Introduction

Weather is the day-to-day state of the atmosphere and pertains to short-term changes in conditions of heat, moisture, and air movement. Aviation Weather fundamentally results from processes attempting to equalize differences in the distribution of net radiant energy received from the sun. On the other hand, the processes of exchange of energy and mass between the earth and the atmosphere over a long period of time result in the conditions known as climate. It is more than a statistical average. Climate is the aggregate of atmospheric conditions involving heat, moisture, and air movement. It is an important element of the physical environment of mankind. The term originated from the Greek words “Klima” (referring to the supposed slope of the earth and approximating the concept of latitude) and “Logos” (a discussion or study). Climatology is closely allied with Meteorology, which treats day-to-day atmospheric conditions and their causes.

Definition of Weather and Climeteorology

 Weather is taken to mean the totality of the atmospheric conditions at any particular place and time, in which the instantaneous state of the atmosphere, especially those elements of it having a direct bearing on living things, is considered. Climatology is the study of climate, the long-term aspects, and total effects of meteorological processes. It is, in fact, a branch of earth physics. It deals with the various conditions of the atmospheric condition that occur and everything that habitually or occasionally influences the conditions of the atmosphere, either locally or over a great region of the earth. It is like any other branch of physics concerned with measuring the effects of some influence and seeking to discover the laws or principles of general application governing their behaviors and interactions.

Elements of Weather: The elements of weather are as follows:

a. Temperature

b. Atmospheric pressure

c. Wind

d. Cloud

e. Rain

f. Visibility

g. Humidity

Diurnal and Seasonal Changes of Weather: Before discussing the diurnal and seasonal changes of weather, one should know about the spells of weather. Spells of weather are the repetitive sequence of weather over several days or weeks at a place, known as spells of weather. Spells of weather are of two types:

a. Short Spells: These are expected to last for a few days (Suspended dust type wind, calm wind).

b. Long Spells: These last for several weeks (Monsoon, cold and heat wave). Diurnal changes are the changes that occur directly because of the changing radiation conditions as day follows night and night follows day. It is important to note that the diurnal change outside the tropics is not marked. Seasonal changes are recognized in the same way as the diurnal change, having characteristic larger time scales (Monsoon).

Change of Climate

These invariably involve the slowest and the longest-lasting, and probably the largest scale processes that meteorology is concerned with. They appear as changes in the average level of temperature in different parts of the world of the order of 2 to 12 degrees Celsius as between ice ages and warm interglacial times and changes from a fraction of a degree up to 2 to 4 degrees Celsius between various post-glacial periods of much shorter duration. Rainfall variations are also involved in certain cases, for instance, where the arid (dry) zone undergoes some displacement, where mild moisture veering wind penetrates further or less far into the polar region, or where the prevailing winds and the lee effects at a mountain barrier undergo a shift. The average rainfall may be multiplied many times or reduced to a small fraction of its former value.

Aviation Weather Reports

METAR

Understanding Aviation Weather Reports METAR, or Meteorological Aerodrome Report, is vital in aviation for providing timely weather information. Issued at hourly or half-hourly intervals, METAR reports follow a specific structure, encompassing various elements:a. Identification groups.b. Surface wind.c. Surface visibility.d. Runway Visual Range (if available).e. Present Weather.f. Cloud (or vertical visibility if appropriate).g. Temperature and dew point.h. QNH.j. Supplementary Information.

CAVOK

Clear Skies in Aviation Weather Reports CAVOK, an abbreviation for Ceiling And Visibility OK, indicates excellent weather conditions. It replaces visibility, present weather, and cloud groups under specific criteria:a. Visibility of 10 KM or more.b. Absence of clouds below 1500 meters (5000 feet) or below the highest minimum sector altitude, whichever is greater, with no cumulonimbus clouds.c. No significant weather phenomena.

Surface Wind Details

Surface wind is expressed through a five-figure group indicating wind direction and speed. Additionally, gusts and directional variations are reported.

Horizontal Visibility

Horizontal visibility is reported in meters, with directional variations noted when significant.

Runway Visual Range (RVR)

RVR, crucial for safe landing and takeoff, is reported for runway visibility, with exceptions for extreme values.

Cloud or Vertical Visibility Reporting

Cloud cover is coded, indicating the expected amount and height of clouds.

Cloud Type Identification

Significant convective clouds, like Cumulonimbus (CB) and Towering Cumulus (TCU), are identified in reports.

Reporting Cloud Groups

Cloud layers are reported based on specific criteria, with a limit on the number of groups.

Reporting Procedure for Clouds

Cloud reporting follows a structured procedure, ensuring accurate depiction based on height and type.

Additional Cloud Reporting InformationVarious considerations, such as reporting order and abbreviations, are observed for accurate cloud reporting.