atmospheric science

Electronics and Instrumentation Laboratory (EIL)

Atmospheric Electrical Conductivity

EIL has carried out atmospheric electrical conductivity measurements from rockets, high altitude balloons and aircraft and at the ground level using indigenously developed Gerdien condensers. We were the first group to obtain continuous atmospheric electrical conductivity profile from ground to mesosphere with a pumped Gerdien Condenser. Rocket measurements showed the effect of solar activity.

The lab has developed Radioactive Potential Equalizer Sensors for measurements of fair weather atmospheric electric fields and cloud electric fields. It has modified the classical inverted Electric Field Mill with an additional electrode for field operation. The additional electrode facilitates quick test and calibration in the field. With suitable change in electronics the Field Mill can be used for measurements of fair weather fields and cloud electric fields. The lab has postolated that near surface atmospheric electrical conductivity is governed by a global phenomenon and not decided by local weather.

Lightning Incidences in Kerala

A study on spatial and temporal distribution of lightning incidence yielded a data bank usefol for identification of lightning prone areas in Kerala. Investigation on cause of high lightning incidences in Kerala showed that lightning scenario in Kerala is different from rest of the country and that the Western Ghats is responsible for convective thundercloud formation. The study revealed that high frequency weather data of the order of 10 minutes (sampling time) or less can distinguish possible convective thunderstorm development.

From analysis of several lightning accidents in Kerala, it was established that in places with high vegetation density a ring conductor is indispensable as compared to usual lightning conductors for external protection of dwellings. The resolts of analyses also illustrated the affinity of metal objects in getting involved in discharges.

Rain Drop Size Distribution

Monitoring of rain rate, drop size distribution and its vertical profile is being carried out using Disdrometers and Micro Rain Radar (MRR). Manual rain gauges are used for daily measurement of liquid watrer from rain while the radar reflectivity factor and microwave attenuation are recorded using MRR. Some of the findings are:

  1. Radar bright band and non-bright band signatures and simoltaneous transition of the slope of the Z-R relation together give a clear method for classification of tropical precipitation as stratiform or convective origin.
  2. TRMM satellite rainfall data agrees well with our data with correlation coefficients of 0.9 and 0.6 for monthly and daily averaged data.
  3. Studies using MRR has shown that as rain drops come down the number of smaller drops decrease and number of larger drops increase indicating the predominance of a coalescence mechanism.

Instruments developed:

  1. Gerdien Condenser
  2. Radioactive Potential Equalizer Sensors
  3. Rain drop charge sensor
  4. Electric Field Mill

Facilities Available:

  1. Micro Rain Radar (Metek, Germany)  for vertical profiling of rain drop size distribution
  2. Laser Disdrometer (Parsivel, Germany) & Impact-type Disdrometer (Distromet, Switzerland) for rain drop size measurement
  3. Condensation Particle Counter – Water / Alcohol based (TSI, USA) for detection of particles from 5 to >3000 nm
  4. Ceilometer CL 31 (Vaisala Oyj, Finland) for cloud base height measurement