Weather is the condition of the atmosphere at a specific time and place, including temperature, precipitation, wind, sunlight, humidity, and air pressure. Collecting weather data is crucial for understanding daily conditions, predicting future patterns, studying climate trends, and aiding industries like farming and transportation, as well as tracking severe events. Various instruments are used: thermometers for temperature, rain gauges for rainfall, anemometers for wind speed, wind vanes for wind direction, hygrometers for humidity, barometers for air pressure, and sunshine recorders for sunlight duration. Weather is observed and recorded regularly at stations using instruments and visual assessments, with data sent to central centers. Weather maps use symbols and colors to display this data, requiring understanding for interpretation. Weather forecasting is vital for safety during extreme events and supports many economic sectors. This topic introduces weather basics, the significance of its recording, measurement tools, observation methods, and the importance of weather maps and forecasts, highlighting a scientific approach to understanding and predicting the atmosphere.
Discuss
How are dew drops beneficial for plants ?
Ans:
Providing extra water through leaves, especially in dry areas.
Reducing water loss from leaves by slowing evaporation.
Offering a cooling effect in hot weather.
Slightly increasing soil moisture when it drips down.
Making some leaf nutrients available.
EXERCISES
A. Answer the following questions in brief
Question 1.
What is relative humidity? How does it differ from absolute humidity ?
Ans:
Relative Humidity (RH):
What: Percentage showing how full the air is with water vapor compared to its maximum capacity at the current temperature.
Feels Like: More relevant to how humid the air feels to us.
Temperature Sensitive: Changes with temperature even if the actual water vapor amount stays the same.
| Feature | Relative Humidity | Absolute Humidity |
| Definition | Ratio of actual to maximum water vapor at a given temperature. | Actual mass of water vapor per unit volume of air. |
| Units | Percentage (%) | g/m³ or kg/kg |
| Temperature Dependence | Highly dependent on temperature. | Independent of temperature (for a fixed air mass). |
| Indication | How close the air is to saturation. | The actual amount of water vapor present. |
| Relevance to Comfort | More directly related to how humid it feels. | Less directly related to how humid it feels. |
Question 2.
What does a large difference between the temperatures of a dry bulb thermometer and a wet bulb thermometer of a hygrometer indicate?
Ans:
A significant difference in temperature readings between the dry bulb and wet bulb thermometers of a hygrometer strongly suggests low relative humidity.
Here’s a breakdown in simpler terms:
Imagine the wet bulb thermometer has a damp cloth around it. As air moves past, the water evaporates, which has a cooling effect.
- Dry Air = Lots of Evaporation = Cold Wet Bulb: If the air is dry, it can soak up a lot of moisture. This makes the water on the wet bulb evaporate quickly, cooling it down significantly. The dry bulb, measuring the actual air temperature, will then show a much higher reading.
- Humid Air = Little Evaporation = Wet Bulb Closer to Dry Bulb: If the air is already full of moisture (high humidity), the water on the wet bulb won’t evaporate much. Therefore, the wet bulb’s temperature won’t drop much and will stay closer to the dry bulb’s reading
Question 3.
Differentiate between precipitation and condensation. Give one example of each.
Ans:
Condensation: Water vapor (gas) turning into liquid water, usually due to cooling. Example: Dew forming on grass.
Precipitation: Any water falling from clouds to the ground (rain, snow, sleet, hail). Example: Rain falling from clouds.
Question 4.
What are nimbus clouds?
Ans:
imbus clouds are, in simple terms, rain-bearing clouds.
There are two main types of nimbus clouds:
- Nimbostratus (Ns): These are dark, grey, featureless sheet-like clouds that often cover the entire sky. They are usually thick enough to block out the sun completely and have a diffuse base due to the falling precipitation.
- Cumulonimbus (Cb): These are large, towering, and often dark vertical clouds that are associated with heavy precipitation, thunderstorms, lightning, thunder, and sometimes hail or even tornadoes. They have a characteristic anvil-shaped top and can extend through all levels of the atmosphere. The “nimbus” part of their name indicates their ability to produce precipitation, while “cumulo” refers to their heaped or piled-up appearance.
Question 5.
What is the Beaufort scale?
Ans:
The Beaufort scale is a system created by Sir Francis Beaufort in 1805 to estimate wind strength based on observable effects, initially at sea and later adapted for land. It’s an empirical scale, meaning it relies on observation rather than precise measurements.
The scale assigns numbers from 0 to 12 (and sometimes higher for hurricanes) to describe wind force, with each number corresponding to specific visual cues like wave size at sea or the movement of trees on land. While it started as an observational tool, it was later correlated with approximate wind speeds in knots, mph, and km/h.
Although modern instruments are now common, the Beaufort scale remains useful for:
- Providing a general way to describe wind conditions.
- Offering a common language in marine forecasts.
- Estimating wind strength when instruments aren’t available.
B. Answer the following questions in one or two paragraphs
Question 1.
What is a hygrometer ?
Ans:
Instead of directly measuring the water content, most hygrometers work by sensing changes in a material or electrical property that occur as it absorbs moisture from the surrounding air. These changes are then converted into a reading that indicates the level of humidity. Different types of hygrometers use various methods to achieve this measurement.
Question 2.
Describe the various types of clouds.
Ans:
Clouds are categorized by height and look:
- High (icy): Wispy Cirrus, rippled Cirrocumulus, sheet-like Cirrostratus (halo effect).
- Mid (mixed): Puffy patches Altocumulus, gray sheets Altostratus (dim sun/moon), steady rain Nimbostratus (dark, featureless).
- Low (water): Uniform gray Stratus (drizzle), lumpy layers Stratocumulus, puffy, fair-weather Cumulus.
- Vertical: Towering storm clouds Cumulonimbus (heavy rain, storms), tall Cumulus Congestus (can become storms).
Question 3.
What is wind? What precautions must be taken while placing a wind vane?
Ans:
What Wind Is:
Wind is simply air in motion. This happens because the sun heats different parts of the Earth unevenly, causing air pressure differences. Safe Wind Vane Placement:
To get correct wind direction readings, be careful where you put a wind vane:
- Go High: Put it as tall as you can, at least 30 feet up and on flat ground, to avoid things on the ground messing with the wind.
- Away from Stuff: Keep it at least twice as far away as tall buildings or trees. These can make the wind swirl and give wrong readings.
- Open Space: Pick a spot where wind can blow freely from all sides without being blocked or changed. Don’t put it in dips in the land, near lots of trees, or between close buildings.
- Strong Base: Make sure it’s attached firmly and straight up on a steady pole so it doesn’t wobble and give bad readings.
- Even Parts: Check that the arrow and tail are balanced as the maker says. This lets it spin easily and point the right way.
- Check Alignment: If needed, set it up so it points correctly to North, South, East, and West using the maker’s instructions.
- Keep it Clean: Look at it now and then to make sure it spins freely and nothing like nests or dirt is in the way.
- No Interference: If it has electric parts, keep it away from things that can cause electrical or magnetic problems.
Question 4.
What are isohyets and isotherms ?
Ans:
Lines on geographical maps that connect locations with identical amounts of total precipitation recorded over a specific time frame are called isohyets.
Similarly, lines on geographical maps that connect locations experiencing the same temperature at a particular moment or sharing the same average temperature across a defined period are known as isotherms.
To put it simply:
- Isohyets represent areas of equal rainfall.
- Isotherms represent areas of equal temperature.
Question 5.
What is a weather report ? How is weather forecast made? Why is weather forecast necessary ?
Ans:
A weather report is a description of the current atmospheric conditions at a specific location and time, based on direct measurements. It details elements like the present temperature, air moisture, wind speed and direction, any precipitation occurring, cloud cover, and the pressure of the atmosphere.
A weather forecast is a scientific prediction of future atmospheric conditions for a particular area. It’s created through a detailed process:
- Gathering Data: Meteorologists collect vast amounts of information from ground stations, weather balloons, satellites, radar, ships, and aircraft globally, measuring temperature, pressure, wind, humidity, precipitation, and clouds.
- Analyzing Information: This data is sent to weather centers, where it’s processed, analyzed, and displayed on maps. Experts interpret this information to understand current weather patterns like pressure systems and fronts.
- Using Computer Models: Powerful computers run complex programs that simulate the atmosphere’s behavior using current data and physical laws to predict future conditions.
- Expert Refinement: Meteorologists review the computer model outputs, considering their strengths and local geographical factors (like mountains and coasts), to improve the accuracy of the forecasts.
- Sharing the Forecast: The final forecast is communicated to the public through television, radio, the internet, and apps.
Weather forecasts are essential because:
- Safety: They give vital warnings for dangerous weather like storms, heat waves, and blizzards, allowing people to protect themselves and their property.
- Daily Planning: People use forecasts to plan their daily activities, like what to wear and whether outdoor events are feasible.
- Economic Support: Many industries rely on accurate forecasts:
- Farming: For planting, harvesting, and protecting crops.
- Aviation and Shipping: For safe travel routes and operations.
- Construction: For scheduling work and ensuring safety.
- Energy: For predicting demand for heating and cooling.
- Tourism: For travel plans and outdoor activities.
- Emergency Response: They help emergency services and governments prepare for and manage severe weather impacts.
- Resource Management: They aid in managing water supplies, predicting floods, and planning for droughts.
C. For a week, gather information on the weather conditions of your city using simple instruments or from weather reports published in newspapers. Present this information in a table. One has been done for you here. My observation of the weather at for a week.
D. This could be a classroom activity. If your school laboratory has an anemometer, use it to record your city’s wind speed for a week. Use the Beaufort Scale to find out the character of wind during these days. Record your observations carefully in your notebook. You could even draw small neat sketches to show the effect of the wind.
Ans:
Do it Yourself
E. From the weather report published in your local newspaper, record the time of sunrise and sunset for a month in your notebook, as shown on the next page : My observation of the time of sunrise and sunset for the month of ______ 20, ______.
Ans:
Do it Yourself
F. Picture Study
1. Identify the four types of clouds shown in the photographs.
Ans:
(a) Cirrus clouds
(b) Cumulus clouds
(c) Stratus clouds
(d) Nimbus clouds
2. Which of these causes heavy rainfall?
Ans:
Nimbus clouds causes heavy rainfalls.
