Cuestionario global change and the climate system

UNIVERSIDAD
DE GUANAJUATO

Daniel Martínez Aldavera
Global Change & Climate Systems

DEFINE THE FOLLOWING TERMS

1. Firn

Snow or firn Firn is partially-compacted snow, a type of snow left over from past seasons and has been recrystallized into a substance denser than fresh snow. It is ice that is in an intermediate state between snow and glacialice. Firn has the appearance of wet sugar, has a hardness that makes it very difficult to work with a shovel. Overall density greater than 550 kg / m³ and is often found beneath the snow that accumulates at the head of a glacier.

Snowflakes are compressed under the weight of the mass of snow covering them. Individual crystals have a temperature close to melting are slurry, allowing them to glide alongcrystal planes and fill the spaces between them, thereby increasing the density of ice. Where the crystals touch they stuck together, pushing the air toward the surface or into bubbles.

During the summer months, the metamorphosis of the crystals can occur more rapidly because of water percolation between the crystals. Towards the end of summer, the result is firn.

References:
USGS Glossary ofSelected Glacier and Related Terminology
Fundamentals of Physical Geography

2. Geostrophic wind
It is a wind that is the balance between Coriolis forces and pressure gradient. A parcel of air initially is still high pressure moves downward because of the pressure gradient force. However, when that air parcel begins to move, is diverted by the Coriolis force in the right hemisphere (left inthe southern hemisphere), see Figure.

Figure. Balance between Coriolis force and pressure gradient
Source: University of Illinois

The Figure 1.17 illustrates this process, in which is shown in equilibrium the two forces that produce the geostrophic wind. The winds are geostrophic nature rarely, but with a good approximation, in the upper troposphere are very close to that status. Geostrophic areconsidered only when the isobars are straight and there is no other force acting, these conditions are not often found in nature.

Figure 1-17. Balance of forces produced by the geostrophic wind (northern hemisphere)
Source: Environmental Protection Agency U.S. – EPA
Source:
www.ideam.gov.co/.../AtlasAnexo1.html

3. Instrumental record
Instrumental Records 

Records that are used to studyand analyze using the common elements by instrumental records of climate such as temperature, precipitation (rain, snow and hail), humidity, wind, solar radiation and atmospheric pressure. According to internationally recognized procedures, measuring instruments must be properly installed in suitable locations, carefully maintained and seen to care. Even though it is not possible to measure theweather, the elements of climate records can be used to specify the physical state of the climate in a particular place during a period of time. These records of weather elements collected in the time known as "time series". 

The element most commonly measured is temperature. The temperature is a valuable element in the climate of climate observation, as it provides a direct measure of the energycontained in the controlled system. For example, global average temperatures reveals details of the energy content of Earth's climate system, and more significantly the overall energy balance. Changes in global temperature indicate changes in the overall energy balance. 

Many records of surface air temperature back to the mid-19th century. The oldest record comes from central England, and morethan 300 years. Measuring the air temperature is essentially the same now as then, the use of mercury in glass thermometers, which can be used down to -39 ° C, the freezing point of mercury. For lower temperatures, mercury is often a substitute for alcohol. More recently, observations of the temperature of the ocean surface were collected to provide a more accurate picture of the average global...