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86 Cards in this Set
- Front
- Back
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Celestial Sphere
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An imaginary sphere of infinite radius with the earth at it’s center
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CELESTIAL EQUATOR
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Also known as the EQUINOCTIAL. The intersection of the extended plane of the equator and the celestial sphere.
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CELESTIAL BODIES
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Celestial bodies are located throughout the celestial sphere. We are interested in the relative positions and motions of these bodies on this imaginary sphere.
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Visible Sunrise
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When the sun’s Upper Limb (UL) breaks horizon.
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Visible Sunset
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When the sun’s UL dips below the horizon.
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Civil Twilight
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Morning / Evening: When the Sun’s center is 6° below horizon
Civil Twilight is when we have a clear horizon but only the brightest stars are visible. |
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Nautical Twilight
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Morning / Evening: From when the Sun’s center is 12° below horizon
Nautical Twilight is when we have our first opportunity to shoot a celestial fix because we have our first visible horizon. |
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Long summer days (in the northern hemisphere)
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The sun appears to have an elliptical path around the earth, due to the earth’s rotation.
The northern hemisphere gets longer exposure to the sun when it is tilted towards the sun. |
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Parallel of Declination
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In the same way we measure the height of the sun above the celestial equator, so we measure all the celestial bodies -
Remember - Latitude on the surface = Declination in the sky |
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DECLINATION:
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The angular distance North or South from the Celestial Equator
It is the celestial equivalent of Latitude However, there’s a problem. There are billions of stars and even though we only use a fraction of them for fixes, we can’t list the details of where they all are at all times. We need a common reference point….. |
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First point of Aries
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Where the sun’s ecliptic path cuts the celestial equator (21 March – first day of spring)
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HOUR ANGLES
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The location of a celestial body may be identified by the intersection of its Declination and it’s Hour Circle.
The hour circle is identified by an angular distance west of a reference hour circle. There are three different means of locating the hour circle in use: The angular distance west of the Greenwich Meridian, known as Greenwich Hour Angle (GHA) The angular distance west of the vernal equinox (First point of Aries). This angular distance is referred to as Sidereal Hour Angle (SHA) The angular distance west of a local meridian (your position), known as Local Hour Angle (LHA). Hour Angles are always measured WESTERLY from 0-360 degrees |
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Longitude= Hour angle
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Remember: Longitude on the surface = Hour Angle in the sky
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Hour Angle, SHA
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Because the Stars never change their relative position with respect to the First Point of Aries, the SHA of the stars never changes.
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Zenith
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Point on the Celestial Sphere directly above the observers position
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Nadir
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Point on the Celestial Sphere directly below the observers position
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Zenith Nadir Axis
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Line that links the two
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Celestial Horizon
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The plane drawn at a perpendicular angle to the position of the observer from the center of the terrestrial sphere (Earth) - Since the radius of the earth is considered negligible with respect to the celestial sphere, the visible / observer horizon is considered to be the same as the celestial horizon.
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The Sextant
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Used to measure the altitude of celestial bodies
Altitude is the angular distance of the celestial body above the celestial horizon |
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Geographic Position (GP
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If you drew a line from the celestial body through to the center of the Earth, the point where it inpacts the planets surface is called the
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Lat
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the distance from the celestial equator to the observers zenith
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Co-Lat
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the distance from the observers zenith to the closest celestial pole
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Altitude
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The distance from the celestial horizon to the celestial body
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Co-Altitude
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The distance from the celestial body to the observers zenith
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Declination
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angular distance from the celestial equator
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Co-Dec (or Polar Dist)
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distance from the celestial body to the closest celestial pole
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Meridian Angle
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angular distance between observer and celestial body, otherwise known as LHA
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Azimuth angle
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angular distance between the Co-Alt and Co-Lat
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Hs = Sextant Altitude
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the altitude measured by the sextant
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Ha = Apparent Altitude
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The sextant altitude with all the necessary corrections applied
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Ho = Observed Altitude
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final result once all corrections have been applied
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Altitude Intercept Method
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If the end of the two wires were to be walked all the way around the pole, a circle would be formed on the ground.
Circle of Equal Altitude |
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Co-altitude
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star’s angle from the vertical.
Remember: Altitude + Co-Altitude = 90º |
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Thus, if a star has an altitude of 50 degrees, how far are you from its geographic position?
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Co-altitude = 90-Ho = 90 - 50 = 40 degrees
40 degrees * 60nm = 2400 min. of arc The circle has a radius of 2400 nm |
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Circle of Equal Altitude
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Thus, if we know the altitude of a particular star, and its location relative to the earth (which we can determine from the Nautical Almanac), we know that our position must lie somewhere on this circle of equal altitude.
Get 3 of these and you have a fix (hopefully) |
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THERE ARE TWO COMMONLY USED MEANS OF FINDING LATITUDE:
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LOCAL APPARENT NOON
LATITUDE BY POLARIS (NORTH STAR) |
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Local Observers Meridian:
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Your position in Longitude projected onto the Celestial Sphere
When using the sun to check your Gyro you need to know when the sun will pass through that LOM That is known as Local Apparent Noon (LAN) |
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Latitude by Polaris
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Polaris (the “pole star”) is so named because it is nearly coincident with the celestial north pole (Pn).
As a result, the celestial triangle collapses. 90 - Ho = 90 - latitude, therefore Ho = latitude Colatitude and coaltitude are of equal length. The observed altitude of Polaris is equivalent to the observer’s latitude. In reality, Polaris and the celestial Pn are not exactly coincident (3/4° offset). As a result, Polaris wanders a bit with respect to the north pole (due to precession of equinoxes). To account for this, a correction table is provided in the Nautical Almanac. |
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Celnav
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Goal ? …compare your estimated position to a celestial fix using the stars !
How to take a celestial fix ? …Shoot at least 3 stars with a sextant to measure altitude… When to shoot a star ? …mainly during twilights Celestial LOPs ? … a circle |
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The Celestial Sphere
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An imaginary sphere of infinite radius with the earth at it’s center.
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Air Mass
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Extremely large body of air whose properties are fairly similar in any horizontal direction at any given altitude. Which two properties?
Temperature & Humidity (density) Part of weather forecasting is determining… air mass characteristics, predicting how and why they change, and in what direction these systems will move |
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Source Regions—Origin of Air Masses
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Uniform characteristics develop…
in a region that is generally flat and of uniform composition, with light surface winds The longer the air remains stagnant over its source region, the more it acquires properties of the surface below. |
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Humidity & Temperature
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c = Continental
Over land (dry) P = Polar Polar latitudes (cold) m = Maritime Over water (moist) T = Tropical Tropical regions (warm) |
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Basic Stability in the Air
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Humid (moist) air weighs less than dry air—is more buoyant
Warm air is less dense than cold air—more buoyant—wants to rise Dry air weighs more than moist (humid) air—is less buoyant Cold air is more dense than warm air—less buoyant—wants to sink |
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Air Masses: movement, modification & stability
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Air masses move in response to winds aloft…
…becoming modified by surfaces of different temperatures and moisture content You can determine the stability of the air mass… …by how the air mass is being modified by the surface: Hot surface is warming the lower layers of a polar air mass. This leads to what kind of stability? The cold surface is cooling the lower layers of the polar air mass even more. Stability? |
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Tropical air mass?
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Hotter the surface air, the more buoyant it is = unstable = more mixing
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What is a weather front?
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The transition zone between air masses of different densities
Density differences Temperature differences Humidity differences |
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Cold front’s leading edge: Steep
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Fast-moving front - Slope is 1:50
Slow-moving front – Slope much gentler |
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COLD FRONTS: Slow vs Fast moving fronts
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Slow-moving fronts: Gentler slope means clouds form behind the front.
Makes it difficult to determine the surface front position from satellite imagery. |
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Fast Moving Cold Fronts
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have a line of active showers & thunderstorms
“squall line” - develops parallel to & often ahead of an advancing front—producing heavy precipitation & strong gusty winds. The steep slope of the front pushes the weather ahead of the front. |
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Frontolysis
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when the temperature contrast across a front lessens, causing the front to weaken and dissipate
A dying frontal system |
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Frontogenesis
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an increase in temperature contrast across a front can cause it to strengthen and regenerate into a more vigorous system
A frontal system develops or redevelops |
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WARM FRONT
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the slope is much more gentle…1:150 to 1:200. The cloud cover is usually ahead of the warm front.
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Warm-type Occluded Front:
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air behind the occlusion is cool compared to cold air ahead of it.
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What are the 5 ways of locating a front on a surface weather map
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Sharp temperature changes over a relatively short distance
Changes in the air’s moisture content (changes in dew point) Shifts in wind direction Clouds and precipitation patterns Pressure and pressure changes |
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cP, mP, cT, mT, cA, mE, mA?
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cP = continental Polar – dry, cold air
mP = maritime Polar – moist, cold air cT = continental Tropical – dry, warm air mT = maritime Tropical – moist, warm air cA = Continental Arctic = dry, extremely cold cP air mE = Maritime Equatorial = very moist, extremely hot mT air |
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Occluded Front
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When frontal systems are born, there are 2 fronts: a cold front & a warm front.
Cold fronts are usually faster than warm fronts. The cold front catches & overruns the warm front. The collision of fronts produces an occluded front, where some of the most severe weather exists, especially near the triple point, where cold, warm & occluded fronts meet. The occlusion indicates the later stages of a storm’s life cycle. |
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Warm front
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leading edge of warm air (mT or cT)
Heavier, more dense cold air retreats slowly as warm air rides up and over the cold air, producing widespread clouds and precipitation |
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Weather Observations
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Ships required to record regular weather observations:
- Hourly - For ships in company, OTC may designate one ship to report observations – LHA, LHD, CVN, selected CRU/DES have weather personnel embarked - In port, if no manned weather facility within 50NM |
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Synoptic
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Formatted weather message:
- Every 6 hours PRIORITY if: surface wind speeds < 33 kts, seas < 12 feet. - Every 3 hours IMMEDIATE if: surface winds > 33 kts, seas > 12 feet. - Via plain voice: first indications of a tropical cyclone, unusual or hazardous weather. |
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Weather Observations
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prepared by QMOW, QC’d by OOD:
- Type of observation - Cloud Cover (amount, ceiling) - Prevailing visibility - Weather/obstructions to visibility - Sea level pressure in millibars Station pressure in inches of mercury - Sea water temp (at sea water injection, taken by Engineering) - Sea height, direction and period - Ice (if applicable) - Dry bulb temp in degrees Fahrenheit - Dew point temp in degrees Fahrenheit - True wind direction & speed - Clouds by type, quantity, & height - Remarks |
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Services Available
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Tropical Cyclone Formation Alert - situational. Text message and graphical (web page)
2. High Winds & Seas Warning (00/12Z). Graphical (GCCS-M & Web), text message. 3. Local Severe-Storm Warning (CONUS) 4. WEAX: Regional or OPAREA forecast – twice daily. Request in MOVREP. Text/Graphical. 5. Optimum Track Ship Routing (OTSR) – ship specific weather & recommended safe track (Required, Request in MOVREP). |
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Information Sources
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MESSAGE TRAFFIC (WEAX, OTSR, HURREX)
GCCS NIPRNET/SIPRNET Fleet Multichannel Broadcast (Common Channel) |
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Heavy Weather
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Shipboard Actions:
-Heavy Weather Bill -Take winds & seas just off the bow or on the quarter. Avoid beam seas/winds: the “trough” -Low visibility detail /Safety of lookouts /Weatherdecks secured -Stay alert for small craft or other vessels in distress. Listen to radios for distress calls. |
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Signs of Deteriorating Weather
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OOD’s are expected to monitor the weather throughout their watch and keep a close eye on signs of worsening conditions:
-Falling barometer. -Wind direction shifts, increased speed and gusts. -Sea swell period decreasing. -Cloud patterns (Cirrus, cumulonimbus). |
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Identifying weather influences
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When our forces know what weather to expect, they can prepare for & adjust operations:
- IRAQ/Northern Arabian Gulf. Sand storms, thunderstorms. Winter vs. Summer. - RADAR/UHF, HF comms. Atmospherics and anomalies in space can degrade/enhance performance. - FOG. Dew point: temperature at which water cannot evaporate from the air. When it approaches dry bulb (w/in 3°), conditions are ripe for fog/haze. - Sea state and effect on sonar performance. |
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Heavy Weather
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Small Craft Advisory 25-33 mph
Gale Force Winds 34 - 47 mph Storm Force Winds ≥ 48 mph |
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Tornado
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violently rotating column of air extending from a thunderstorm to the ground. Lasts minutes to hours. Appear as funnel shaped cloud. Windspeeds of 150 - 300 mph with extremely low pressure.
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Waterspout
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Similar to tornadoes, occur over oceans or inland waters. Usually weaker, less destructive winds than tornadoes.
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Squall
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strong wind, forms/dissipates quickly, sometimes w/ thunder, lightning & heavy rain
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Monsoons
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Seasonal, steady winds, offshore in winter & onshore in summer. Up to moderate gale force, may induce heavy squalls & thunderstorms in the summer
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Tropical Weather Damage
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TORNADOS
Embedded in T-storms Normally form w/landfall HIGH WINDS Flying debris, missile hazards, High seas TORRENTIAL RAIN/FLOODS More than 6 inches in less than 8 hrs is possible |
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Storm Surge
“WALL OF WATER” |
Storm surge:
An abnormal rise of the sea in advance of or with the cyclone Caused by: - Low pressure at center - Winds in right front quadrant |
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Tropical Cyclone 101
Formation Basins |
Favorable Conditions
Warm water (>80° F) to 150 ft deep Conditionally unstable atmosphere Moist air ~ 16,000 ft 300 nm or more from Equator (5°) Pre-existing disturbance Low vertical wind shear |
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Danger Area
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Reinforce that the best evasion tactic is to stay away from the storm altogether. Proper tracking of the storm is the key.
Describe 35 kt wind radius Explain addition of 120 nm error radius to 24 hr 35 kt wind radius Discuss similar principle for 48 and 72 hour forecasts |
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TROPICAL CYCLONE EVASION
Rule #1: |
Remain far enough away from the Tropical Cyclone so the following rules are not required.
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Key Elements to Determine:
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Position relative to storm center & axis
- Path & velocity of storm’s travel Tropical Cyclones are deflected to the right by Coriolis Effect (Northern Hemisphere), but spin counter-clockwise |
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Dangerous semi-circle:
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Wind greater due to speed
augmented by the forward motion of the storm. |
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“Less Dangerous” semi-circle:
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Wind decreased by forward
motion of the storm. |
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Evasion from Dangerous Semi-Circle
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1) Bring the wind on the starboard bow (45° rel) and hold it there.
2) Make as much headway as possible. 3) If the wind veers (rotates clockwise), change course to hold wind on the starboard bow. 4) The tropical cyclone will pass astern. |
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Evasion from Less Dangerous Semi-Circle
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1) Put the wind on the starboard quarter (130° rel).
2) Make as much Headway as possible. 3) If the wind backs--ship is in the less dangerous semi-circle. If it veers—ship is in the dangerous semi-circle. 4) The storm cyclone will pass astern. |
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Evasion on the Storm Track
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1) Bring wind to the starboard quarter (160°) and maintain course.
2) Run for the navigable semi-circle. 3) If wind direction maintains or veers clockwise slowly, ship is still in the path of the storm. 4) If wind backs (counterclockwise), ship is in less dangerous semi-circle. |
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Tropical Cyclone Conditions of Readiness
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TC CORs or TCCs) are based on the time to onset of destructive winds (50+ kts)
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SORTIE Conditions
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Senior Officer Present Afloat (SOPA) - orders Sortie
Sortie Commander - in charge once underway Sortie Criteria (Per FFC OPORD 2000-07) If sustained winds > 50 kts Avoid heavy seas > 12 ft wave ht Storm surge (high tide) > 4 ft norm COR timeline is based on onset of destructive winds and local considerations SORTIE timeline varies w/different SORTIE plans, ship limits, & 12ft seas forecasts SORTIE & COR timelines do not necessarily correlate to each other |
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WARNINGS
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Frequency (every 6 hours, 03Z, 09Z, 15Z, 21Z)
Methods of Receiving Warning 1. DMS addressed to CAD HURRIWARNLANT (regular message traffic) 2. GCCS-M 3. Autopoll (757-444-0963) 4. NFAX (8080 khz, etc...) 5. Tropical Warning Voice Recording (757-444-7356) |
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Upon Receipt of Warning:
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Plot the current and forecasted 24 hour storm position, and the forecasted radius of 35 kt winds.
Using a compass extend the radius of the forecasted 24 hour 35 kt wind band by 135 NM. Draw tangents relative to the direction of the storm from the 35 kt radius (current position) to the outermost radius at the 24 hr forecast position. Use the same procedure for the 48 and 72 hr forecast positions, however, use 275 and 400 NM radii/respectively, in lieu of the 135 NM value. Avoid the DANGER AREA. |
