1. What is surface wind? Describe the factors that affect surface wind.
Surface wind is the horizontal movement of air near the
Earth ’ s surface, caused by differences in atmospheric
pressure. The primary driver of surface wind is the
pressure gradient force, which pushes air from areas of
high pressure to areas of low pressure. However, the wind’
s direction and speed are also influenced by several
factors:
1. Pressure Gradient Force (PGF): Determines the initial
direction and speed of wind. A steeper gradient leads to
stronger winds.
2. Coriolis Effect: Due to Earth’s rotation, winds are
deflected to the right in the Northern Hemisphere and to
the left in the Southern Hemisphere.
3. Friction: Near the Earth’s surface, friction slows down
the wind and alters its direction. This effect is more
pronounced in areas with rough terrain or obstacles like
buildings and trees.
4. Temperature Differences: Differences in temperature
between land and sea, or between day and night, create
pressure variations that drive winds.
5. Geographical Features: Mountains, valleys, and other
landforms can redirect wind flow.
Surface winds play a critical role in weather patterns,
ocean currents, and overall climate dynamics.
2. Explain depression. What weather is associated
with it? Distinguish between depression, cyclonic
storm, and severe cyclonic storm.
A depression is a low-pressure area characterized by
converging air at the surface and rising motion in the
atmosphere. This rising air cools and condenses, leading
to cloud formation and precipitation. Depressions are
often associated with unstable weather, including heavy
rain and thunderstorms.
Weather associated with depression:
• Overcast skies
• Moderate to heavy rainfall
• Thunderstorms
• Strong but not extreme winds
Distinction:
• Depression: Wind speeds between 31-49 km/h;
relatively mild compared to stronger systems.
• Cyclonic Storm: Wind speeds between 50-88 km/h;
causes more intense rainfall and stronger winds.
• Severe Cyclonic Storm: Wind speeds above 88
km/h; associated with destructive winds, torrential rains,
and storm surges, potentially causing significant damage.
Depressions often evolve into cyclonic storms under
favorable conditions such as warm sea surface
temperatures and high humidity.
3. What instruments are carried by a selected ship?
Why should weather observation be recorded at sea?
Ships are equipped with several meteorological
instruments to monitor and record weather conditions,
ensuring the safety of navigation.
Instruments carried by ships:
• Barometer: Measures atmospheric pressure to
forecast weather changes.
• Thermometer: Records air and sea surface
temperatures.
• Hygrometer: Measures humidity levels.
• Anemometer: Measures wind speed and direction.
• Rain Gauge: Records the amount of precipitation.
• Weather Radar: Detects nearby weather phenomena,
including storms.
Reasons to record weather observations at sea:
• Helps avoid hazardous weather conditions, such as
storms or fog.
• Contributes data for global weather forecasting and
climate studies.
• Enhances navigation safety by predicting weather
changes.
• Aids in maritime route planning to minimize fuel
consumption.
• Provides historical weather data, useful for research
and analysis.
Regular observations are critical for maintaining safety
and improving our understanding of weather and climate.
4. What is a cloud? Explain its formation. List and describe in short
the basic types of clouds.
A cloud is a visible mass of tiny water droplets or ice crystals suspended
in the atmosphere. Clouds form when air containing water vapor cools
below its dew point, leading to condensation around microscopic particles
known as condensation nuclei (e.g., dust or salt).
Clouds produced by
1. Turbulence
2. Oreographic Lifting
3. Convection
4. Frontal Lifting
1. Cirrus: High, silvery, feather-like clouds, often appearing red or
yellow at twilight, dimming stars on dark nights.
2. Cirrostratus: Thin, high, whitish clouds forming a veil around the
sun or moon, often creating haloes.
3. Cirrocumulus: High clouds in small, white, flake-like patterns
without shadows.
4. Altostratus: Mid-level grey or bluish clouds that obscure the sun or
moon with a frosted-glass effect, lacking haloes.
5. Altocumulus: White or grey, globular or banded mid-level clouds
with dark shadows, often in regular patterns.
6. Stratus: Low, dark, grey clouds resembling fog but without
precipitation, obscuring the sun and weakening daylight.
7. Nimbostratus: Dark, uniform, wet-looking clouds causing
continuous precipitation, often obscuring the sun.
8. Stratocumulus: Soft, globular grey clouds with dark shadows,
often forming wavy or linear patterns.
9. Cumulus: White, thick clouds with flat bases and cauliflower tops;
can be fair-weather or towering, sometimes causing light rain.
10. Cumulonimbus: Large, grey thunderclouds with an anvil-shaped
cirrus top, associated with heavy storms and great vertical extent
5. What is the error of a barometer? How to correct
barometer reading? State the location of Stevenson
screen.
Barometer errors occur due to factors such as calibration
issues, temperature changes, and altitude. Common errors
include:
• Temperature Error: Mercury barometers are
sensitive to temperature variations.
• Instrumental Error: Caused by mechanical faults or
aging of the barometer.
• Altitude Error: Readings vary based on the height
of the instrument above sea level.
Correction:
• Use temperature correction tables to adjust
readings.
• Apply altitude corrections by referencing sea level
pressure standards.
• Regularly calibrate the barometer against a standard
instrument.
Stevenson Screen Location:
• Placed 1.25-2 meters above the ground.
• Located in open, shaded areas to avoid direct
sunlight, ensuring accurate measurements of temperature
and humidity.
6.Ideal Conditions for the Formation of Tropical Revolving
Storms (TRS):
1. Warm Ocean Waters: Sea surface temperatures above 26°
C provide the heat and moisture needed for the storm to develop.
2. Coriolis Force: TRS forms between 5° and 20° latitude
north or south of the equator, where the Coriolis effect initiates
rotation.
3. Low Vertical Wind Shear: Minimal difference in wind
speed and direction between the surface and upper atmosphere
allows organized convection.
4. High Humidity: Adequate moisture in the
mid-troposphere is essential for sustaining cloud formation.
5. Pre-existing Disturbance: A low-pressure area or tropical
wave provides the initial disturbance for the storm.
6. Converging Winds: Surface winds converge, forcing air
upwards and initiating convection.
How to Track TRS:
1. Satellite Monitoring: Real-time images track storm
development, movement, and intensity.
2. Weather Radar: Monitors rainfall patterns and wind speed
near coastal areas.
3. Data Buoys: Measure sea surface temperatures and
atmospheric conditions.
4. Aircraft Reconnaissance: Provides detailed data on
pressure, wind speed, and temperature.
5. Forecast Models: Use computer simulations to predict the
storm’s path and strength.
How to Avoid TRS:
1. Route Planning: Ships and planes should avoid areas of
known TRS formation during the storm season.
2. Monitoring Alerts: Follow updates and warnings from
meteorological agencies.
3. Early Evacuation: Ensure timely evacuation from affected
areas if necessary.
4. Emergency Preparedness: Stock up on supplies and
reinforce structures in cyclone-prone regions.
5. Education and Training: Increase awareness about storm
safety and survival techniques.
7. Describe the formation of advection fog. Name the
sea areas where this fog is experienced. How can this
fog be predicted by observation at sea?
Advection fog forms when warm, moist air moves
horizontally over a cooler surface, causing the air to cool
to its dew point and condense into tiny water droplets.
This type of fog is common in regions where warm ocean
currents meet cold water or land areas.
Formation:
• Warm air from tropical regions moves over cold
ocean currents or landmasses.
• The cooling of the air leads to saturation and
condensation.
• Calm or light winds help maintain the fog.
Common sea areas:
• Grand Banks off Newfoundland (where the Gulf
Stream meets the Labrador Current).
• Northern Pacific Ocean (near Alaska).
• Coastal regions like California and the North Sea.
Prediction at sea:
• A sudden drop in temperature when warm air meets
a cold water surface.
• High humidity levels combined with light wind
conditions.
• Visual cues like a gradual haze forming near the
surface.
8. Describe atmospheric layers. Why are cloudy nights
warmer than clear nights?
The Earth ’ s atmosphere is divided into layers based on
temperature and composition:
1. Troposphere: Closest to the surface; weather
phenomena occur here. Temperature decreases with
altitude.
2. Stratosphere: Contains the ozone layer; temperature
increases with altitude due to ozone absorption of UV
radiation.
3. Mesosphere: The coldest layer; meteors burn up
here.
4. Thermosphere: Temperature increases with altitude;
contains the ionosphere, which aids in radio
communication.
5. Exosphere: Outermost layer; transitions into space.
Why cloudy nights are warmer than clear nights:
• Clouds act as insulators, trapping heat radiated from
the Earth’s surface.
• On clear nights, this heat escapes into space,
resulting in cooler temperatures.
• The greenhouse effect of clouds prevents rapid
cooling.
9. What is monsoon? What is the duration of monsoon
in Bangladesh, and how do they affect local weather?
A monsoon is a seasonal reversal of winds caused by
differential heating of land and sea, leading to significant
changes in weather patterns. The Indian Ocean monsoon
system is the most prominent, influencing South Asia,
including Bangladesh.
Duration in Bangladesh:
• The monsoon season lasts from June to September.
Effects on local weather:
• Heavy rainfall: Provides essential water for
agriculture but can lead to flooding.
• Increased humidity: Causes discomfort and
supports crop growth.
• Cyclones and storms: Occasionally accompany
monsoon winds.
• Economic impact: Supports farming and
hydroelectric power generation but can disrupt
infrastructure and daily life.
10. State the basic principle of the function of
hygrometers. Explain the importance of reading at
sea.
Principle of hygrometers:
A hygrometer measures relative humidity by comparing
the water vapor present in the air to the maximum amount
it can hold at a given temperature. Common methods
include:
• Wet-bulb and dry-bulb thermometers: The
difference in their readings helps calculate relative
humidity.
• Electronic sensors: Measure humidity changes
using materials sensitive to water vapor.
Importance of readings at sea:
• Helps predict weather phenomena like fog and rain.
• Monitors evaporation rates, critical for cargo ships.
• Ensures the comfort and safety of crew members.
• Assists in studying climate patterns over oceans.
11. Select an area in which sea smoke is a common
occurrence and discuss why the area is favorable to its
formation.
Area: Arctic Ocean and regions near the Labrador
Current.
Sea smoke formation:
Sea smoke occurs when very cold air moves over warmer
water. The warm water evaporates into the cold air,
condensing rapidly into visible water vapor, resembling
steam.
Favorable conditions:
• Extremely cold air masses (common in polar
regions).
• Relatively warm ocean water (often near areas with
upwelling).
• Light winds to mix the air gently without dispersing
the fog too quickly.
Sea smoke is visually striking and often observed in
winter near the Arctic or Antarctic regions.
12. What are sources and Means available for receiving Weather
bulletin onboard Ship? What are information available on these
bulletin? What publications are available onboard for Obtaining
Times of Transmission and Types of messages?
Sources and Means for Receiving Weather Bulletins Onboard Ship:
1. Radio Broadcasts:
• National weather services and NAVTEX transmit meteorological
warnings and forecasts.
• VHF or MF/HF radio telephony provides localized forecasts.
2. Satellite Communication:
• INMARSAT-C SafetyNET and EGC services transmit
meteorological updates.
• Direct satellite imagery (e.g., from NOAA satellites) for detailed
weather data.
3. NAVTEX:
• Automatic medium-range broadcast of navigational and weather
warnings within 300 nautical miles.
4. GMDSS (Global Maritime Distress and Safety System):
• Provides weather information through MF/HF radio, NAVTEX,
and satellite services.
5. Internet Services (when available):
• Access to websites like NOAA, METAREA, and other
meteorological services.
6. Weather Fax:
• Automated receipt of synoptic charts and weather data.
7. Visual and Audio Broadcasts:
• Television or FM/AM radio broadcasts for nearby areas.
Information Available on Weather Bulletins:
• Synoptic and area-specific weather forecasts.
• Warnings of storms, cyclones, fog, or ice.
• Wind speeds, wave heights, and sea states.
• Atmospheric pressure and temperature trends.
• Tropical cyclone advisories and ocean currents.
Publications for Times of Transmission and Message Types:
1. Admiralty List of Radio Signals (ALRS):
• Volume 3: Maritime Safety Information Services.
• Volume 5: GMDSS – Meteorological Broadcasts.
2. ITU List of Coast Stations:
• Contains schedules and types of weather messages.
3. World Meteorological Organization (WMO) Publications:
• WMO No. 558: Manual on Marine Meteorological Services.
4. Ship’s Weather Routing Services Manuals:
• Specific details on accessing customized weather services.
13. State the principle, function, and use of aneroid
barometers.
Principle:
An aneroid barometer measures atmospheric pressure
without using liquids. It uses a sealed, flexible metal
chamber (aneroid cell) that expands or contracts with
changes in pressure.
Function:
The chamber ’ s movements are mechanically linked to a
needle that indicates pressure on a calibrated scale.
Uses:
• Predicting weather: Falling pressure indicates
storms, while rising pressure suggests fair weather.
• Navigation: Assists in identifying pressure
gradients and storm systems.
• Compact and portable, making it ideal for ships.
