so far been pretty much a failure, the watch and warning system that Smith and others developed since the 1960s is a great example of doing what you can do. In this case, if you can't change the weather, at least you can get out of the way.

Starting at age five when he and his family lived through a tornado in their Kansas City, Missouri neighborhood, Mike Smith knew he wanted to study the weather. As time passed, he witnessed firsthand the devastation that results when severe weather hits without warning. For many years, the official stance of the National Weather Service was not to mention words like "tornado", so as to avoid panic. There was a ban against it. Then in 1955, the town of Udall, Kansas was hit by a nighttime tornado that pretty much erased the town, killing 82 and injuring 260 of the 500 residents. It is called the "town that died in its sleep." Not long after that, on-air meteorologists issued a tornado warning, and the ban began to lift. It didn't take long to find out that most people don't panic; they take a warning well and move to rescue themselves in a remarkably calm way. The warning system gradually developed into today's graded messages, where a "watch" means severe weather is forecast to arrive soon, and a "warning" means it has been seen.

Smith recounts story after story of the gradual shift in attitudes, and of the developing technology. Early radar equipment, scavenged from WWII salvage yards, was able to show you the location and size of a storm, as long as the rain wasn't too strong right around the antenna. It worked best from about fifty miles away, but later problems showed that forecasters need to be where the screens are. Co-location of equipment and forecasters has been the norm for more than twenty years. The development of doppler radar in the 1980s was difficult enough as a technical and engineering challenge. But the bureaucratic roadblocks were much more severe! The author's disdain for a government's way of doing things forms a heartbeat of the book.

This thread is strongest in the chapter about Hurricane Andrew and the three chapters devoted to Hurricane Katrina. Andrew showed us just how damaging a Category 5 hurricane could be. Katrina showed us that the "powers that be" had learned nothing from Andrew. Smith is particularly disdainful of the criminally inept performance of the two governors and the New Orleans mayor. Come to think of it, this is the only major piece of writing about the Katrina disaster that puts the blame where it lies, rather than mostly upon President Bush. Though he does get his share of the blame, the President was a lesser player next to those who should have acted and either did nothing or actively hindered those who were willing to help!

The book ends with the tragic but heartening tale of the destruction of Greensburg, Kansas in 2007. This was another F5 tornado like the one that hit Udall. It was 1.7 miles wide; so was the town, and the tornado hit dead center, as the Udall tornado had. Proportionally (Greensburg's population is 1,500), more than 240 people could have died. The death toll was eleven, and injuries were also few. What a difference a few decades of progress have made!

Until somebody invents the Handy Dandy Hurricane and Tornado Stopper and Flood Tamer, the best we can do is to take heed to warnings and get out of the way. Our ability to obtain warnings and other weather data, now at the click of a mouse or flick of a 'phone, is due to the efforts of Mike Smith and his colleagues over the past forty-plus years. I wonder what the next forty will bring?

Blue sky from above

kw: photographs, meteorology

This image is a small clip from a large satellite image found at www.raize.ch, titled "High resolution satellite images of the Yecheng-Western Tibet-Kathmandu-Highway 219".

What piques my interest here is the deep blue tint of the shadows that run diagonally from top left. We are seeing blue sky from above! This is not seen in most satellite images for two reasons: firstly, the vertical relief in most images is small so any bluing of the image is automatically corrected for in the camera, and secondly, there are seldom these deep shadows that allow the blue reflected from the sky above to dominate.

This reminded me of a question I've seen a time or two: "Is the sky blue for planets around stars of different colors?" The answer is, it depends. The sky of Mars, for example, is pink because there is always suspended reddish dust, and the air column is 1/1000th that of Earth. Any blue light scattered by Mars's air is correspondingly fainter and the dust color dominates. But if there were no dust, the sky would be blue, though a very blackish blue.

Now, how about an Earth type planet orbiting a "blue" or "red" star? Clear air takes the light that passes through it and scatters a small proportion of it via Rayleigh Scattering, for which the amount scattered varies as the fourth power of photon energy. Thus, blue with wavelength 450nm is scattered 4.4 times as much as red light with wavelength 650nm. So no matter what the spectrum is of the light passing through a clear gas, the light scattered at right angles will be much bluer. Of course, for a blue star, the light is already blue, and just gets more intensely blue. For a "red" star, we need to realize that even a very cool M9 star is hotter than a carbon arc, which itself is quite a bit hotter than the "whitest" tungsten filament lamp.

There is a contrast effect at work here. The Sun is considered the standard of whiteness by astronomers. The sun's surface temperature is close to 6,500K. Its actual color is rather bluish, compared to the color we see after its light has passed through the atmosphere. Even on the clearest day, at elevations near sea level more than one-third of the light has been scattered, removing lots of blue, so that it has a spectrum more like something at a temperature below 4,000K. There are complications, because stellar gases don't have "flat" emissivity, but I don't want to go into the slight difference between color temperature and actual temperature here.

Any star cooler than the Sun will look yellow or orange by comparison. But the "white" light from a filament lamp (the next generation is likely to forget what they are!) is actually quite reddish, for the filament's temperature is about 2,700K. An M9 star's surface temperature is close to 3,300K, a couple hundred degrees hotter than a carbon arc (used in old-fashioned movie projectors and in searchlights).

If you focus a lot of the "white" light from a tungsten lamp into a beam passing through clean air, and look at the scattered light with a sensitive camera, it will be quite blue. Thus the sky for an Earth type planet around any star will appear blue. If any planet has a green or purple sky, it is because something in the air is changing the spectrum; there's no getting green or purple from a thermal spectrum just by Rayleigh scattering.