Clear Air Turbulence, Scales of Meteorology, Application of Micro-Meteorology

CAT (Clear Air Turbulence)

The atmospheric turbulence creates discomfort, increase stress on the aircraft and reduces the efficiency of operation. There are mainly four types of principle conditions that lead to the better understanding of the turbulence i.e Thermal, Frictional, Frontal and that turbulence which is associated with the upper-level waves.

Thermal turbulence:

The thermal turbulence is produced by the vertical convection above the heated surface or by the advection of cold air over a warm surface and is accentuated in an air mass that already has an unstable lapse rate.

Frictional turbulence:

The frictional turbulence results from the flow that across the rough terrain. This effects often combine with the convection current when an irregular surface is heated or cooled unevenly.

Along the cold front, the wind is shift and lifting of warm air above the cold may cause the wind shear, that is, pronounced differences in the wind velocity in adjacent air streams. Warm air moving over a ground inversion layer, as in a valley at night, creates a thin zone of wind share that can be especially dangerous. Although turbulent conditions may have accompanying clouds as warning signs, they also disturb the clear air. Wave-induced turbulence (WIT) is also known as the clear air turbulence (CAT) is the common vicinity of a jet stream where both of the horizontal and the vertical shear are generated. Refinements in the techniques of the observation by the Doppler radar and the infrared detections of the water vapor assist detection of wind shear at the considerable distance.

Scale of meteorology

The meteorology has many types of the parameters which are measured in various types of units. According to the parameters used, some of these parameters have local range. Some of the parameters have the regional while others have the global scale also. Taking this into the consideration there are mainly three types of the scales which are used in the meteorology. They are described as follows:

1: Microscale meteorology:

This microscale meteorology is the smallest scale of the meteorology in which the parameters have the variation in the local range only. It has scale smaller than a city and limited to only a few square kilometers. The Coriolis force i.e the force which occur due to the rotation of the earth is usually neglected in this type of scale. It is restricted to the lowest 100m of the atmosphere while this layer is very much important because the plants and the animals used to live here. Many of the atmospheric transformation take place here. Evaporation, evapotranspiration,convection and frictional wind are micro scales in the measurement.

2: Mesoscale meteorology

Mesoscale meteorology is the medium scale of meteorology. The scale is equivalent to the size of the few hundreds of kilometers. The mesoscale meteorological parameters are studied by the means of the observing station placed at the interval of about 10 square km.

A study of the atmosphere persuades on a geographical stage between those employed in the micrometeorology and the synoptic meteorology. Examples of mesometeorology are the sea breeze, land breeze, mountain wind and valley wind thunderstorm.

3: Macroscale meteorology:

Macro scale meteorology is the global scale of the meteorology. Here, the influencing parameters are studied globally. It has the scale as big as the continent of the globe itself. The worldwide weather pressure and the global temperature etc. are of macro scale in nature. In a macro scale or network of the observing stations are placed at intervals of 20 square kilometers. Monsoon is the macro scale global phenomenon. Examples: a study of the large-scale processes in the atmosphere occurring over the substantial region of the earth surface and including the general circulation of the atmosphere itself. Some of the examples are trading, the wind, jet stream etc.

These three scales i.e micro, so and the macro meteorological are very much close to each other because heat, moisture, and energy within the atmosphere are transformed with the help of these three scale parameters.

Jet stream

A horizontal temperature gradient exists while moving from the north to south along a meridian because of the curvature of the earth allows for the more solar heating than at the poles. This creates a westerly geostrophic wind pattern to form in the mid-latitudes. It is so because the thermal wind causes an increase in wind velocity with the height, the westerly pattern increases in the intensity up until the tropopause, creating a strong wind current known as the jet stream. The northern and the southern hemispheres exhibit similar to the jet stream patterns in the mid-latitudes.

By using the same thermal wind argument, the strongest part of the jet stream should be in proximity where temperature gradients are the largest one. Due to the step up of the continents in the North America, largest temperature contrasts are observed on the east Coast of the North America (boundary between the Canadian cold air mass and the gulf stream/warmer Atlantic ) and the Eurasia ( boundary between the boreal winter monsoon/ Siberian cold air mass and the warm pacific). However, the strongest part of the boreal winter Northern Hemisphere jet is observed over the east coast of the North America and Eurasia as well. Since the stronger vertical shear promotes baroclinic instability, so the most rapid development of extratropical cyclones (so called bombs) is also observed along the coast of the north America and Eurasia.

Similar arguments can be applied to the southern hemisphere. The lack of the continents in the southern hemisphere should lead to a more constant jet with the longitude i.e, a more zonally symmetrical jet and that is indeed the case on the observation.

Applications of micrometeorology

Microclimatology is restricted in the depth to the lowest hundred meters of the atmosphere from the surface boundary layer is studied under the micro-scale. This implies that some of the urban scale phenomena are studied under the micrometeorology. The micro-scale phenomenon affects the plants, animals and humans. So, the knowledge of micrometeorology is, therefore, useful in the agriculture, hydrology, forestry and as well as in the public health to the cities. And many of the great transformation in the atmosphere take place in its lower boundary.

Application of micrometeorology in vegetated surface

The meteorological parameters like temperature, light, precipitation, relative humidity, atmospheric pressure and winds affect the plant's growth and the distribution. Evapotranspiration and the photosynthesis are dependent on these parameters. The distribution and the growth rates of the vegetated species reflect the climatic conditions and the vegetation, in turn, affects the forest on climate are the greatest in the area and they are roughly proportional to the density of coverage but the forest also mostly modify or effects the climate of the adjacent areas. Widespread removal changes in the species composition or the compassion to the other types of the lands use after the surface heat and water budgets and may affect the regional climate.

Temperature (average) within a forest (vegetated surface) is slightly lower than in adjacent open area. The greatest average difference is usually in the summary (it may be as much as 2-degree centigrade) and in the winter it is used to be only 0.06-degree centigrade. In a dense forest the upper canopy shades the ground and its acts as the primary absorbing surface during the day, then it retards the temperature of the soil. At night the canopy radiates the heat more rapidly than the ground which is slower to cool. The same principle holds true for the seasonal radiation. Depending upon the density of the vegetated area up to the 90% of the sunlight is intercepted.

The albedo of the planet surface aids the control of the leaf and the steam temperature. Precipitation of the vegetated surface areas differs from the heat within the adjacent areas. Rain gauze in open space within the forest indicates greater rainfall than outside the forest. Increased transpiration, as well as evaporation of water intercepted by the vegetation, reduces surpluses in the water budget. Similarly, the vegetation increases the infiltration and reduces the stream flow from a watershed.

Relative humidity is 3 to 10% higher within the forest then the other open area. Owing to the lower temperature, lighter air movements, and transpiration from the plants. Evaporation from the soil is reduced because of the higher humidity and if the ground is well covered with plant litter, it is reduced by ½ to 2/3 as compared to the evaporation from the soil in the open fields. Surface wind speed is markedly used to reduced by the trees. By resisting air movement, trees aid in reducing evaporation, lowering temperature and increasing relative humidity.

References:

Miller, Jr. G.T. Living in the Environment. Wadsworth Publication, 2003.

S.C., Santee. Environmental Science. India, New Center: New Center Book Agency (P) Ltd, 2004.

T., Richard. Environmental Science Towards a Sustainable Future. India: PHI (P) Ltd., 2008.

Lal, D.S. Climatology, Sharda Pustak Bhawan, Allahabad.(2010)