METEO (FINALS) Flashcards
act as vast
conveyors of heat, nutrients, and moisture, significantly shaping the Earth’s climate system
Ocean currents
, driven by wind and Earth’s rotation, move warm water from the equator toward the poles
and cold water from the poles back toward the equator
Surface currents
transports warm water from the Gulf of Mexico to the North Atlantic, moderating
the climate of Western Europe, making it warmer than other regions at the same latitude
Gulf Stream
cold currents like the _ bring cool, nutrient-rich waters down the western coast
of North America, which leads to cooler coastal temperatures
California Current
These are large-scale interactions between ocean currents and atmospheric circulation in the Pacific Ocean,
which significantly alter global weather patterns
El Niño and La Niña Phenomena
involves the weakening of trade winds and the warming of the central and eastern Pacific, leading to
increased precipitation in the Americas and droughts in Australia and Southeast Asia.
El Niño
is the opposite, with stronger trade winds and colder-than-normal sea surface temperatures, often
leading to opposite weather extremes (dry conditions in the Americas and wet conditions in Southeast Asia).
La Niña
help distribute moisture, affecting precipitation patterns around the world
Currents
is influenced by the seasonal reversal of winds and the
movement of warm ocean water, causing intense rains during the summer monsoon
Indian Ocean Monsoon
moves deep, cold, and salty water around the
globe. This system regulates long-term climate patterns by redistributing heat and nutrients, and
any disruption (such as from melting polar ice) could lead to significant climate changes
global conveyor belt (thermohaline circulation)
If the _ were to weaken, it could lead
to colder winters in Europe and shifts in global climate patterns
Atlantic Meridional Overturning Circulation (AMOC)
not only regulate temperatures locally but also influence large-scale climate
phenomena, making them essential to understanding global weather patterns. The interaction between
oceans and atmosphere is a key driver in determining weather variability, precipitation patterns, and
long-term climate changes across the globe.
Ocean currents
Climate change is altering traditional ocean current patterns, such as the _. These changes can affect weather patterns, marine ecosystems, and
maritime navigation
weakening of the Gulf Stream or
shifts in the Pacific Decadal Oscillation
is constantly evolving, driven by advances in technology, new discoveries, and the
changing nature of oceanic patterns due to climate change. Continuous learning is vital for professionals in
maritime operations and other fields related to oceanography to stay updated with new development
field of oceanography
allow for real-time monitoring of sea surface heights and ocean current
movements.
Satellite altimetry and drifters
provide critical data on ocean temperature and salinity profiles, improving our understanding of
the deep ocean’s role in heat distribution
Argo floats
and remote sensing tools help in collecting vast amounts of
oceanographic data, facilitating more accurate predictions of ocean behavior and weather patterns
Autonomous underwater vehicles (AUVs)
Changing ocean currents can influence shipping routes, with _ needing
adaptation to new current patterns
optimal route planning
Utilizing updated editions of _ provides the latest information for safe and efficient maritime operations
Reed’s Nautical Almanac, Admiralty Tide Tables, and NOAA Ocean
Current Forecasts
follow regular, cyclical patterns that are influenced by the gravitational forces of the moon, sun, and
Earth’s rotation.
tides
three primary tidal cycles:
Semidiurnal Tides, Diurnal Tides, Mixed Tides
These occur twice daily, with two high tides and two low tides of roughly equal
height within a 24-hour period. This is the most common type of tide and is seen in locations such as
the Atlantic coast of North America
Semidiurnal Tides
In this cycle, there is only one high tide and one low tide per day. are typical in places like the Gulf of Mexico and parts of Southeast Asia
Diurnal Tides
- These involve two high and two low tides per day, but the heights of each tide vary significantly. are seen in regions like the Pacific coast of North America.
Mixed Tides
is the vertical difference between the high tide and the low tide. It is influenced by the relative
positions of the Earth, moon, and sun
tidal range
These occur when the Earth, moon, and sun are aligned during full or new moons. The
gravitational forces of the moon and the sun work together, resulting in the highest high tides and the lowest
low tides, producing a large tidal range
Spring Tides-
tidal ranges
Spring Tides- Neap Tides-
These occur when the sun and moon are at right angles relative to the Earth (during the first and
third quarters of the moon). The gravitational forces partially cancel each other out, leading to lower high tides
and higher low tides, creating a small tidal range
Neap Tides-
In the Bay of Fundy, Canada, which has one of the highest tidal ranges in the world, spring tides can result in a
difference of _ between high and low tides
over 16 meters
Occur when the gravitational pull of the moon (and to a lesser extent, the sun) causes the water to
bulge outward. This happens on the side of the Earth facing the moon, as well as on the opposite side due to
the Earth being pulled slightly away from the water.
High Tides-
x Occur between the high tides when water levels fall. Low tides represent the areas of least
gravitational pull, as the moon’s influence is weakest at the positions roughly perpendicular to the moon-Earth
axis.
Low Tides-
A coastal region like _ experiences semidiurnal tides, with two high and two low tides each
day, with the height difference fluctuating with the lunar cycle
San Francisco Bay
are the horizontal movement of water caused by the rise and fall of tides. These currents are
crucial for navigation, as they can significantly affect a vessel’s speed and course
Tidal currents
The horizontal water movement toward the shore, associated with rising (incoming) tides
Flood Current-
The horizontal water movement away from the shore, associated with falling (outgoing) tides
Ebb Current
The period when the tidal current is at its weakest, occurring between flood and ebb currents
Slack Water-
Tidal Currents
Flood Current, Ebb Current, Slack Water
in narrow channels like the _, tidal currents can reach several knots, strongly influencing
navigation, particularly during flood and ebb tides
Strait of Gibraltar
are primarily driven by the gravitational pull of the moon, with the sun also exerting a significant but
lesser influence. Together, these celestial bodies create the regular tidal patterns experienced across the
globe
Tides
The moon’s gravity causes water to bulge outward on the side of the
Earth facing it, creating a high tide. Due to the Earth’s rotation, a second high tide occurs on the
opposite side. The moon is the dominant force behind the tides because it is much closer to Earth
than the sun
Moon’s Gravitational Influence-
The sun also influences tides, but its effect is weaker due to the greater
distance from Earth. However, during spring tides, when the sun, moon, and Earth are aligned, the
combined gravitational pull results in stronger tides
Sun’s Gravitational Influence-
During a full moon or new moon, the Earth, moon, and sun align, enhancing
the tidal range, leading to higher high tides and lower low tides
Spring Tide Alignment:
provide a consistent basis for measuring and predicting tides, and they are
defined in relation to specific tidal events
Tidal datums
is a reference point from which tidal heights are measured. It is established by averaging
observed tidal data over a specified period, typically over 19 years
tidal datum
most common tidal datums include
Mean High Water (MHW), Mean Low Water (MLW)
The average height of the high water over a specified period (usually 19
years). is often used as a reference point for maritime navigation and coastal development
Mean High Water (MHW)-
The average height of the low water over the same specified period. is used to define the lowest expected tide in a region
Mean Low Water (MLW)-
Other Common Tidal Datums
Mean Sea Level (MSL), Mean Low Water Springs (MLWS), Mean High Water Springs (MHWS)-
The average sea level measured over a long period (typically 19 years), which serves as a baseline for determining elevations in coastal areas.
Mean Sea Level (MSL)-
The average of the lower low waters that occur during spring tides,
which provides a reference for the lowest tides during high tidal ranges.
Mean Low Water Springs (MLWS)-
The average of the higher high waters that occur during spring
tides, providing insight into the upper tidal ranges
Mean High Water Springs (MHWS)-
are physical markers set by surveying organizations to indicate the elevation of a specific tidal datum at a particular location. they provide essential reference points for various applications, including coastal engineering, flood risk management, and habitat restoration.
Benchmarks
are typically determined through long-term tidal observations at tide gauges, which
measure sea level changes over time.
Data collected over a 19-year cycle allows for the calculation of averages, providing a reliable basis for
establishing MHW, MLW, and other tidal datums
Tidal datums
are essential for navigation charts, ensuring safe passage for vessels by indicating safe
water depths.
They are used in coastal development projects to assess flood risk, manage wetlands, and support
infrastructure planning.
helps predict the impact of sea-level rise on coastal areas
Tidal datums
is a powerful tool in oceanography and tidal studies, allowing researchers and
practitioners to decompose tidal observations into their constituent components. This analysis helps
accurately predict tidal patterns and understand the underlying physical processes driving tides
Harmonic analysis
Tides that occur once every lunar day, with a period of approximately 24
hours. The principal diurnal constituent is the K1 tide (solar semi-diurnal)
Diurnal Components-
Tides that occur twice daily, with a period of approximately 12
hours. The major semidiurnal constituents include the M2 tide (principal lunar semi-diurnal), S2
tide (solar semi-diurnal), and N2 tide (larger elliptic lunar tide)
Semidiurnal Components
Tides can be decomposed into various components based on their periodicity. The two primary
categories of tidal components are:
Diurnal Components- Semidiurnal Components
employs Fourier series to express tidal observations as a sum of sine and cosine
functions. This mathematical representation allows for the separation of various tidal frequencies.
Each tidal component has its amplitude (height) and phase (timing), which can be derived from
historical tidal data
Harmonic analysis
The following steps outline a typical process for harmonic analysis
*Data Preparation- Collect and preprocess tidal observations to remove noise and irregularities.i.
*Fourier Analysis- Apply Fourier transforms to the data, breaking it down into its harmonic components.ii.
*Fitting Models- Fit harmonic models to the observed data, estimating the amplitude and phase for each
tidal constituent.
*Validation- Compare predicted tidal heights with actual observations to validate the accuracy of the
harmonic model.
Applications of Harmonic Analysis
*Tidal Prediction- Harmonic analysis provides the foundation for predicting future tides based on historical
data, essential for navigation and coastal management.
*Understanding Tidal Dynamics- By analyzing the components of tides, researchers can gain insights into
how various factors (e.g., gravitational forces, wind, and atmospheric pressure) influence tidal behavior.
*Climate Change Studies- Harmonic analysis helps assess how changing sea levels and climate patterns
might affect tidal ranges and frequencies
are specific values derived from harmonic analysis that describe the characteristics of
tidal constituents at a given location.
Tidal constants
The height of the tidal wave associated with a specific tidal component (e.g., M2, S2).
Amplitude-
The timing of the tidal component relative to a reference point (usually the time of a known high
or low tide)
Phase-
The phase difference between the actual tide observed and the theoretical tide calculated
based on tidal constants. This lag can be due to local conditions such as wind or atmospheric
pressure
Tidal Lag-
Adjustments made to account for the height of the tide at a specific location
relative to the datum (e.g., Mean Sea Level). For example, if a location is 5 meters above MSL, the
calculated tidal height must be adjusted upward by 5 meters
Elevation Corrections-
Adjustments based on local geography, such as the shape of the
coastline or the presence of islands and bays, which can influence tidal behavior
Geographical Corrections-
is the time lag between the theoretical tide and the observed tide
phase difference
The movement of the Earth affects the timing of tides
Earth’s Rotation-
Geographic features, weather patterns, and human activities can shift the timing of
high and low tides.
Local Effects-
To calculate the tide height accounting for phase differences:
- Identify the tidal constants for the location.
- Adjust the timing of the predicted tide based on the known phase difference.
- Use the adjusted phase to determine the expected height of the tide
are theoretical points in the ocean where there is little to no tidal range due to the
rotation of the Earth and the shape of ocean basins. As tides propagate, they rotate around these points,
and tidal heights decrease with distance from the
Amphidromic points
Shallow water affects tidal behavior significantly due to the following reasons:
Friction- In shallow areas, tides encounter more friction, which can lead to a reduction in tidal heights.
Wave Propagation- The speed of tidal waves changes in shallow water, affecting timing and height.
Resonance- In some locations, shallow bays can amplify tidal ranges due to resonance effects
Calculation Steps
- Obtain Tidal Constants- Gather data for the relevant tidal components (M2, S2, etc.) and their
amplitudes and phases. - Calculate Theoretical Tide- Use the constants to calculate the theoretical tidal height at the
specific time. - Apply Corrections- Adjust for phase differences, geographical factors, and shallow water effects
to arrive at a corrected tidal height. - Account for Amphidromic Points- Factor in the proximity to amphidromic points if applicable.
- Predict Currents- Calculate tidal currents based on the height differences and the local
bathymetry (depth of water) to estimate flow rates during flood and ebb conditions.
The captain must refer to tide tables to ascertain the tidal heights and plan the
arrival during high tide to ensure enough draft
Impact on Water Depths-
The captain may need to plot a route that avoids shallower areas that could
become hazards at low tide
Safe Passage Planning-
If a vessel arrives at low tide and the berth has a minimum depth requirement, it may
not be able to dock. The captain needs to coordinate with port authorities to find an alternative berth or
adjust the arrival time
Berth Availability-
Understanding the timing of tides is crucial. If a vessel is scheduled to leave the
port, it must do so when the tide is high enough to safely clear the channel
Timing of Entrances/Exits-
Which of the ff. best describes the concept of “slack water” in tidal current?
C. When there is little to no current
What is the main influence of the moon on Earth’s tide?
B. It pulls water towards itself, causing high tides
- Which tidal cycle is characterized by one high tide and one low tide each day?
C. Diurnal Tides
What tidal range results from the gravitational forces of the sun and moon being at right angles?
B. Neap Tides
Which tidal datum is defined as the average height of low water over a specified period?
A. Mean Low Water (MLW)
How do Argo floats contribute to oceanographic studies?
B. By providing data on temperature/salinity
If the Gulf Stream weakens, which of the ff. could be a potential impact on Europe’s climate?
B. Cooler winters and more severe weather
Which term describes a reference point from which tidal heights are measured?
C. Tidal Datum
What is the primary tidal component that occurs twice daily, with a period of approximately 12 hours?
B. M2
Which tidal current describes the horizontal water movement toward the shore during rising tides?
C. Flood Current
What is the purpose of tidal stream atlases in navigation?
A. To measure sea level, direction, and strength of current
. A vessel is navigating a channel with a significant ebb current. To compensate for the drift, what should the navigator consider?
C. Decrease speed to prevent drift
What might strong wind condition influence the accuracy of tidal height predictions based on tidal constants alone?
A. They may lead to underestimation of high and low tides
C. They can result in either increase or decrease tides
The captain must account for the direction and strength of the tidal current, which can
significantly alter the ship’s course. For example, if the current is flowing east at 3 knots and the ship is trying
to head north at 5 knots, the effective ground speed will be influenced by the current.
Tidal Streams
The captain uses vector analysis to calculate the resultant course. If the ship’s intended
path is 350° at 5 knots, and the current pushes it 3 knots to the east, the effective course might change to
010°
Calculating Drift-
By analyzing current tables and weather forecasts, the captain may decide to wait for a
slack tide or adjust the route to minimize the effect of the current, ensuring a more efficient and safe
passage.
Voyage Planning-
The navigator annotates tidal diamonds on the chart to indicate the expected tidal
heights and times. Each diamond indicates the direction and strength of currents, which can guide the
vessel’s route.
Tidal Information-
