Question and Answers

    Question
    marinetales September 5, 2021
    Tides are long-period waves that roll around the planet as the ocean is "pulled" back and forth by the gravitational pull of the moon and the sun as these bodies interact with the Earth in their monthly and yearly orbits. During full or new moons—which occur when the Earth, sun, and moon are nearly in alignment—average tidal ranges are slightly larger. This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is "added" to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are a little higher and low tides are a little lower than average. These are called spring tides, a common historical term that has nothing to do with the season of spring. Rather, the term is derived from the concept of the tide "springing forth." Spring tides occur twice each lunar month all year long, without regard to the season. Seven days after a spring tide, the sun and moon are at right angles to each other. When this happens, the bulge of the ocean caused by the sun partially cancels out the bulge of the ocean caused by the moon. This produces moderate tides known as neap tides, meaning that high tides are a little lower and low tides are a little higher than average. Neap tides occur during the first and third quarter moon, when the moon appears "half full." Whenever the change of tide occur from low tide to high tide at a given place , the tide is said to be flooding. During the period when the water level recedes from high tide to low tide, the tide is said to be ebbing.
    marinetales July 5, 2021
    Following weather phenomenon, if encountered, needs to be reported: (a) The sighting of dangerous ice. (b) Storm force winds of force ‘10’ or over for which no report has been issued. (c) Sub-freezing air temperatures (that could give rise to ice accretion).
    marinetales May 28, 2021
    1. Round the clock accurate monitoring of the vessel's route progress 2. Comparison between actual and alternative routes 3. comparison of actual speed and charter speed 4. obtaining weather related performance of the vessel 5. routed vessels may attract more favorable insurance premiums
    marinetales May 28, 2021
    Following are the reasons - 1. Water in South Atlantic is comparatively cooler at surface level 2. Weak cyclonic circulations (tropical depressions)
    marinetales May 28, 2021
    A Tropical Revolving Storm (TRS) would normally form and develop in following circumstances / conditions - 1. Area where there is large continent with a large expanse of sea area to the eastward 2. Formation would take place between 5-10 degrees latitudes N or S of the Equator 3. Sea temperature higher than 27 deg C
    marinetales September 2, 2020
    The variation in atmospheric pressure reading gives an early indication of the weather that may be encountered depending upon the fact that whether the pressure is rising or falling. For eg rapidly falling pressure reading may indicate formation of low pressure area nearby the vessel and that tough weather is likely to be experienced. Hence, atmospheric pressure readings are quite useful in predicting the weather pattern vessel may encounter.
    marinetales August 23, 2020
    Whirling psychrometer consists of a set of ’dry’ and ’wet’ bulb thermometers. It is used to calculate the Relative Humidity of the atmosphere. In order to get the accurate readings of the dry and wet bulb thermometers, the whirling psychrometer is rotated. This is because the maximum depression of the wet bulb will depend upon the rate of evaporation.And, it is determined that the maximum rate of evaporation will happen when the speed of wind flowing through it is greater than 7 knots. This can be achieved by rotating the whirling psychrometer. Rotation of psychrometer will result in generation of air speed in excess of 7 knots passing by the wet bulb resulting in maximum depression of the wet bulb and hence better readings.
    marinetales May 18, 2021
    The recurving of TRS is the result of the rotation of the earth. A cyclone has two components of angular momenta. One is with respect to its own spin axis and the other is with respect to the spin axis of the Earth. When a body with angular momentum, such as a gyroscope, is subjected to a torque it precesses; i.e., it angular momentum vector rotates. If a body with angular momentum is forced to precess then it is subject to a torque. A cyclone rotates with the Earth and its angular momentum vector is kept pointing vertically because of the rising of warm air in its eye (center). The resulting torque forces the cyclone toward the pole in its hemisphere. But as the cyclone moves toward the pole it gets closer to the spin axis of the Earth. The preservation of angular momentum then results in the cyclone moving faster with respect to the pole and hence starts moving east. Its path has thus recurved.
    marinetales May 18, 2021
    In simple terms, Prognosis means "forecast". A prognostic chart is a map displaying the likely weather forecast for a future time. Such charts generated by atmospheric models as output from numerical weather prediction and contain a variety of information such as temperature, wind, precipitation and weather fronts.
    marinetales May 20, 2021
    Barometric tendency is the amount of atmospheric pressure change during a specified period of time, often a three-hour period preceding an observation. Barometric tendency is composed of two parts, the pressure change and the pressure characteristic. The pressure change is the net difference between pressure readings at the beginning and ending of a specified interval of time. The pressure characteristic is an indication of how the pressure has been changing during that specified period of time, for example, decreasing then increasing, or increasing and then increasing more rapidly. Barometric tendency is most accurately measured by a barograph (pic attached).
    marinetales May 22, 2021
    A tidal bore, often simply given as bore in context, is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay against the direction of the river or bay's current. Bores occur in relatively few locations worldwide, usually in areas with a large tidal range (typically more than 6 meters (20 ft) between high and low tide) and where incoming tides are funneled into a shallow, narrowing river or lake via a broad bay. The funnel-like shape not only increases the tidal range, but it can also decrease the duration of the flood tide, down to a point where the flood appears as a sudden increase in the water level. A tidal bore takes place during the flood tide and never during the ebb tide. See the attached picture.
    marinetales April 15, 2021
    For differentiating between dew and mist letus first understand fog. Fog can be described as a cloud forming very close to or at ground level. It requires air with sufficient moisture to cool or to be cooled to a temperature to achieve condensation. Once condensation occurs, visibility decreases dramatically. It therefore becomes very hazardous. Fog does not necessarily have to be uniform, or widespread. Some areas may have thick fog whilst others may miss out completely. Fog is more common in valleys and near creeks or streams. It also most commonly occurs overnight and during the morning. However, in colder climates where fog is more common, it may last all day. Mist is similar to fog except it may appear more ragged and forms on rainy days with the air saturated due to the amount of moisture. Mist is more common in mountainous and forest regions. Dew is moisture that condenses at the ground level. The layer of air within about a metre above the ground experiences rapid changes in temperature from day to night. Therefore the temperature may be cooler on the ground than the air above. Consequently, the air temperature close to the ground may cool to below the level needed for condensation. Moisture therefore is observed on grass and on the surface of some objects such as those with metal surfaces. If the air above also cools below the condensation level, fog will form.