29 Jan Prelims Bits: The Science Behind Fog and Thunderstorm
This article covers “Daily Current Affairs,” and the topic details related to “Prelims Bits: The Science Behind Fog and Thunderstorm”
Syllabus mapping:
GS-1: Geography: Geographical phenomena and their features.
For Prelims:
What is fog? What is the mechanism of formation, what are its criteria, and what is the comparison between fog, mist, and smog?
Thunderstorms: definition, mechanism of formation, and conditions and its types.
Why in the News?
The India Meteorological Department (IMD) has forecast dense fog conditions over Uttarakhand, Punjab, Haryana, Chandigarh, Sub-Himalayan West Bengal, and Sikkim today, with similar conditions expected in isolated pockets of Uttar Pradesh, Gangetic West Bengal, Coastal Odisha, and Bihar for the next 2-3 days. Additionally, light to moderate rainfall accompanied by thunderstorms is predicted over Arunachal Pradesh, Assam, and Meghalaya for the next two days. IMD has also projected a rise in temperature by 2-4°C over Northwest, Central, and East India during the next four days. These weather conditions may impact transportation, visibility, and overall climate patterns in the affected regions.
What is Fog?
The World Meteorological Organization (WMO) defines fog as a suspension of very small water droplets in the air that reduces visibility at ground level to less than one kilometer.
Mechanism of the formation of the Fog:
Similar to Cloud Formation: Fog forms like clouds but occurs at the surface rather than higher in the atmosphere.
Cooling to Dew-Point Temperature: Air must cool to its dew-point temperature (the temperature at which condensation occurs) for fog to form.
Condensation of Water Vapour: Invisible water vapour condenses into tiny droplets, creating fog.
Nighttime Cooling: The most common cause of fog is overnight cooling, as the ground radiates heat absorbed during the day.
Ideal Weather Conditions: Clear skies, light winds, and a high-pressure system favor fog formation.
Role of Wind: Too much wind → Low clouds form instead of fog. Too little or no wind → Dew forms on surfaces instead of fog.
Moisture Content in Air:Measured by the dew-point temperature—higher values indicate more moisture. Fog forms when air temperature and dew-point temperature are close together.
Temperature Difference Matters: If the daytime temperature is too high compared to the dew point, nighttime cooling may not be sufficient for condensation.
Classic Fog Formation Pattern: Rain in the evening increases the dew-point temperature. A high-pressure system follows, bringing clear skies and light winds overnight. This setup often results in thick, dense fog.
Types of Fog
| Type | Formation Process | Characteristics |
|---|---|---|
| Radiation Fog | Forms when the ground cools overnight, causing air near the surface to reach the dew-point temperature. | Most common type, occurs under clear skies and light winds. |
| Advection Fog | Forms when warm, moist air moves over a cooler surface. | Common in coastal areas; sea fog is a type of advection fog. |
| Upslope Fog | Forms when moist air is forced up a slope and cools to saturation. | Can occur over mountains, hills, or even gentle slopes. |
| Fogbow | Caused by the refraction and reflection of sunlight in fog droplets. | Similar to rainbows but appears white due to smaller droplet size. |
Comparison Between Smog, Fog, and Mist
| Factor | Smog | Fog | Mist |
|---|---|---|---|
| Definition | A mixture of fog, smoke, and air pollutants | A dense suspension of tiny water droplets reducing visibility | A light suspension of water droplets with less density than fog |
| Main Components | Smoke, dust, industrial pollutants, and fog | Water droplets formed by condensation | Water droplets formed by condensation but in lower concentration |
| Visibility Reduction | Can reduce visibility to a few meters | Reduces visibility to less than 1 km | Visibility remains more than 1 km |
| Color | Yellowish or brownish due to pollutants | Usually white or gray | Appears whitish and thin |
| Formation Process | Forms when pollutants mix with fog in the presence of high humidity and temperature inversions | Forms when air cools to the dew-point temperature, causing condensation | Forms similarly to fog but with fewer water droplets |
| Common Causes | Vehicular emissions, industrial pollution, burning of fossil fuels | Cooling of air, high humidity, light winds, and clear skies | Same as fog but with less moisture and higher visibility |
| Occurrence | More common in urban areas with high pollution | Found in valleys, near water bodies, and low-lying areas | Appears in open landscapes, hills, and near water sources |
| Health Impact | Severe respiratory issues, eye irritation, and lung diseases due to pollutants | Generally harmless but can cause breathing discomfort in sensitive individuals | No significant health impact |
| Impact on Transportation | Causes major traffic, air, and rail disruptions due to extremely low visibility | Reduces visibility, causing travel delays | Minimal impact on transportation |
| Example Events | London’s Great Smog (1952) caused 8,000+ deaths | Common in winter mornings in valleys and plains | Often seen over fields and water bodies in the early morning |
Thunderstorms:
What is a Thunderstorm?
A thunderstorm is a rain shower accompanied by the sound of thunder. Since thunder is produced by lightning, all thunderstorms are characterized by the presence of lightning.
Mechanism of Thunderstorm Formation
Ingredients for Formation: Moisture, Rising unstable air (air that continues to rise when disturbed), Lifting mechanism (e.g., hills, mountains, or air collisions).
Surface Heating: The sun heats the earth’s surface, warming the air above it.
Rising Air: Warm air rises because it is lighter and warmer than the surrounding air. This upward movement is driven by convection.
Cloud Formation: As the air rises and cools, its water vapor condenses into a cloud.
The cloud grows as it continues to rise into colder parts of the atmosphere.
Ice Particle Creation: As the cloud reaches freezing temperatures, liquid water drops freeze into ice particles.
These ice particles grow by collecting supercooled liquid droplets or vapor.
Collision of Ice Particles: When ice particles collide, they build up electric charges.
Some collisions transfer charge, leading to the formation of lightning.
Lightning and thunder: The electric discharge from lightning creates thunder (sound waves), which we hear during a storm.
Thunderstorm Types and Features
| Thunderstorm Type | Features |
|---|---|
| Single-Cell Thunderstorm | – Small, brief, weak storms |
| – Lasts about 1 hour | |
| – Typically driven by afternoon heating | |
| – May produce brief heavy rain and lightning | |
| Multi-Cell Thunderstorm | – Common, garden-variety thunderstorms |
| – New updrafts form along the gust front (leading edge of rain-cooled air) | |
| – Cells usually last 30 to 60 minutes, system can last for several hours | |
| – May produce hail, strong winds, brief tornadoes, and/or flooding | |
| Squall Line | – Group of storms arranged in a line |
| – Accompanied by squalls of high wind and heavy rain | |
| – Can be hundreds of miles long, but 10-20 miles wide | |
| – Less likely to produce tornadoes than supercells | |
| Supercell | – Long-lived (greater than 1 hour), highly organized storms |
| – Features a tilted rotating updraft (mesocyclone), which can extend up to 10 miles in diameter | |
| – Can lead to violent tornadoes (most large tornadoes come from supercells) | |
| Bow Echo | – Radar signature of squall line that “bows out” |
| – May indicate high winds in the middle of the line, with possible brief tornadoes | |
| – Often evolves into a comma-shaped storm complex | |
| Mesoscale Convective System (MCS) | – Collection of thunderstorms that act as a system |
| – Can cover an entire state and last more than 12 hours | |
| – Includes subtypes like Mesoscale Convective Complex (MCC) and Mesoscale Convective Vortex (MCV) | |
| Derecho | – Long-lived wind storm associated with a band of rapidly moving thunderstorms |
| – Produces straight-line wind damage along a swath | |
| – By definition, extends over 240 miles and wind gusts of 58 mph or more |
Prelims Question:
Q.1. Which of the following conditions are prerequisites for the formation of Fog?
1. Cooling of air
2. Low humidity,
3. Light Calm winds
4. Clear skies
5. High temperature
Select the correct answer using the code given below:
(a). 1, 2 and 3 Only
(b). 1, 3, and 4 Only
(c). 2, 4, and 5 Only
(d). 3, 4 and 5 Only
ANSWER: b
Q.2. The term ‘Mesoscale Convective System (MCS) ’ is sometimes mentioned in the news in the context of:
(a) Climate change
(b) Urban Heat Island Effect
(c) Landslides
(d) Thunderstorms
ANSWER: d
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