Contents
Biology Topics encompass a wide range of subjects, from cell biology to ecology.
Weather Conditions and Forecast by Locations
During the summer days, we wear light coloured clothes because the weather is hot. In winter, we prefer to wear dark coloured clothes because the weather is cold. And if there are clouds in the sky on a particular day, we usually take an umbrella (or raincoat) with us because the weather is cloudy and it may rain any time.
If there is going to be a religious function or a wedding in our family, then our elders discuss the weather which is likely to be at that point of time and plan accordingly (by putting up tents only or making a water-proof pandal). Many times we have heard the experts discussing weather on radio or television before the start of a game such as a cricket match. This is because, say, a cloudy weather can change the course of a cricket match or spoil it altogether by bringing showers of rain. Thus, weather has a great effect on our lives. In fact, many of our activities are planned by taking into account the weather predicted for that day. It is for this reason that there are daily reports of impending weather (coming weather) in newspapers, radio and television.
If, however, we are planning to go to a hill station for holidays, then we always take along woollen clothes with us because the climate on the hill stations is always cold. On the other hand, if we are going to a coastal area (sea-side area), then we do not need woollen clothes because the climate there is not cold. As we will study after a while, weather and climate are two different things. In this Chapter, we will first discuss weather and climate, and then describe how different types of animals are adapted to the climates of their habitats. Before we do that, we should know the meaning of the terms ‘humidity and ‘rain gauge’. These are discussed below.
We know that air (or atmosphere) always contains some water vapour (or moisture) in it. Humidity is a measure of water vapour (or moisture) in air. When the amount of water vapour in the air is high, we say humidity is high and the air feels moist (or damp). Under these conditions, the sweat (pasina) from our body does not evaporate readily and we feel hot and uncomfortable. If the humidity in an area is generally high, the climate there is said to be humid. On the other hand, if the amount of water vapour in the air is low, we say the humidity is low. When the humidity is low, the air feels dry.
Under these conditions, the sweat from our body evaporates readily and we feel cool and comfortable. Humidity of air is expressed as a percentage (%). A humidity of 100 per cent (100%) at a particular temperature means that the air is saturated with water vapour at that temperature (which means the air is holding the maximum amount of water vapour for that temperature). A humidity of 50 per cent (50%) means that the air contains half the amount of water vapour required for saturation at that temperature. Rainfall is measured by an instrument called ‘rain gauge’. Rain gauge is basically a measuring cylinder with a funnel at the top to collect rainwater. Rain gauge measures the rainfall at a place in the unit of‘millimetres’ (mm).
If the temperature of air (or atmosphere) around us on a particular day is high, we say that the weather is ‘hot’ today. If the temperature on a day is low, we say that the weather is ‘cold’. If there is lot of water vapour (or moisture) in the air, we say that the weather is too ‘humid’. If there is rain, we say the weather is ‘rainy’ today (see Figure). And if a lot of wind starts blowing on a day, then we say that the weather is very ‘windy’ today. So, when we talk of weather, we are actually describing the condition of the atmosphere (or air) around us at a particular time. We can now define weather as follows : The day-to-day condition of the atmosphere at a place and time with respect to the temperature, pressure, humidity, wind speed and wind direction, sunshine, clouds, rainfall (or snowfall), etc., is called weather at that place at that time. The various factors which decide weather at a place are called ‘elements’ of weather.
The major elements of weather at a place are temperature, pressure, humidity, wind speed and wind direction, sunshine, clouds, and rainfall (or snowfall). Weather is called ‘mausam’ in Hindi.
There are many different types of weather. Some types of weather are: hot, cold, sunny, cloudy, foggy, dry, humid, windy and rainy. The weather at a place is generally not the same on any two days. The weather at a place changes day after day and week after week. Actually, weather is such a complex phenomenon that it can change even over very short periods of time.
For example, it can be sunny weather in the morning but suddenly clouds may appear from nowhere and it can become cloudy. And if it starts raining, then it becomes rainy weather. It is also possible that a heavy rain may vanish in a matter of minutes and give way to bright sunshine. Weather is never constant anywhere. So, it is not easy to predict weather. The weather plays a big part in our lives today. Weather affects many of the things we do. For example, we wear the clothes according to the prevailing weather ; we eat food depending on weather; and we make our travel plans keeping the weather in mind. We will now discuss the source of weather and why weather changes so frequently.
What Produces Weather
Weather is produced by the heat of the sun and the effect it has on the atmosphere. This happens as follows: The sun is a huge sphere of hot gases at a very high temperature. Though the distance of the sun from the earth is very large, even then it is the source of all heat and light on the earth (see Figure). The heat energy of the sun absorbed and reflected by the earth’s surface, oceans and atmosphere, plays an important role in determining the weather at any place.
For example, the sun’s heat causes water from the oceans and land to evaporate. These water vapour rise high up in the atmosphere, get cooled, condense and form clouds in the atmosphere which produce rain leading to ‘rainy’ weather. Similarly, heat from the sun heats the earth’s surface. The hot surface of earth heats the air near it. This hot air (being lighter) rises up creating an area of low pressure. Air from high pressure area moves towards the low pressure area. The air moving from high pressure area to low pressure area is called wind. So, it is the sun’s heat which causes wind to blow and gives us ‘windy’ weather.
From the above discussion we conclude that the ‘rainy weather’ and ‘windy weather’ are produced by the sun. In fact, all types of weather (and all changes in weather) are caused by the sun. Thus, the sun is the primary source of energy which causes changes in the weather. The weather changes so frequently because the condition of the earth’s atmosphere keeps changing frequently due to the various effects produced by the sun’s heat.
Maximum and Minimum Temperatures
The ‘highest temperature’ reached during a day is called the ‘maximum temperature’ and the ‘lowest temperature’ during the day is called the ‘minimum temperature’.
In order to prepare weather reports, the maximum and minimum temperatures are recorded at a place every day. The maximum and minimum temperatures reached during a whole day are recorded automatically by a special thermometer called ‘Maximum-and-Minimum thermometer’ (see Figure). Please remember that :
- The maximum temperature of the day generally occurs in the afternoon, and
- The minimum temperature of the day generally occurs in the early morning.
During summers, we feel miserable in the afternoon because the maximum temperature of the day is reached in the afternoon (making the surroundings very hot and unbearable). On the other hand, we feel comparatively cool and comfortable in the early morning during summers because the minimum temperature of the day is reached in the early morning (making the surroundings somewhat cooler).
In any month of a year, all the seven days of the week do not have the same maximum and minimum temperatures at a place. The maximum and minimum temperatures keep on changing day by day. The maximum and minimum temperatures recorded at Delhi for a week from 01 November 2008 to 07 November, 2008 are given in the following table. A graph showing the variation of maximum temperature during this week is given in Figure.
By carefully monitoring the atmospheric conditions such as temperature, pressure, humidity, wind speed and wind direction, sunshine, cloud formations, rainfall (or snowfall), etc., it is possible to predict the coming weather in advance. Prediction of weather in advance is called weather forecasting. Weather experts use the various types of data collected by Earth Stations in different parts of the country as well as by the Satellites orbiting high up in the sky to predict weather (or forecast weather) well in advance. The scientific study of weather is called meteorology. The scientists who study and forecast weather are called meteorologists.
Weather Reports
We can see the daily weather reports in newspapers. The weather reports are also read on radio and shown on TV. The daily weather report carries information about the temperatures, humidity and rainfall during the past 24 hours. It also gives the timings of sunrise, sunset, moonrise and moonset. The weather report also predicts the weather for the day. A sample of the weather report which appeared in a newspaper on a Monday morning in the month of November 2008 in Delhi is given in Figure.
(i) The weather report given in Figure tells us that the maximum temperature during the past 24 hours was 33°C (The figure +3 in brackets means that this maximum temperature is 3°C above normal). The minimum temperature during the past 24 hours is shown to be 16°C (The figure +2 in brackets means that this minimum temperature is 2°C above normal).
(ii) The weather report tells us that the moon will set on Monday at 9.30 pm and moon will rise on Tuesday at 11.55 pm. It also informs us that the sun will set on Monday at 5.34 pm and the sun will rise on Tuesday at 6.36 am.
(iii) The forecast of weather for the day given in the weather report tells us that : Sky will remain clear (which means no clouds, etc.) but there will be mist in the morning. The maximum and minimum temperatures predicted for the day are around 33°C and 17°C respectively.
(iv) The weather report given in Figure also tells us that the maximum humidity recorded in the past 24 hours was 82 per cent and the minimum humidity was 29 per cent.
(v) Since rainfall does not occur every day, so no rainfall has been recorded in the above weather report during the past 24 hours.
Weather reports are prepared by the scientists (called meteorologists) of the Meteorology Department of the Government. Meteorological Department collects all the data on the condition of atmosphere (like temperature, pressure, wind speed, wind direction, humidity, sunshine, cloud formations, rainfall or snowfall, etc.) from various sources and prepares the weather report.
The times of sunrise and sunset also change during the year. During summer, sunrise is early and the sunset is late. Due to this, days are longer in summers and nights are shorter. On the other hand, during winter the sunrise is late but the sunset is early Due to this, days are shorter in winter but nights are longer. From this discussion we conclude that days are shorter in winter than in summer.
Weather Over a Week
Let us cut out the weather reports of the last one week from any newspaper. We now record the information regarding temperatures, humidity, and rainfall given in these weather reports in the form of a table. As an example, the weather data for a full week at Delhi is given in the following table.
Weather Data of a Week (at Delhi)
| Date | Temperature | Humidity | Rainfall | ||
| Maximum | Minimum | Maximum | Minimum | ||
| 01.11.08 | 33.1°C | 17.4°C | 75% | 30% | Nil |
| 02.11.08 | 32.8°C | 17.2°C | 88% | 32% | Nil |
| 03.11.08 | 32.1°C | 17.5°C | 73% | 28% | Nil |
| 04.11.08 | 33.0°C | 16.0°C | 82% | 29% | Nil |
| 05.11.08 | 33.5°C | 15.0°C | 86% | 24% | Nil |
| 06.11.08 | 31.8°C | 16.3°C | 96% | 43% | 2 mm |
| 07.11.08 | 31.0°C | 14.2°C | 84% | 26% | Nil |
From the above table we can see that all the seven days of the week do not have the same maximum and minimum temperatures. Similarly, the maximum and minimum humidity values are also not the same on all the seven days of a week. It is possible that the maximum and minimum temperatures (or maximum and minimum humidity values) may be the same on some of the days of a week but all the parameters are not the same on any two days. There is a considerable variation in the weather data (such as temperature, humidity, rainfall, etc.) over a whole week.
Climate
The scientists called ‘meteorologists’ record the weather at various places everyday. The records of the weather over the past several decades have been preserved. These records help the meteorologists to determine the weather pattern at a place. The average weather pattern at a place taken over a long period of time (say, 25 years) is called the climate of that place. For example, if the temperature at a place is high most of the time, then we say that the climate of that place is hot. And if there is also heavy rainfall on most of the days at that place, then we say that the climate of that place is hot and wet (or hot and humid). Climate is called ‘jalvayu’ in Hindi.
There are four major types of climates in the world : polar climate, temperate climate, tropical climate and desert climate. A brief description of all these climates is given below :
(i) Polar Climate. Polar climate is always very cold. In fact, polar regions have the coldest climate in the world. The air is so cold in polar regions of the earth that water falls there as snow (and not as rain). So, the air contains very little water vapour (or moisture) at the poles. Thus, the polar climate is extremely cold and dry.
(ii) Temperate Climate. A climate which is neither very hot in summer nor very cold in winter is called temperate climate. In temperate climate, there is moderate rain and snowfall.
(iii) Tropical Climate. A climate having very high temperatures and high humidity is called tropical climate. Thus, tropical climate is very hot and humid. There is usually a lot of rain in tropical climate.
(iv) Desert Climate. Desert climate is very hot during the day. There is little rain in desert areas so the desert climate is also dry. Thus, desert climate is very hot and dry.
Every place on the earth has its own climate. Our climate depends on our position on the earth and our distance from the sun. The climate is different at different places around the world because these are not heated equally by the sun. The equator of earth is at the minimum distance from the sun. The regions around the equator of earth called tropical regions (where the sun shines directly overhead) get the maximum heat from the sun and have a very hot climate (see Figure). As a region gets more and more away from the equator (towards the poles), the amount of sun’s heat received by the region goes on decreasing, leading to gradually cooler climates.
The poles of the earth are at the maximum distance from the sun. Due to this, the sun’s rays have to travel much more to reach the polar regions of earth which makes them lose much of their heat. The polar regions of earth (near north pole and south pole of earth) receive the minimum amount of sun’s heat, so the polar regions of earth have an extremely cold climate. We have just said that the climate in tropical regions is very hot whereas that in polar regions is extremely cold. Thus, the tropical regions and polar regions are the two regions of the earth which have extreme climatic conditions.
Factors Which Affect Climate
(i) Temperature and rainfall are the two most important factors which determine the climate at a place.
(ii) Another factor which affects the climate of a place is its altitude : whether it is located on high mountains or on plains (flat ground). A place at higher altitude will have a cooler climate than another place on plains (flat ground). This is why hill stations always have a cool climate.
(iii) A yet another factor which affects the climate at a place is its location with respect to the sea : whether it is located near the sea or far away from the sea. Sea-water heats up slowly and also cools down slowly. This has a moderating effect on the climate of coastal areas. The temperatures in coastal areas are neither very high nor very low.
We will now compare the climates of two places in India which are very far apart from each other. These two places are Srinagar (in Jammu and Kashmir) and Thiruvananthapuram (in Kerala). Before we do that, we should know how to find the mean temperature for a month. The mean temperature for a given month is found in two steps : First we find the average of temperatures recorded during the month. Second, we calculate the ‘average ’ of such ‘average temperatures’ over many years. This gives us the mean temperature for that month. The mean temperatures are found for the ‘maximum’ as well as the ‘minimum’ temperatures for the month.
Srinagar is situated at high altitude on a mountain in the Northern part of India whereas Thiruvananthapuram is situated on plains (flat ground) at sea-level in the South-West part of India. Srinagar is located very far away from the sea whereas Thiruvananthapuram is located’zzezzr the sea. Srinagar is located quite far away from the equator whereas Thiruvananthapuram is comparatively nearer to the equator. So, due to their totally different positions on earth, Srinagar and Thiruvananthapuram have entirely different climates. Some of the information about the climates (mean temperatures and mean rainfall) of Srinagar and Thiruvananthapuram during the whole year is given in the following tables :
If we look at the data given in the above tables carefully, we can easily see the difference in the climates of Srinagar and Thiruvananthapuram.
(i) In Srinagar, the temperatures round the year are neither very low nor very high. Also, the rainfall is neither very low nor very high. Thus, Srinagar has a moderately hot and wet climate. In general we can say that Jammu and Kashmir has a moderately hot and wet climate. It is like a temperate climate.
(ii) In Thiruvananthapuram, the temperatures round the year are quite high. Also, the rainfall is very high. Thus, Thiruvananthapuram has a very hot and wet climate. In general we can say that Kerala state has a very hot and wet climate. Actually, Kerala has a typical tropical climate.
Rajasthan state lies in the Western region of India. In Rajasthan, the temperature is very high during most part of the year, so it is very hot (But during winter, which lasts only for a few months, the temperature is quite low). Rajasthan receives very little rainfall, so it is dry. Thus, the climate of Rajasthan is hot and dry. This is the typical desert climate. The North-East India (like Assam) receives rain for a major part of the year, therefore, we can say that the climate of North-East India is wet.
Please note that climate is not the same as weather. Weather is the day-to-day condition of the atmosphere at a place whereas climate is the average weather pattern at a place taken over a long period of time.