lecture recording on 24 February 2025 at 18.36.32 PM

Hydrologic Cycle and Water Phases

• Water Phases:

  • Ice: Representing the frozen state of water (cryosphere).

  • Liquid Water: Standard state of water.

  • Water Vapor: Present in the atmosphere; significant in humid areas (e.g., offshore in summer).

Humidity and Weather

• Evaporation: More water evaporates over the ocean; clouds form, and when they move over land, they release precipitation.

• Humidity Discussion:

  • Climate around coastal areas can feel uncomfortable due to high humidity and elevated temperatures.

  • Impact of Humidity: Higher evaporation rates lead to more moisture in the air.

Water Movement and Direction

• Water Flow:

  • Water naturally moves downhill, following gravity.

  • Rivers in the US generally flow south, but some flow north (e.g., Red River).

• Precipitation: After precipitating, excess water flows to lower points.

Relative Humidity vs. Specific Humidity

• Measurements:

  • Relative humidity can be misleading, especially with temperature changes.

  • Specific Humidity: A more accurate measure of moisture content; expressed in grams per kilogram.

Effects of Temperature and Humidity on Comfort

• Heat Index: Higher humidity can make warm temperatures feel hotter than they are.

• Examples:

  • Southern summer humidity can feel oppressive.

  • Evaporation is a cooling process; this effect varies by location.

Dew Point and Comfort Levels

• Dew Point: The temperature at which air becomes saturated.

  • High dew points (e.g., 80°F) indicate uncomfortable humidity levels.

  • Daily average dew point in July can be around 71°F-72°F, indicating high humidity.

Seasonal Changes in Humidity

• Winter Humidity: Dew points drop; average in winter is about 40°F.

• Summer Conditions: Humidity dictates outdoor activity comfort levels; high humidity leads to discomfort and reluctance to be outside.

Regional Differences in Humidity

• Comparative Analysis:

  • In the Midwest (e.g., Ohio, Illinois), summer temperatures may be tolerable due to lower dew points.

  • Southern California has higher temperatures but low humidity; creates different comfort levels than humid locations like Alabama.

Coping with Humidity in Different Climates

• Adaptations:

  • Use of humidifiers in dry climates to maintain moisture levels indoors.

  • Swamp coolers effective in low-humidity areas but counterproductive in high-humidity areas.

Extreme Weather Conditions and Heat Index

• Instances of Extreme Heat: Areas with low humidity can reach very high temperatures without feeling as oppressive due to lack of moisture.

• Best Practices: Be mindful of dew points and humidity levels when planning outdoor activities, especially in summer.

Fog Formation

• Types of Fog:

  • Evaporation fog: occurs when warm, moist air moves over a cold surface.

  • Inversion fog: occurs when cold air is trapped near a surface, with warmer air above.

Conclusion

• Weather Awareness: Monitoring weather conditions, especially dew points, is critical for comfort and safety.

• Environmental Impacts: Understanding humidity's effects on temperature perception can help with personal comfort and outdoor activities.