Weather Monitoring by IMD | 30 Jan 2024

Source: TH

Why in News?

Recently, The India Meteorological Department (IMD) issued a warning about a strong probability of "very dense fog" in Haryana, Chandigarh, and Delhi.

• IMD has also accompanied alerts with maps from the INSAT 3D satellite, and sometimes from the INSAT 3DR satellite.

What is INSAT-3DR?

• About:
  • The IMD uses INSAT -3D and INSAT-3DR satellite data for weather forecasting/monitoring purposes.
    • INSAT-3DR, similar to INSAT-3D, is an advanced meteorological satellite of India configured with an imaging System and an Atmospheric Sounder.
      • An atmospheric sounder measures how the physical properties of a column of air vary with altitude.
      • It has several infrared channels from longwave to shortwave bands and one visible band.
  • The significant improvements incorporated in INSAT-3DR are:
    • Imaging in the Middle Infrared band to provide nighttime pictures of low clouds and fog.
    • Imaging in two Thermal Infrared bands for estimation of Sea Surface Temperature (SST) with better accuracy.
• Mechanism of Imaging System of INSAT-3DR:
  • RGB (Red, Green, Blue) Imager: The colouration of images from the RGB imager on the INSAT 3D satellite relies on two factors:
    • Solar Reflectance: It is a ratio of the amount of solar energy reflected by a surface and the amount of solar energy incident on it.
    • Brightness Temperature: It is the relationship between the temperature of an object and the corresponding brightness of its surface.
  • Prediction and Monitoring of Snow and Clouds:
    • While snow and clouds exhibit similar solar reflectance in the visible spectrum.
      • Snow strongly absorbs radiation of the shortwave infrared.
    • The INSAT 3D and INSAT 3DR satellites utilise day and night microphysics modes through their RGB imager.
    • Day Microphysics: Data from INSAT 3D examines solar reflectance at three wavelengths: 0.5 µm (visible), 1.6 µm (shortwave infrared), and 10.8 µm (thermal infrared).
      • The strength of the visible signal determines the amount of green colour.
      • The strength of the shortwave infrared signal, the amount of red colour
      • The strength of the thermal infrared signal, the amount of blue colour.
    • Night Microphysics: This component of the satellite's operation is determined not by a single but by evaluating the strength of the difference between two signals.
      • The computer calculates the amount of red colour based on the difference between two thermal infrared signals.
      • The quantity of green colour varies according to the difference between a thermal infrared and a middle infrared signal.
      • The amount of blue colour is not derived from a difference but is determined by the strength of a thermal infrared signal at a wavelength.

• Measurement of Temperature, Humidity and Water Vapour:
  • By combining day and night microphysics data, the presence of moisture droplets of different shapes and temperature differences over time, can be identified.
  • It is helpful in tracking the formation, evolution and depletion of cyclones and other weather events.
  • INSAT 3D and INSAT 3DR both use radiometers to make their spectral measurements.
    • A radiometer is a device that measures the temperature or electrical activity. Both satellites also carry atmospheric sounders.
    • These are devices that measure temperature and humidity, and study water vapor as a function of their heights from the ground.

What are the Other Weather Forecasting Methods?

• Apart from tracking satellite data, IMD collaborates with ISRO for ground-based observations from the Automatic Weather Stations (AWS), the Global Telecommunication System (GTS) that measures temperature, sunshine, wind direction, speed and humidity.
  • Meanwhile, the Agro-meteorological Tower (AGROMET) and Doppler Weather Radar (DWR) systems augment the observations.
• In 2021, IMD adopted a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall by modifying the existing two-stage forecasting strategy.
  • The new strategy is based on the existing statistical forecasting system and the newly developed Multi-Model Ensemble (MME)-based forecasting system.
  • The MME approach uses the coupled global climate models (CGCMs) from different global climate prediction and research centres, including IMD’s Monsoon Mission Climate Forecasting System (MMCFS) model.
• All these technological strides have been possible since the National Monsoon Mission (NMM) was initiated in 2012.