Q: Why are some clouds flat on the bottom and grouped perfectly at the same altitude?
Jason Satterlund, Nashville, Tennessee
A: It's simple: Try visualizing the Great Plains on a sultry August day. With temperatures in the mideighties and relative humidity of 45 percent, air will cool to 59 degrees when it rises a vertical milethe right combination of conditions to cause vapor in the air to condense and form perfectly horizontal cloud bases at exactly that altitude. The cauliflower-shaped cumulus clouds then billow up on rising air currents, but even as they do, more vapor reaches the mile-high starting point and refreshes the base with new droplets. The cycle continues as long as a reflective heat sourcea field or tropical island or strip-mall parking lotkeeps generating a warm column of rising air. "I was once stranded on the runway at Homestead Air Force Base south of Miami, waiting for President Nixon to take off in Air Force One," says Peggy LeMone, a senior scientist with the National Center for Atmospheric Research. "The cumulus clouds above us didn't move for an hour because of the hot tarmac and calm high-altitude winds."
Q: If a person is acclimatized to high altitude, how quickly is the acclimatization lost if he descends to sea level? Greg Rossell, Grover, Utah
A: Several factors affect the speed of deacclimatization, chief among them the length of time spent at altitude. In general, the longer you've been at altitude, the longer it takes for the effects to wear off, and the longer you'll feel like a superhero at sea level. For folks who reside permanently at moderate altitudes (technically, high altitude is defined as anything above 8,000 feet), the process happens gradually over a period of several months, with the most noticeable effects taking place in the first six weeks. The minute you descend even a couple hundred feet from the mountains, you'll begin to breathe more easily because at high altitude you produced up to 25 percent more red blood cells than your lowland competitors. These cells transport oxygen to your muscles and brain with remarkable efficiency, but unfortunately, at sea level they die in about two weeks, and the natural blood-doping effect wears off. Even then, you'll still feel stronger than normal for four more weeks because your muscles adapted to performing with low oxygen but are now enjoying high-octane sea-level air. They're receiving more bloodfrom extra blood vessels produced at high elevation. They're burning more fuelthanks to muscle cells with extra mitochondria, microscopic factories that release energy from food, made at high altitude. And they're accepting more oxygendue to an elevation-enriched number of O2-transferring enzymes. In short, your muscles can go faster, longer, and harder; but incrementally less so as the blood vessels, mitochondria, and enzymes slowly disappear. At which point you're a mere mortal.
Q: Why do gnats form swarms that hover just at human eye level?
Patrick Ackerman, Madison, Wisconsin
A: Think of that swarming mass of bugs as one wild fraternity party. "Gnats live to mate," explains Kent State University entomologist Benjamin Foote. "Their only purpose is to pass their genes to the next generation." Over the course of several million years of evolution, these midges (or "lower flies," as they are called in entomology circles) have figured out that a swarm is by far the most effective midge-ette magnetthe simple reason being that, given your average midge's two- to three-day life cycle, finding a mate is more likely in a teeming throng. Hundreds of males amass in a pack at sunrise and sunset; while it may seem that midges always choose to hover at eye level, the gathering height, anywhere from six to 50 feet, depends on the species. As the swarm grows, females take notice and fly into the buzzing orgy, and males, capitalizing on the chaos, use a pair of infinitesimal muscles to latch on to their feminine guests. As is the case with frat parties, though, a big gathering doesn't ensure intimate congress. "I estimate 10 to 20 percent of the males accomplish their goal," says Foote.
Q: As an avid open-water swimmer, I have to ask: What causes cold pockets in the ocean?
Rick Walker, Sarasota, Florida
A: Rest easy, cold pockets have nothing to do with the Marianas Trench, the Bermuda Triangle, or the mysterious bodily functions of fish. They are, however, associated with the Roaring Forties, westerlies, trade winds, and other types of strong breezes. That's because two factors team up to create cold pockets: wind and sun. Sunlight heats the top few feet of water to as much as eight to ten degrees Fahrenheit above the temperature of the water below, and wind creates waves. The balmy surface mixes with the teeth-chattering depths andvoilÃ cold stashes emerge from the nonuniform stirring. One way to avoid them is to swim closer to shore. There, surf and riptides constantly combine warm and cold layers into one reliably tepidif somewhat turbulentlap lane. Just mind the breakers.
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