RYA Yachtmaster Meteorology 2 — Questions and Answers
Question 1: What weather conditions produce 'lee waves' and how can they affect offshore sailing?
- Flat calm conditions
- Strong winds flowing over mountainous land or islands, creating oscillating waves in the atmosphere that can cause severe localised gusts and turbulence downwind (Correct answer)
- Only thunderstorm activity
- Ocean swells from distant storms
Correct answer: Strong winds flowing over mountainous land or islands, creating oscillating waves in the atmosphere that can cause severe localised gusts and turbulence downwind
Lee waves form when stable airflow is forced over elevated terrain. They can create severe turbulence, strong downdrafts, and localised gusts that are significantly stronger than the general wind, particularly in the lee of islands.
Question 2: What is the significance of 'wind against tide' conditions for offshore sailors?
- It has no effect
- When wind opposes a strong tidal stream, it creates steep, short, breaking seas that can be dangerous even in moderate wind strengths (Correct answer)
- It only affects power boats
- It makes sailing faster
Correct answer: When wind opposes a strong tidal stream, it creates steep, short, breaking seas that can be dangerous even in moderate wind strengths
Wind against tide creates steep, short, confused seas that can be dangerous. The opposing current steepens and shortens the waves, making them break more readily. This is particularly hazardous in tidal races and overfalls.
Question 3: What is a 'trough' in weather chart terms?
- The lowest part of a wave
- An elongated area of low pressure without a closed circulation, often associated with frontal activity and poor weather (Correct answer)
- A dip in sea temperature
- A channel between two islands
Correct answer: An elongated area of low pressure without a closed circulation, often associated with frontal activity and poor weather
A trough is an extension of low pressure shown as a dip in the isobars. It is often associated with frontal activity, wind shifts, and deteriorating weather conditions including rain and increased wind.
Question 4: How does the Coriolis effect influence wind patterns in the Northern Hemisphere?
- It has no effect on wind
- It deflects wind to the right of its path, causing wind to blow parallel to isobars rather than directly from high to low pressure (Correct answer)
- It deflects wind to the left
- It only affects ocean currents
Correct answer: It deflects wind to the right of its path, causing wind to blow parallel to isobars rather than directly from high to low pressure
The Coriolis effect, caused by the Earth's rotation, deflects moving air to the right in the Northern Hemisphere. This causes wind to flow roughly parallel to isobars, creating the characteristic anticlockwise circulation around lows.
Question 5: What is a 'land breeze' and when would an offshore sailor encounter one?
- A strong onshore gale
- A night-time offshore wind caused by the land cooling faster than the sea, creating an airflow from land to sea (Correct answer)
- A constant trade wind
- A wind only found in the tropics
Correct answer: A night-time offshore wind caused by the land cooling faster than the sea, creating an airflow from land to sea
A land breeze develops at night when the land cools faster than the sea. Cool, dense air flows from the land towards the warmer sea. Vessels close to shore may experience this light offshore wind, typically weakest at dawn.
Question 6: What is 'wind shear' and why is it important for sailors?
- A type of sail trim
- A sudden change in wind speed or direction over a short distance or time, which can cause loss of control and dangerous conditions (Correct answer)
- The sound of wind in the rigging
- A tool for cutting rope
Correct answer: A sudden change in wind speed or direction over a short distance or time, which can cause loss of control and dangerous conditions
Wind shear is an abrupt change in wind speed and/or direction over a short distance (horizontal or vertical). At sea, it can cause sudden gusts, heading changes, or loss of wind, making sail handling and boat control challenging.
RYA Yachtmaster Meteorology 2
What weather conditions produce 'lee waves' and how can they affect offshore sailing?