 A reallty humidity and a cloud cover. In the last class we had discussion on atmospheric temperature, how it is being measured and how it is useful to crop protection. In today's class we will discuss something about relative humidity and cloud cover. The humidity does indicate that the presence of water as a vapor in the air. This is very very important. Presence of water vapor we have discussed already in the first class that water vapor and aerosols are present in the atmosphere. In the absence of the atmospheric water vapor the rainfall does not occur. So this is very very important. The water vapor comes from your ocean as well as land surface as well as the plant body as the operation and being circulated in the atmosphere as water vapor. Now for example here whenever a water molecule comes as a vapor from either ocean or plant or land it stays in the atmosphere for 7 to 10 days and beyond that it does not stay in the atmosphere. It may goes as a rainfall or something else. Some recycling is there and it is around 7% in the 4 to 7% in the atmosphere. The vapor water of the water content of the atmosphere. So in this way relative humidity or I can say humidity is very very important. So humidity can be defined as the amount of water vapor present in the air. So it can be defined in 3 ways. One is your absolute humidity. Another one is specific humidity and the third one is relative humidity. In the case of the absolute humidity this is nothing but mass of water vapor per unit volume of the air. What is the quantity of the air within this? What is the quantity of water vapor? Then it can be called as absolute humidity. Specifically you want to specify the humidity then it is called as specific humidity. Here mass of water vapor to the mass of moist air in which the mass of water vapor is contained. This is also very very important. The third one is relative humidity. This is being used normally across different countries by meteorologists. Here the relative humidity indicates the percent of water vapor present in the air in comparison with saturated condition. There is a relative statement. This is a relative statement at a given temperature and pressure. At a given temperature and pressure this is very very important. In agriculture and other biological system we use relative humidity. Suppose for example cattle your thermal humidity index there also we take relative humidity as a common and for competition of all those process. Now relative humidity how it is important to crop production? So there is scale. Relative humidity varies from 0 to 100%. 0 does not occur normally. So it occurs from 20% to 100% relative humidity based on the geographical position of the your place. For example a coastal station is there. Monk, RGH would be always 100% because your water vapor is always fluctuated or increased, enhanced, embowed with your sea water positions. So here when RGH is increased when the RGH is 90%, what will happen to the plant? Leaf temperature get increased and this tomato will get closed and the entry of carbon dioxide found reduced. When carbon dioxide is inhibited there is no photosynthesis. Then further in the absence of these reduced closed tomato there is no transpiration. Then automatically in the pumping mechanism translocation of food material also and the uptake of nutrients get reduced. So this is the case of RGH of higher of scale of 90% and other things. What would be the optimum like we have discussed about cardinal temperature? The optimum temperature required for germination of the seeds. So like that in the optimum relative humidity for grog growth is it falls between 40% and 60%. But we cannot eliminate the high RGH also. High RGH is useful to C4 plants like your maize, zorghum and sugarcane as compared to C3 plants like your rice. So C4 plants the photosynthetic pathway also something different between these two. Hence the high RGH is highly useful to C4 plants and a good amount of interaction between the relative humidity and disease. There is always a thumb rule between the prevalence of RGH and disease, spore initiation and multiplication and growth also. In that way pest and disease crop production everywhere RGH plays vital role and crop grain production. Then what are the instruments being used to measure the relative humidity? See I told already that relative humidity is very very important being used commonly in agriculture and all biosciences. So one is wet and dry bulb thermometer. So this is being operated manually, wet bulb is there, the bulb is getting moist with your cotton threads through water supply. This is a sensitive instrument and dry bulb is normal thermometer. So the difference between normal and wet bulb thermometer gives in the relative humidity. So when you put a moist bulb means there is a depression in temperature because of the air saturation. So by this reading we can able to understand relative humidity. There is another instrument wireless thermometer. If you rotate like an instrument it records the air relative humidity and you can get the standard reading. Then another one is hygrometer small instrument being used in all laboratories as well as in farmers field also. Australia and everywhere we can see hygrometer at common place and everywhere people can understand the relative humidity of a particular domain or a location. Then like chart hygrograph is also there auto. It gets moved through a drum. So relative humidity is being recorded across a day 24 hours in a time scale. This is also very important to find out or to record or to find out to compute your weather forecast for certain area where the disease is epidemic rather than endemic. This is very very important and there are also sensors being fitted in the automatic weather station which is being used to record your relative humidity. So next one is because of the relative humidity you get clouds. Cloud is very very very very very important. In the absence of the clouds there is no rainfall. I was discussing about Bergeron ice crystal theory as well as your collision and covalences theory where I was saying about the clouds, cold clouds and warm clouds. So in that way clouds are very very important. In general there are three types of clouds in the atmosphere. Three types of clouds. One is your lower clouds which is always seen in the troposphere. This is up to 2 km in the troposphere. Example status cumulus cumulonimbus. Cumulonimbus is a dangerous cloud. This is very very very vulnerable to all accidents and all heavy rainfall also. Then middle clouds from 2 to 7 km in the troposphere. Examples are altocumulus, altostatus and nimbostatus. Altos means middle. Then high clouds it stays from 7 to 13 km in the troposphere. Example serocumulus and serostatus. If you observe the clouds daily and you can say if you observe the sky daily you are the best skillful man to say these are the clouds. Normally rain we get rainfall from the low clouds that is your status cumulus and cumulonimbus. And rarely we get rainfall from the middle clouds and no rain could be anticipated from the high clouds. So clouds can be related to your rainfall. Next one is cloud cover. Cloud cover is very very important reason for why cloud formation occurs. In the absence of the clouds there is no rainfall. For artificial rainfall making process cloud is must. So let me define the clouds. See increase in temperature in the case of the convective process. When we were discussing about the rainfall, convective rainfall, increase in temperature would increase the capacity of air to hold water as water vapor. This encourages cloud formation. So this reduces the radiation received and provide cooling effect also. So clouds are sometimes very important. Sometimes it is not very very important. Because in the cloudy environment you get best fluctuation of the best. In the cloudy environment there is no translocation of material in the plant system. There are limitations, there are positive and negative impacts from the clouds. But in a clear season, the normal season, if you find the clouds it is mainly due to increase in CO2 and aerosols. Which are not ecologically important. So that is always dangerous. So present days we feel that the carbon dioxide is getting increased. And aerosols also getting increased. According to last week paper the aerosols pollution is more than 429 milligrams per cubic meter of your material airspace. So this is not an engageable statement we could see from the paper. Then cloud cover is like temperature. Temperature is measured in degree centigrade, foreign heat, rainfall is millimeter. Cloud also being estimated in ACTA, O-C-T-A. The scale is from 1 to 8. If the ACTA is 8, then the sky is covered with cloud. If the ACTA is 0, it is a clear sky. So the cloud cover as I indicated earlier, it has got good relationship with the plant nutrition as well as present disease occurrence in crop plants. With this today we complete the class on the your relative humidity and cloud cover. In the next class we could see something about the build. Thank you very much.