GI - Weather

Geographical Investigation

Collecting data

Recording sheet and maps

Maps show the location of physical features and human activities.

Maps can also be annotated with the locations of recorded data. Further data analysis and presentation can then be carried out after fieldwork has been done.

Look at how different ground surfaces (concrete or vegetated) and shade (from shelter, trees, buildings) affect the temperature.

Use of weather instruments to collect the weather data.

Maximum and minimum thermometer to measure the maximum and minimum temperatures

When temperature rises, the mercury expands, pushing the metal index along the tube. When temperature falls, the alcohol contracts and pulls the metal index along the tube.

For the Six’s thermometer (U-shape maximum and minimum thermometer), the temperatures are obtained by reading the values indicated at the bottom of the metal index (indicators).

Mean daily temperature = sum of hourly temperatures divided by 24 hours

Diurnal temperature range = maximum temperature minus minimum temperature

Precautions to take when using thermometer

Rain Gauge to measure the rainfall

The amount of precipitation is measured in millimetres using a rain gauge. A simple rain gauge can be made using a funnel and a jar or tin. To determine the amount of precipitation:

1. Find an appropriate spot to place your rain gauge and position the rain gauge in an open area. It should be placed in an open area where there are no obstructions to block the rain and also avoid concrete surfaces as splashing may occur leading to an inaccurate reading.

2. Place the rain gauge into the ground with about 30 cm protruding above ground.

3. Record the time at which the rainfall events start and end.

4. Pour the collected water in the rain gauge into a measuring cylinder every 24 hours. Read and record the water level.

Precautions to take when using rain gauge

Put rain gauge in an open area so that there is no obstruction to the collection of water.
Put rain gauge away from trees / buildings so that water from the leaves of the tress / the building cannot drip into the rain gauge and make the measurement inaccurate
Rain gauge must be 30cm above ground level So that water from the ground cannot splash back into the rain gauge
Rain gauge must be partially sunk in the ground so that it is stable and when wind blows, it won’t topple.

Sling Psychrometer to measure relative humidity

RH measured using a sling psychrometer which also consists of a wet bulb thermometer and a dry bulb thermometer.

1. Dip the wick of the wet bulb in water and swing the psychrometer for 1 min. Remember to keep your elbow straighten and swing it above the head.

2. Record the reading. Repeat step 1 until both readings are consistent.

Hygrometer (Wet and dry bulb thermometer) to measure relative humidity

Relative humidity can be measured using a hygrometer at a weather station.

1. Read and record the temperature on the dry bulb thermometer.

2. Refer to the relative humidity chart.

3. Read the temperature of the dry bulb thermometer on the left column. The depression of the wet bulb is the difference between the wet bulb thermometer and the dry bulb temperature.

4. Find the value at which the dry bulb temperature intersects with the depression of the wet bulb.

You may find the maximum and minimum thermometer and the hygrometer housed in a Stevenson screen in a weather station

Why are the thermometers kept in the Stevenson Screen?

- Keeps out direct sunlight
- Elevated at least 1.5m above the ground as the ground can radiate heat which results in inaccurate readings
- Painted white to reflects heat thus not affected by the Sun’s direct heat
- Louvred sides allow free ventilation of air

Barometer to measure air pressure

Read from where measuring hand is pointing which shows the current air pressure.

Precautions to take when using the barometer:

● The students ensure that they do not place the barometer under direct sunlight to ensure we measure air temperature not solar radiation

● They must also not hold it too near their body or warmed object so that the body/ heated surface does not interfere with the measurement.

● The atmospheric pressure should be recorded at the same time throughout the fieldwork to ensure accuracy as atmospheric pressure varies throughout the day with the change in temperature.

Try out this exercise on the use of a barometer. Enter the readings on the barometer - Setting hand (movable pointer) is in blue and the Measuring hand is in red.

Then indicate whether it shows that the atmospheric pressure is increasing or decreasing.

Source: http://www.ontrack-media.net/gateway/science8/g_s8m0l7s6.html

A barometer has two hands. The hand on the inside is called the measuring hand. The hand on the outside directly over the measuring hand is called the movable pointer.

The moveable pointer is arranged over the measuring hand to mark the current pressure. The measuring hand will move according to the air pressure. The pressure is falling if the measuring hand moves to the left, and rising if the measuring hand moves to the right.

The dial expresses mercury in measurements in millibars (Mb).

Places with high temperature will experience low pressure. Places with low temperature will experience high pressure.

A greater difference in temperatures or air pressure between two places will result in higher wind speed.

Wind vane to measure wind direction

Wind direction refers to the direction that the wind is blowing from.

It is shown by a freely moving pointer on a wind vane. The wind vane is usually placed on a high, open place with little or no obstruction to the flow of wind. The direction the wind vane is pointing to is the direction where the wind is blowing from.

Anemometer to measure wind speed

An anemometer is used to measure wind speed and direction. It includes 3 to 4 cups mounted on a vertical pole. The cups catch the blowing wind and turn the pole. Each time the anemometer makes a full rotation, the wind speed is measured by the number of revolutions per minute (RPM). The number of revolutions is recorded over time and an average is determined.

Cloud cover

Cloud cover symbols indicate the amount of solar radiation that reaches the earth’s surface.

Places with more cloud cover will experience a smaller diurnal temperature range.

Temperatures will be lower in the day and higher in the night when there is more cloud cover.

Weather Tracker

The weather tracker can also be used to measure temperature other than atmospheric pressure, relative humidity and wind speed.

The weather tracker must be held at arms length, away from the body as body heat may affect the reading.

Make sure the cover is opened for the impeller to turn to measure wind speed.

Precautions to take when using weather tracker

What are the advantages and disadvantages of using a weather tracker compared to a analogue thermometer?

· Advantage: quick to read the readings/more accurate as reading given to the nearest 1 decimal place for temperature/ avoid student error such as parallex error in reading

· Disadvantage: Weak battery might not allow the weather tracker to work properly and give inaccurate reading

How can the measurements be improved to increase reliability?

The students should standardize the weather instruments used so that the results are comparable / to ensure a fair test.
They should also record the weather data at the same time of the day to ensure greater consistency in the data and for comparable results.
They should record a few more readings and calculate the average of the readings so that the data is more representative.

How can the data be represented graphically?

Wind rose

The rectangles point in the direction where wind is blowing from.
In the diagram below, there are more winds recording blowing from the Northeast. Thus the prevailing wind is from the Northeast.
The numbers represent the dates in a month in which the wind blew from a particular direction
The number in the middle shows the number of calm days. As shown in the diagram below there are 3 calm days which no wind is recorded.

The temperature and relative humidity readings are presented in the comparative line graph and scatter graph below.

Does the data representation prove that the hypothesis "When temperature increases, relative humidity decreases?" is true?
What type of relationship is shown in the data represented graphically?
Support your conclusion to the hypothesis with evidence from the data shown.

Take note of the following when drawing a comparative line graph:

Plot the independent variable which is time of the day on the X axis.
As this is a comparative line graph, it will have 2 dependent variables, one on the right Y axis and another on the left Y axis.
Label both X axis and Y axes.
Remember to also give a title for your graph.
Plot the points on the graph and join them to form the lines.
Do have a legend to show what the lines represent.

As seen from the graph, as temperature rises from 30 degree celsius to 33 degree celsius from 9.10am to 9.30am, the relative humidity decreased from 75% to 60%.

There is a negative correlation between temperature and relative humidity. As temperature increases, relative humidity decreases. As temperature decreases, relative humidity increases.

The best fit line (in red) on the scatter graph above is downward sloping indicating a negative correlation.

As temperature increases, relative humidity decreases.

Take note of the following when drawing a scatter graph:

Plot the independent variable which is temperature on the X axis.
Plot the dependent variable on the Y axis.
Label both X axis and Y axis.
Remember to also give a title for your graph.
Plot the points on the graph - DO NOT connect the points.
Draw a best fit line to show the general trend. The best fit line would have almost equal points on both side of it.

Concluding the hypothesis

Is the hypothesis proven true/false/Partially true?

Use the data to support your conclusion.

Are there any anomalies? Anomaly is data that is inconsistent with the trend. Could it be due to the current events or poor fieldwork techniques?

Are the data collected reliable? Are there ways to improve on the data collection?

Geohunt integrating weather GI using QR codes, Google form and Google sheets in 2018

https://geogshare.blogspot.com/2018/05/geohunt_12.html?m=1