Lightning is a natural phenomenon that is basically a combination of the massive spark of electricity in the atmosphere between clouds, ground, or air; and accompanied by thunder generated from shock waves. The characteristics and happenings inside a lightning strike are quite complicated. This oldest natural phenomenon is basically divided into two major types – Ground to Cloud & Cloud to Ground; and the Ground to Cloud lightning strike is more destructive. Mostly, large hurricanes, heavy storms & snowstorms, surface nuclear detonations, volcanic eruptions, wildfires, and so many other things are responsible for lightning and thunder. Frequent rapid changes of temperature over the high altitudes as well as macro-particles like graupels combinedly participate in developing each lightning strike. This magical element of nature apparently creates illusions, or even possesses a catastrophic look anytime, at any moment.
Why it Happens:
Theories and conceptual models provide a vivid picture of how lightning forms and what are the possible catalysts. In the regions of deep convection, macro-particles collide with macro ice particles that provide them with charge differentials. Thus, it creates an upper negative charge region, an upper positive charge region, and a main negative charge region in-between -20 degree Celsius to 0 degree Celsius, following the range of the storm. Generally, ice particles travel faster in updrafts carrying charges than the graupels. There are four major charge regions & more than four charge regions in updrafts and outside outdrafts consecutively. These charge-carrying particles and charge regions make lightning happen in a storm cloud. The negative charge region at the lower part of the clouds generates a Cloud to Ground lightning strike. Moreover, thunder is the by-product of lightning. The lightning channel creates a heated air situation of over 50,000 Fahrenheit which is responsible for an instant air vacuum. This giant pressure caused by an air explosion creates a shock wave, and as sound travels slower than light, we hear the sound some moments later the lightning, which we call Thunder. Thunder can beheard up to 25 miles away from the lightning.
Statistics:
An interesting fact is that approximately 100 lightning strikes occur every second globally. However, this is obviously a natural calamity and it creates death tolls over the planet every year. Let’s have a look at the stats of lighting strike effects on Bangladesh.
| Division | 2015 | 2016 | 2017 | 2018 | 2019 |
| Dhaka | 19 | 15 | 18 | 14 | 20 |
| Chittagong | 05 | 10 | 07 | 04 | 08 |
| Barisal | 04 | 09 | 12 | 05 | 13 |
| Khulna | 12 | 15 | 08 | 13 | 17 |
| Sylhet | 09 | 17 | 10 | 15 | 06 |
| Rajshahi | 15 | 12 | 07 | 11 | 19 |
| Mymensingh | 05 | 14 | 11 | 05 | 08 |
| Rangpur | 17 | 12 | 15 | 09 | 10 |
Lightning causes death toll during different kinds of activities:
| Activities | 2016 | 2017 | 2018 | 2019 | 2020 |
| Fishing | 13 | 18 | 08 | 14 | 10 |
| Playing outside | 02 | 06 | 03 | 01 | 08 |
| Working in the field | 47 | 26 | 35 | 22 | 16 |
| Harvesting Crops | 02 | 02 | 05 | 07 | 12 |
| Others | 21 | 30 | 24 | 18 | 20 |
Lightning Prevention System:
1) Ionizer
2) Earth Electrode
3) Earth current collecting wire
Dissipation wire: The chemical rod used here consists of copper. The inorganic salt will be filled inside the pipe. The salt will ooze out through the border of the pipe surface. The salt creates increased conductivity due to the chemically synergistic effect. It is used in the ionizer.
Assume there is a paddy field of size 500×500 m2. The grounding system and the
ionizer will be installed at the center of the field. Before lighting, the negative charge will be at the surface of the cloud. And for the negative charge’s attraction, the positive charge will be created by inductance across the ground. The grounding system will accumulate the ground charges in it. For this, the grounding system will have no active charge. The positive charge then passes through the ionizer at the top. When the negatively charged electrons come through the ground, they get discharged at the top of the ionizer. Thus, the surroundings of the ionizer-grounding system will be safe from lightning. Because at that time, the positive charge density at the top of the ionizer is higher and the surrounding ground will have a charge of nearly zero, and electrons get attracted by the higher density positive charge. If the model is installed in the field, the farmers around the structure (based on the model) will be safe from lightning strikes. The success rate of this model is 98.6%. The system needs no power to run.
Area-wise Analysis:
High-rise buildings attract lightning strikes frequently, and therefore, lightning strikes are more likely to hit big cities like Dhaka. In hilly areas, clouds are comparatively closer to the ground than in the plains. Therefore, lightning strikes are more frequent in hilly areas, such as Sylhet and Chittagong hill tracts. Thunder and lightning are actually common in the wintertime. Lightning strikes in the Arctic region increased up to 0.4% in 10 years. Lighting rates will increase 12 percent per every degree Celsius or 20 F rise in global temperatures. Lightning doesn’t strike the water bodies as much as land, rather, the charge is dissipated across and near the surface of the water. Lightning hits open farmlands in a high volume, so, casualties from lightning strikes are often observed in Rajshahi and Rangpur regions. The total lightning flashes increase as the relative humidity increases from 60 – 90%. So, the Khulna, Cox’s Bazar, and the Southwestern part of Bangladesh get hit by lightning even more. As tropical forests and tropical regions are more prone to lightning, Bangladesh is more vulnerable to lightning strikes and thunders.
Lightning Forecasting Models:
Latitude-altitude and seasonal things are involved with lightning. When the humidity in the air is higher, the air gets more water vapor. The resistivity of the air is 1.3×1016 to 3.3×1013 ohm-m and the water has a resistivity of nearly 2×107 ohm-m. That means water is more electron conductive. So, the chance of lightning strikes highly increases in such higher humid areas. Also, lightning can occur in relatively higher temperatures. In the air, resistance decreases with increasing temperature, which is an exception to generic metals like Cu, and Zn. Because air conductivity is very low (3×10-5), and when the heat increases, more electrons can pass through the conduction band. Thus, lightning chances increase with temperature rise and vice versa. These parameters can be calculated by Radiosonde Observation. The sensors in the Radiosonde take measurements of surrounding temperature, pressure, and humidity, providing an atmospheric profile up to roughly 15 km altitude. GPS tracker can detect the wind speed. Calculating these physical terms and indexes, lightning strikes can be predicted earlier. The Geostationary Lightning Mapper (GLM) is a satellite that can monitor the cloud’s condition and movement. It has a continuous observation of the pattern of clouds and lightning in every dimension within its coverage area. The advanced artificial intelligence of satellites can detect possible lightning by the resurrection of lightning patterns in specific areas and times. When the satellite can detect possible lightning, it will send the signal to that area. Lightning causes the cloud’s inner turbulence. One possible lightning prediction is to detect the turbulence in the cloud’s molecules. A device can be set up from which UV waves can be sent from the ground to the cloud for monitoring the inner-cloud movement. When the velocity inside the cloud particle becomes higher, interaction and collision will happen inside the cloud, creating a positive-negative charge difference that results in lightning strikes. In this UV cloud detection method, lightning can be forecasted from the ground or from commercial airplanes as well.
Abdullah Al Muhaimen is a student of Notre Dame College, Dhaka
