Mean sea level pressure

Mean sea level pressure is the pressure at sea level or the station pressure condensed to sea level assuming an isothermal layer at the station temperature. This is the pressure usually given in weather reports on radio, television, and newspapers. When barometers in the home are set to match the local weather reports, they measure pressure condensed to sea level, not the actual local atmospheric pressure. The reduction to sea level means that the usual range of fluctuations in pressure is the same for everyone. The pressures which are measured high pressure or low pressure do not depend on geographical location. This makes isobars on a weather map meaningful and useful tool. The altimeter setting in aviation, set either QNH or QFE, is another atmospheric pressure reduced to sea level, but the method of making this reduction differs slightly.

QNH barometric altimeter setting which will cause the altimeter to read airfield elevation when on the airfield. In ISA temperature conditions the altimeter will read altitude above mean sea level in the vicinity of the airfield.QFE barometric altimeter setting which will cause an altimeter to read zero when at the reference datum of a particular airfield. In ISA temperature conditions the altimeter will read height above the datum in the vicinity of the airfield.

Timbre

In music, timbre, also timber, is the quality of a musical note or sound that distinguishes dissimilar types of sound production or musical instruments. The physical characteristics of sound that mediate the observation of timbre include spectrum and envelope. Timbre is also known in psychoacoustics as sound quality or sound color. For example, timbre is what, with a little practice, people use to distinguish the saxophone from the trumpet in a jazz group, even if they are playing notes at the same pitch and amplitude. Timbre has been called the psycho acoustician’s multidimensional wastebasket category as it can denote many apparently dissimilar aspects of a sound.

Tone color is also often used as a synonym. People who experience synesthesia may see certain colors when they hear particular instruments. Helmholtz used the German Klangfarbe and Tyndall proposed its English translation, clangtint. But both terms were disapproved of by Alexander Ellis who also discredits register and color for their pre-existing English meanings.

Sinkhole

Sinkholes, also known as sinks, shakeholes or dolina, and cenotes, are formed by the collapse of cave roofs and are a feature of landscapes that are based on limestone bedrock. The result is a depression in the surface topography. This may range anywhere from a small, gentle earth-lined depression, to a large, cliff-lined chasm. Most often there is a small area of rock exposure near or at the bottom of a sinkhole, and a patent opening into the cave below may or may not be visible. In the case of exceptionally large sinkholes, such as Cedar Sink at Mammoth Cave National Park, there may actually be a stream or river flowing into the bottom of the sink from one side and out the other side.

Sinkholes often form in low areas where they form drainage outlets for a closed local surface drainage basin. They may also form in currently high and dry locations. Florida has been known for having frequent sinkholes, especially in the central part of the state.

Earth

Earth whose Latin name is Tellus is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. It is also the largest of its planetary system's terrestrial planets, making it the largest solid body in the solar system, and it is the only place in the universe known to support life. The Earth was formed around 4.57 billion years ago and its largest natural satellite, the Moon, was orbiting it shortly thereafter, around 4.533 billion years ago.

Since it formed, the Earth has changed through geological and biological processes that have hidden traces of the original conditions. The outer surface is divided into several tectonic plates that gradually migrate across the surface over geologic time spans. The interior of the planet remains active, with a thick layer of convecting yet solid Earth mantle and an iron core that generates a magnetic field. The atmospheric conditions have been significantly altered by the presence of life forms, which create an ecological balance that modifies the surface conditions. About 71% of the surface is covered in salt water oceans, and the remainder consists of continents and islands.