Weather Data | Geography for GCSE/IGCSE - Year 11 PDF Download

Calculations using Weather Data

Rainfall

• Rainfall totals are recorded daily, weekly, monthly, and annually.
• Measurement is standardized in millimeters (mm).
• Data is typically visualized on a bar graph.
• Mean monthly and annual rainfall averages are calculated over at least 30 years.

Describing Annual Rainfall Amounts:

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Temperature

• Measured in °C or °F
• Always plotted as a line graph
• Calculations are:
  • Diurnal (daily)
  • Mean daily temperature
  • Mean monthly temperature
  • Annual range
  • Mean annual range

Describing Temperatures:
Describing Temperature Ranges:

Wind

• Temperature is measured in different units like Knots (Kts), Miles per hour (mph), and Kilometres per hour (km/h).
• Wind direction is indicated from where it is coming using compass points, providing insights into temperature and moisture levels.
• The prevailing wind, like the southwest wind in the UK, is the most common wind direction in a region.
• The dominant wind signifies the strongest wind direction in an area.
• Wind barbs are used to plot wind speed and direction on a map.

Describing Wind Speeds:

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Pressure

• Pressure is typically measured in millibars (mb) in relation to the average sea level pressure.
• The mean (average) sea level pressure is commonly at 1013mb.
• Pressure readings are time-dependent, varying based on specific circumstances:
  • Following a storm or potential storm, frequent pressure readings, sometimes hourly, are necessary.
  • Weekend forecasts generally entail daily pressure measurements.
  • For sailing forecasts, an initial morning reading may be required, followed by subsequent updates.
• Isobars on weather charts connect areas with equal sea-level pressures:
  • These isobars help identify atmospheric features like anticyclones (high pressure areas) and depressions (low pressure areas).
• Characteristics of high-pressure systems (anticyclones):
  • Winds in high-pressure areas are usually gentle and flow clockwise (in the northern hemisphere).
  • The descending air suppresses cloud formation, resulting in light winds and stable weather conditions.
• Features of low-pressure systems (depressions):
  • Air in low-pressure areas ascends and moves counterclockwise around the center (in the northern hemisphere).
  • As the rising air cools, water vapor condenses to form clouds and possibly precipitation.
  • Depressions often bring unsettled weather with associated weather fronts.
• High-pressure systems are termed as such even if they do not reach 1013mb, surrounded by lower pressures.
• Conversely, low-pressure areas can have central pressure exceeding 1013mb, enclosed by higher pressures.

Describing Pressure Systems:

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Relative Humidity

Relative humidity is a measure of the moisture content in the air in relation to the maximum amount of moisture that air can hold at a specific temperature.

• It is determined by observing where the depression of the wet bulb thermometer intersects with the dry bulb temperature line.
• Humidity is expressed as a percentage of the air's temperature.
• Temperature influences relative humidity; warmer air can hold more water vapor.
• For instance, at 20°C, air holding 4 grams of water has a relative humidity of 27%. If more water is added, the humidity increases until saturation is reached.
• When the temperature rises, air can hold more water, causing relative humidity to decrease. Conversely, as temperatures drop, excess water is released until equilibrium is achieved.