Understanding Meteorology: A Comprehensive Guide to Weather and Climate

Posted on May 7, 2024 in Geology

Branches of Meteorology

Descriptive Meteorology: Variables (ptvh)

This branch focuses on observing and describing atmospheric variables such as pressure, temperature, wind, and humidity.

Climatological Meteorology: Factors (cespf)

This branch studies the long-term patterns and trends of weather, including the factors that influence climate, such as latitude, altitude, and ocean currents.

Dynamic and Weather Forecast Meteorology: Phenomena

This branch deals with the physical processes that govern weather, including the formation of clouds, precipitation, and storms, and uses this understanding to predict future weather conditions.

The Atmosphere

The atmosphere is a gaseous layer surrounding the Earth, extending upwards for approximately 1000 km. It is divided into five distinct layers:

Layers of the Atmosphere Based on Temperature

1. Troposphere

  • Height: Approximately 13 km (variable thickness)
  • Contains most of the atmosphere’s water vapor
  • Temperature decreases with altitude
  • Location of most weather phenomena
  • Bounded by the tropopause, where the jet stream is found

2. Stratosphere

  • Height: 13-50 km
  • Temperature: -40°C to -3°C
  • Contains the ozone layer, which absorbs UV radiation and heats the air
  • Air is less dense than in the troposphere

3. Mesosphere

  • Height: 50-85 km
  • Temperature decreases with altitude, reaching a minimum of -90°C
  • Pressure is very low, around 1 hPa

4. Thermosphere

  • Temperature increases with altitude due to absorption of solar radiation
  • Height: 85-500 km

5. Exosphere

  • Height: 500-1000 km
  • Contained within the magnetosphere
  • Transition zone between Earth’s atmosphere and interplanetary space
  • Where artificial satellites orbit

Ionosphere

  • Region of the atmosphere with a high concentration of electrons and ions
  • Atoms are ionized by solar radiation
  • Extends up to 500 km
  • Divided into three layers: D (60-90 km), E (90-140 km), and F (140-210 km)

Weather Variables

Major Variables

  • Temperature
  • Density
  • Pressure
  • Water Vapor (H2O)

Minor Variables

  • Clouds
  • Precipitation
  • Winds

Weather vs. Climate

Weather refers to the atmospheric conditions at a specific time and place.

Climate refers to the long-term average of weather patterns in a region over an extended period.

Atmospheric Pressure

Pressure is the force exerted per unit area. In the context of the atmosphere, it is the weight of the air column above a given point on the Earth’s surface.

  • Pressure decreases with altitude at a rate of approximately 1 hPa per 9 meters.
  • Measurement: Since the 17th century, mercury and aneroid barometers have been used to measure atmospheric pressure. In nautical meteorology, three corrections are applied to barometer readings: instrumental, temperature, and gravity.
  • Units: The standard unit of pressure in atmospheric physics is the Pascal (Pa). Other commonly used units include millibars (mb), hectopascals (hPa), and atmospheres (atm). 1 mb = 1 hPa; 1 atm = 101,325 Pa = 1,013 hPa

Pressure Concepts

  • Pressure Tide: Regular daily variations in atmospheric pressure.
  • Instability: Irregular variations in the pressure curve.
  • Barometric Tendency: The change in pressure between two observations.
  • Isobars: Lines connecting points of equal pressure on a weather map.
  • Isallobars: Lines connecting points of equal pressure tendency.
  • Isohypses: Lines connecting points of equal geopotential height (height above sea level where the pressure is the same).
  • Gradient: The difference in pressure per unit distance.
  • Buys-Ballot’s Law: In the Northern Hemisphere, if you stand with your back to the wind, low pressure will be to your left and high pressure to your right.

Isobaric Forms

Isobars on a weather map can take various shapes, representing different pressure patterns:

  • Highs and Lows: Areas of high and low pressure, respectively.
  • Ridge: An elongated area of high pressure.
  • Trough: An elongated area of low pressure.
  • Col: A saddle point between two highs and two lows.

Pressure and Altitude

Pressure decreases with altitude. Here are some approximate pressure values at different altitudes:

  • 850 hPa: 1500 meters
  • 700 hPa: 3000 meters
  • 500 hPa: 5500 meters
  • 300 hPa: 9000 meters
  • 250 hPa: 10,300 meters
  • 200 hPa: 11,800 meters

Temperature

Temperature is a physical property that represents the degree of hotness or coldness of a body. It is a measure of the average kinetic energy of the molecules in a substance.

  • Measurement: Temperature is typically measured using a thermometer, which relies on the expansion of a liquid (usually mercury) with increasing temperature.
  • Units: Several temperature scales are used, including Celsius (°C), Fahrenheit (°F), Kelvin (K), and Rankine (R).

Temperature in the Atmosphere

The sun is the primary source of heat for the Earth’s atmosphere. Solar radiation is transmitted through the atmosphere and absorbed by the Earth’s surface, which then radiates heat back into the atmosphere.

  • Daily Temperature Variation: The Earth’s surface experiences a daily cycle of heating and cooling, resulting in a characteristic temperature curve with a maximum around 2 pm and a minimum around 6 am.
  • Annual Temperature Variation: The Earth’s tilt and orbit around the sun cause seasonal variations in temperature.
  • Continentality: Land areas tend to experience greater temperature extremes than oceans due to the differences in their heat capacities.
  • Isotherms: Lines connecting points of equal temperature on a weather map.
  • Heat Equator: The line connecting points with the highest annual average temperature. It does not coincide with the geographic equator due to the uneven distribution of land and water masses.

Humidity

Humidity refers to the amount of water vapor present in the air.

  • Sources of Water Vapor: Oceans, seas, rivers, and lakes are the primary sources of water vapor in the atmosphere.
  • Evaporation: The process by which liquid water transforms into water vapor.
  • Condensation: The process by which water vapor transforms back into liquid water.
  • Factors Influencing Humidity: Temperature, wind speed, and the availability of water sources all affect humidity levels.

Humidity Indices

  • Vapor Pressure (e): The partial pressure exerted by water vapor in the air.
  • Saturation Vapor Pressure (es): The maximum vapor pressure possible at a given temperature.
  • Absolute Humidity (a): The mass of water vapor per unit volume of air.
  • Relative Humidity (h): The ratio of the actual vapor pressure to the saturation vapor pressure, expressed as a percentage. It indicates how close the air is to saturation.
  • Dew Point: The temperature to which air must be cooled for water vapor to condense into liquid water.

Psychrometric Tables

Psychrometric tables or charts are used to determine various humidity parameters based on dry-bulb and wet-bulb temperature readings.

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