Sound Propagation


Sound propagates through air as a longitudinal wave. The speed of sound is determined by the properties of the air, and not by the frequency or amplitude of the sound. Sound waves, as well as most other types of waves, can be described in terms of the following basic wave phenomena.

THE STORM IS OVER: A coronal mass ejection hit Earth on Dec. 16th, but the glancing impact failed to re-energize geomagnetic activity. The severe magnetic storm of Dec. 14th is truly finished.

GOODBYE... and thanks for the X-flares. Sunspot 930 announced itself on Dec. 5th with one of the strongest flares in years--an X9, followed by an X6 on Dec. 6th, an X3 on Dec. 13th and an X1 on Dec. 14th. Not bad for solar minimum!
Now the spot is departing. The sun's rotation is carrying it toward the western limb where it disappear from view in a day or so.

As soon as sunspot 930 is out of sight, solar activity will return to low levels. Stay tuned for quiet.

SOLAR TSUNAMI: When sunspot 930 exploded on Dec. 6th, producing an X6-category flare, it also created a tsunami-like shock wave that rolled across the face of the sun, wiping out filaments and other structures in its path. An H-alpha telescope in New Mexico operated by the National Solar Observatory (NSO) recorded the action:

"These large scale blast waves occur infrequently, however, are very powerful," says Dr. K. S. Balasubramaniam of the National Solar Observatory. "They quickly propagate in a matter of minutes covering the whole sun and apparently sweeping away filamentary material." Researchers are unsure whether the filaments were blown off or were compressed so they were temporarily invisible. Get the full story from the NSO.

Current Sun View of the EarthThe current position of the Sun over the Earth is a primary factor determining current radio propagation conditions between points on Earth, because energy from the Sun ionizes the ionosphere. Just as the part of the Earth the Sun is directly over tends to receive the most heat, it also tends to receive the most ionizing energy.
Current Solar High-Noon This is how the Earth would appear through a telescope from the Sun right now if the clouds currently around the Earth were removed. The Sun was directly over the point on Earth that is in the exact center of this image at the time it loaded in your web browser. The current gray-line transition between daylight and darkness extends around the extreme periphery of this globe. (Allow a few seconds for current-position calculations, image creation, and image loading.)

Current Moon View of the EarthThe current position of the Moon over the Earth is important to Earth-Moon-Earth (EME) moon-bounce communications, because two or more stations on Earth must be able to see the moon simultaneously to communicate.
Current View of Earth from the Moon This is how the Earth would appear through a telescope from the Moon right now if the clouds currently around the Earth were removed. The Moon was directly over the point on Earth that is in the exact center of this image at the time it loaded in your browser. (Allow a few seconds for current-position calculations, image creation, and image loading.)

The maximum usable frequency for any time through a 24-hour period can be determined by examining the green line. The frequency required to reach the receiver must exceed the frequency indicated by the red line or the signal will be reflected by the E-layer and will be more heavily absorbed. The optimum working frequency (or FOT) is indicated by the yellow line and is defined as the frequency corresponding to 85% of the MUF. Frequencies between the magenta colored line and the yellow line are often the best frequencies (most reliable) to use for the given transmitter and receiver.