Precipitation

Introduction

  • Landscape and climate-ecosystem dynamics heavily influenced by precipitation.

  • Importance of latent heat and water vapor content in the atmosphere.

Observed Distribution of Precipitation

  • Variability in precipitation distribution observed globally.

  • Influences include temperature, moisture availability, air pressure, wind patterns, and geographical features such as mountains (orography).

Generation of Precipitation

Lifting Processes

  • Convective Lifting: Warm air rises due to heating from the surface, leading to expansion and cooling (dry adiabatic cooling).

  • Orographic Lifting: Air forced upwards by terrain, cooling as it ascends.

  • Frontal Wedging: Warm air rises over cooler, denser air masses.

  • Convergence: Airflows meet, forcing the air upwards.

Lapse Rates

  • Refers to the temperature decrease with altitude.

  • Observed global mean lapse rate: approximately 6.5 °C/km.

  • Dry Adiabatic Lapse Rate (DALR): Temperature decreases by 10 °C for every 1000 m ascent (dry air).

  • Saturated (Wet) Adiabatic Lapse Rate (SALR): Lower than DALR due to latent heat release; typically around 5 °C/km.

Links to Global Circulation

  • The impact of global wind belts and the three-cell model on precipitation patterns.

  • Hadley cells bring rainfall to equatorial regions, while the polar high leads to dry conditions.

Seasonality

  • Seasonal changes in precipitation due to shifts in atmospheric circulation and temperature.

  • Example: Mediterranean areas exhibit summer droughts due to subtropical high pressure.

Precipitation Regimes

General Zones of Precipitation

  • Regions classified as: humid, semiarid, arid, etc.

  • Relationships observed between annual precipitation and latitude, altitude, and geographical features.

Specific Characteristics

  • Arctic & Polar Regions: Sparse precipitation across seasons.

  • Midlatitudes & Subpolar Regions: Ample precipitation with seasonal variation.

  • Tropics: Characterized by abundant rainfall year-round; high evaporation rates.

Energy Budget of Earth

Incoming and Outgoing Radiation

  • Balance between absorbed solar radiation and outgoing long-wave radiation.

  • Key components:

    • Incoming solar radiation -100 units

    • Reflected radiation -30 units

    • Long-wave radiation emitted by Earth -64 units

Atmospheric Density and Pressure Profiles

  • Density decreases with altitude; pressure drops correspondingly.

  • Most air is concentrated in the troposphere; pressure profile mainly decreases as altitude increases.

Conclusion

  • Understanding precipitation processes is crucial in predicting climate patterns.

  • Impact of local conditions, large scale atmospheric processes, and human activity on precipitation dynamics.