Monday, September 24, 2012

When the Lights Go Out

One of my readers posed the question: When I turn off the light in my bedroom at night, where does all the light go? Before we answer this, we need to make a few assumptions. Let’s assume that the bedroom is a perfect container: It has no windows for light to escape from and no cracks around the door so light can’t escape there either. Also, let’s say the walls are perfectly solid, and consist of a regular structure of atoms. Imagine a grid of hard spheres laying next to  each other. This is the surface of the walls. 
   First, we need to realize that light is a form of energy. While the light switch is on, it closes an electric circuit and electrons flow through the light bulb. The light bulb converts the energy from the electric current to light energy in the form of photons. Photons are tiny packet of electromagnetic energy and momentum. When you turn the light off, the circuit is broken, the energy stops flowing, and the light goes away. But where does it go?
   The photons travel across the room at the speed of light. When a photon hits the wall, its energy and momentum is either absorbed by the atoms in the wall, or are reflected to another wall where it again may get absorbed or reflected. One of the fundamental concepts of physics tells us that both energy and momentum are conserved, which means that an atom will get a small kick from absorbing a photon. It will move, and kick against its neighbor, etc. If enough photons get absorbed, this will result in the wall warming up slightly. So the light gets converted into thermal energy in the wall. This is what is meant by having a temperature. 
   If the wall were at absolute zero, these atoms do not move and are simply at rest, each one just touching the next. By saying that the wall has a temperature, we are really saying that it contains thermal energy. This thermal energy is the random vibration of the atoms around their equilibrium point. Such a vibration can travel through the grid of atoms in the form of a wave. One atom pushes the next, which pushes the next, etc. 
   When you turn off the light switch, the process just stops—the bulb stops generating photons, and the last set of photons hit walls until they’re all absorbed, all within a fraction of a second.

Monday, September 17, 2012

The Keystone Species of the Southern Ocean

A swarm of krill in the Southern Ocean

Worldwide there are about 85 species of krill, the largest of which is the Antarctic krill (Euphausia superba) which averages about five centimeters in length. Antarctic krill live in dense concentrations in the cold Southern Ocean. At any given time there are four or five billion individuals, and when they congregate for spawning they create a pink swarm so large that it can be seen from space.  
   Krill are crustaceans like crabs, shrimp and lobsters. But unlike their cousins that are bottom-feeders, krill are pelagic—they make their living in the open ocean. And unlike the plankton they feed on, krill are nektonic—they are able to swim independent of the ocean currents. 
The anatomy of the Arctic krill
   Antarctic krill feed on algae and phytoplankton that are suspended in the water column. They are preyed upon by nearly every Antarctic predator that exists. And if a predator doesn't eat krill, it feeds on the ones that do. A penguin's diet consists of nearly 100 percent krill. Blue whales rely on krill for almost all of their dietary requirement. During the summer months, an adult blue whale eats up to 40 million krill in a single day to fulfill its 1.5 million kilocalorie nutritional needs. Antarctic krill is the keystone species in the Southern Ocean, and without it, the ecosystem would collapse.
   Antarctic krill use intensive searching and rapid feeding techniques to take advantage of high plankton concentrations. Krill form dense schools that move horizontally in the water column when feeding. Krill spend their days avoiding predators in the cold depths of the Southern Ocean. At night, they drift up toward the surface to search for phytoplankton.
   Recent studies show Antarctic krill stocks have dropped by as much as 80 percent since the 1970s. Scientists attribute this decline in part to ice cover loss caused by global warming. This ice loss removes ice algae from the Southern Ocean which is a primary source of food for krill. NASA satellite data reveals that there has been continuous ice loss from Antarctica since 2002—more than 100 cubic kilometers of ice per year.

Monday, September 10, 2012

The Skies Near Mount Ranier

Located southeast of Seattle, Mount Rainier is the tallest volcano in the Cascade Range and the most topographically prominent mountain in the contiguous United States. Its summit is at an elevation of 4,392 meters and it has a topographic prominence of 4,027 meters. Because of this, many people from the Pacific Northwest are treated to the spectacular beauty of this snow-capped peak which dominates the landscape. But if you are really lucky, your view of Mount Ranier could be enhanced in some very unusual ways. 

A cloud shadow being cast from Mount Rainier. Photo by Nick Lippert.
   One way is by an amazing cloud shadow that only occurs with several factors happening concurrently. At the approach of winter, when the Sun rises farther to the south, it is possible for the first rays of light at sunrise to pass through a dip in the Cascade Range and catch the peak of Mount Ranier. If that sunrise is also accompanied by a cloud layer above the mountain, it will project a shadow onto the bottom of the cloud layer creating a spectacular cloud shadow. This could never happen in the Rockies because even though there are several peaks taller than Mount Ranier, none of them have the topographic prominence that is needed. And as the sun rises its light will scatter too much to cast a shadow behind it.

   Another strange yet beautiful cloud phenomenon that you can see near Mount Ranier is lenticular clouds. These are lens-shaped clouds that form at high altitude. Because of their smooth, saucer-like shape, lenticular clouds have been mistaken for UFOs. Lenticular clouds are formed when moist air travels vertically over the mountain and creates a standing wave pattern on the downwind side. Moisture condenses at the crest of the wave and evaporates at the wave trough, creating the characteristics lens shape. Even though the wind continues to move down the mountain, the lenticular cloud will remain stationary. Lenticular clouds can appear singly, or in clusters or stacks. Pilots will avoid lenticular clouds because of the dangerous wind shears that accompany them, but thrill-seeking hang gliders will use them to ride the wave for several kilometers.

A stacked lenticular cloud formation near Mount Ranier.
   At some point in the future Mount Ranier will give us the most-spectacular—yet terrifying—show of all: when it erupts. Even though Mount Ranier is quiet now and has been since the 1890s, geologists consider this stratovolcano to be episodically active, which means that it WILL erupt again at some point in the future. It’s for this reason, and the fact that Mount Ranier is located near a highly-populated area, that it was included as one of 16 “Decade Volcanoes” worthy of study in an attempt to reduce the severity of a future natural disasters. These Decade Volcanoes were studied as part of the United Nations International Decade for Natural Disaster Reduction during the 1990s.

Sunday, September 2, 2012

Brocken Specter

Brocken specter as seen from 
the Golden Gate Bridge.

I love travelling through the mountains. The way the light plays off the mist in beautiful and sometimes eerie ways amazes me. If you're lucky enough to be at the right place at the right time, you might experience a rare and seemingly supernatural optical phenomenon called Brocken specter, named after the highest peak in the Harz mountains in Germany. 
   German Folklore dating back to the 17th century says that on the night of April 30 each year, exactly six months after Halloween, witches and sorcerers gather on the Brocken and revel with their gods as they await the arrival of spring. Among mountain climbers there is a superstition that a person who sees a Brocken specter will someday die on the mountain; local climbers have been so startled by the sudden appearance of a Brocken specter that they fall to their death, not realizing they are seeing their own harmless shadow.
Brocken specter from the 
Tanzawa Mountains in Japan.
   The Brocken specter appears when the setting sun casts a shadow from directly behind a climber at a higher altitude onto a cloud or mist at a lower altitude. When the shadow is cast upon a mist the sunlight surrounding it enters the suspended water droplets in the air and reflect back to the observer via diffraction, creating a rainbow-colored halo around the shadow's head. This halo is called solar glory. 
   The Brocken specter may appear to be huge because the fog hampers your depth perception. Only one's own shadow, seen in a mist, can converge with the antisolar point and combine with the solar glory to create the Brocken specter. Therefore, if you are travelling in a group you can only see your own Brocken specter.
Brocken specter from the Pamir Mountains of Tajikistan.