A day of tides, worldwide - Earth Science



Tides Around the World!A day of tides, worldwideTides are caused by gravitational interactions between the Earth, Sun, and Moon. Both the Sun and Moon influence tides on Earth and result in “bulges” in Earth’s oceans that changes depending on the orientation of the Sun and Moon (see figure 1). Since the Moon revolves around the Earth, this orientation changes over the course of the month, causing larger or small tidal bulges. Meanwhile, the Earth is also rotating on its axis, once every 24 hours. Let’s see if we can identify and make sense of patterns in tidal data for different locations around the Earth.Figure 1. Schematic diagram of (exaggerated) tidal bulges created by the Moon.A note on timekeeping and time zonesWhen we say, “It’s twelve o’clock noon,” we are probably referring to local time. Local time is probably most useful to us in our daily lives: maybe we get up at 6 o’clock in the morning, eat lunch at 11:30, get out of school at 3 o’clock or 4 o’clock in the afternoon, and go to bed by nine in the evening. If you’ve ever traveled far enough east or west from your home, maybe you’ve entered a different time zone. In different time zones, we shift “local time” so that it makes sense for that place on the planet. If we didn’t have different time zones, then “twelve o’clock noon” at one place on the Earth would be light outside, while on the other side of the Earth it would be pitch dark! Instead, we shift the time so that “twelve o’clock noon” means approximately the same thing everywhere on the planet.The Earth is divided into about twenty-four different “time zones”; each time zone is an hour different from the ones next to it. The United States (including Alaska and Hawaii) spans six time zones, while Russia spans a whopping nine time zones! (When it is morning in Moscow, people on the other side of the country are finishing their day!)In this activity, we will be using “Coordinated Universal Time,” or UTC, based on “Greenwich Mean Time” or GMT. This is different from local time, because local time represents the time at a particular location on the Earth. When it is “12 o’clock noon UTC,” that is the case for everywhere on the planet. Each time zone is defined by its difference from GMT (for example, Pacific Standard Time is UTC minus eight hours). By using UTC, we can compare graphs across the world. In addition, UTC and local time can be represented by either a “12-hour clock” or a “24-hour clock.” The 12-hour clock divides the 24 hours in a day into two 12-hour periods. Time ranging between midnight and noon is denoted with AM (ante meridiem) and the second 12-hour period that ranges from noon to midnight is denoted with PM (post meridiem). The 24-hour clock is a convention that runs from midnight to midnight and is divided into 24 hours indicated by the hours passed since midnight and ranges from 0:00 to 23:59 (11:59 PM). Thus, noon in both the 12- and 24-hour clock is 12:00. However, 1:00 PM using the 12-hour clock would be equivalent to 13:00 using the 24-hour clock. Graphing the tides (work with your partner)You will be assigned a dataset for a particular location on the Earth, starting at 00:00 (midnight) UTC December 30, 2015 and ending nearly two days later at 22:00 UTC on Dec. 31. Your location’s time zone (as measured from UTC; for example, “UTC –8 hours” for Pacific Standard TIme) will also be listed. You should determine the local time (using the 24-hour clock) and record it on the data table. Plot ocean height on the Y-axis versus time on the X-axis. Note that “ocean height” is a relative number (above or below a chosen “zero point”). Think carefully about the scale and range of your Y-axis before plotting your dataset! The X-axis is labeled with time in UTC. You should also add the local time to the x-axis labels.Analyzing your data What is the time interval between high tides? What is the time interval between low tides?Can you predict when the next high tide will occur?The tidal range for a region is the difference in height between high tide and low tide. What is the tidal range for your location?Gallery walkWhen everybody has finished graphing their dataset, line them all up in order of time zone, and look for patterns. What do you see that is similar between each dataset? What is different? Are they different in systematic ways?Guiding questions Do all regions experience tides at the same time?Are there differences between the tides in different locations? What could make the tides different?Do all the locations experience about two tidal cycles (low tide, high tide) per day?Hilo, Hawaii (local time is UTC –10 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:000.266Dec 30. 201502:000.405Dec 30, 201504:000.478Dec 30, 201506:000.429Dec 30, 201508:000.239Dec 30, 201510:000.198Dec 30, 201512:000.363Dec 30, 201514:000.622Dec 30, 201516:000.820Dec 30, 201518:000.794Dec 30, 201520:000.561Dec 30, 201522:000.332Dec 31, 201500:000.232Dec 31, 201502:000.341Dec 31, 201504:000.475Dec 31, 201506:000.485Dec 31, 201508:000.367Dec 31, 201510:000.276Dec 31, 201512:000.326Dec 31, 201514:000.501Dec 31, 201516:000.694Dec 31, 201518:000.676Dec 31, 201522:000.291Woods Hole, Massachusetts (local time is UTC –5 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:000.186Dec 30. 201502:000.401Dec 30, 201504:000.539Dec 30, 201506:000.418Dec 30, 201508:000.436Dec 30, 201510:000.324Dec 30, 201512:000.288Dec 30, 201514:000.528Dec 30, 201516:000.805Dec 30, 201518:000.652Dec 30, 201520:000.467Dec 30, 201522:000.353Dec 31, 201500:000.267Dec 31, 201502:000.352Dec 31, 201504:000.617Dec 31, 201506:000.674Dec 31, 201508:000.472Dec 31, 201510:000.430Dec 31, 201512:000.365Dec 31, 201514:000.305Dec 31, 201516:000.516Dec 31, 201518:000.515Dec 31, 201520:000.373Dec 31, 201522:000.338Monterey, California (local time is UTC –8 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:000.771Dec 30. 201502:000.176Dec 30, 201504:000.015Dec 30, 201506:000.422Dec 30, 201508:001.008Dec 30, 201510:001.378Dec 30, 201512:001.319Dec 30, 201514:000.994Dec 30, 201516:000.834Dec 30, 201518:000.987Dec 30, 201520:001.248Dec 30, 201522:001.286Dec 31, 201500:000.957Dec 31, 201502:000.445Dec 31, 201504:000.144Dec 31, 201506:000.366Dec 31, 201508:000.871Dec 31, 201510:001.325Dec 31, 201512:001.396Dec 31, 201514:001.137Dec 31, 201516:000.850Dec 31, 201518:000.808Dec 31, 201520:001.015Dec 31, 201522:001.187Sitka, Alaska (local time is UTC –9 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:002.856Dec 30. 201502:002.208Dec 30, 201504:000.810Dec 30, 201506:00-0.107Dec 30, 201508:000.176Dec 30, 201510:001.454Dec 30, 201512:002.571Dec 30, 201514:002.644Dec 30, 201516:001.837Dec 30, 201518:000.974Dec 30, 201520:000.995Dec 30, 201522:001.792Dec 31, 201500:002.517Dec 31, 201502:002.376Dec 31, 201504:001.331Dec 31, 201506:000.365Dec 31, 201508:000.267Dec 31, 201510:001.205Dec 31, 201512:002.343Dec 31, 201514:002.814Dec 31, 201516:002.310Dec 31, 201518:001.481Dec 31, 201520:001.127Dec 31, 201522:001.549Kwajalein, Marshall Islands (local time is UTC +12 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:00-0.024Dec 30. 201502:000.081Dec 30, 201504:000.567Dec 30, 201506:000.994Dec 30, 201508:001.029Dec 30, 201510:000.543Dec 30, 201512:000.002Dec 30, 201514:00-0.051Dec 30, 201516:000.275Dec 30, 201518:000.672Dec 30, 201520:000.822Dec 30, 201522:000.516Dec 31, 201500:000.157Dec 31, 201502:000.090Dec 31, 201504:000.380Dec 31, 201506:000.837Dec 31, 201508:000.953Dec 31, 201510:000.630Dec 31, 201512:000.200Dec 31, 201514:00-0.006Dec 31, 201516:000.179Dec 31, 201518:000.547Dec 31, 201520:000.743Dec 31, 201522:000.654Saint John, Canada (local time is UTC –4 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:001.3Dec 30. 201502:001.6Dec 30, 201504:004.4Dec 30, 201506:007.2Dec 30, 201508:007.1Dec 30, 201510:004.8Dec 30, 201512:002.0Dec 30, 201514:001.7Dec 30, 201516:004.1Dec 30, 201518:007.0Dec 30, 201520:007.4Dec 30, 201522:005.2Dec 31, 201500:002.2Dec 31, 201502:001.3Dec 31, 201504:003.3Dec 31, 201506:006.2Dec 31, 201508:007.4Dec 31, 201510:005.8Dec 31, 201512:003.0Dec 31, 201514:001.6Dec 31, 201516:003.0Dec 31, 201518:005.8Dec 31, 201520:007.3Dec 31, 201522:006.1Cairns, Australia (local time is UTC +10 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:001.95Dec 30. 201502:002.34Dec 30, 201504:002.35Dec 30, 201506:002.06Dec 30, 201508:001.66Dec 30, 201510:001.47Dec 30, 201512:001.47Dec 30, 201514:001.57Dec 30, 201516:001.63Dec 30, 201518:001.58Dec 30, 201520:001.48Dec 30, 201522:001.50Dec 31, 201500:001.76Dec 31, 201502:002.08Dec 31, 201504:002.26Dec 31, 201506:002.17Dec 31, 201508:001.85Dec 31, 201510:001.51Dec 31, 201512:001.36Dec 31, 201514:001.44Dec 31, 201516:001.59Dec 31, 201518:001.72Dec 31, 201520:001.71Dec 31, 201522:001.64London Bridge, England (local time is UTC +0 hours)DateTime (hh:mm, UTC)Local Time (hh:mm)Water Level(m, relative)Dec 30, 201500:002.01Dec 30. 201502:004.71Dec 30, 201504:006.41Dec 30, 201506:005.64Dec 30, 201508:003.25Dec 30, 201510:001.28Dec 30, 201512:001.02Dec 30, 201514:003.69Dec 30, 201516:006.05Dec 30, 201518:006.10Dec 30, 201520:003.50Dec 30, 201522:001.66Dec 31, 201500:001.56Dec 31, 201502:004.12Dec 31, 201504:005.84Dec 31, 201506:006.11Dec 31, 201508:003.77Dec 31, 201510:001.82Dec 31, 201512:000.90Dec 31, 201514:002.91Dec 31, 201516:005.26Dec 31, 201518:006.39Dec 31, 201520:004.11Dec 31, 201522:002.20Pago Pago, American Samoa (local time is UTC –11 hours)DateTime (hh:mm, UTC)Water Level(m, relative)Dec 30, 201500:000.746Dec 30. 201502:000.499Dec 30, 201504:000.438Dec 30, 201506:000.661Dec 30, 201508:000.924Dec 30, 201510:001.076Dec 30, 201512:000.884Dec 30, 201514:000.57Dec 30, 201516:000.374Dec 30, 201518:000.51Dec 30, 201520:000.752Dec 30, 201522:000.946Dec 31, 201500:000.863Dec 31, 201502:000.623Dec 31, 201504:000.423Dec 31, 201506:000.521Dec 31, 201508:000.791Dec 31, 201510:000.974Dec 31, 201512:000.941Dec 31, 201514:000.658Dec 31, 201516:000.448Dec 31, 201518:000.447Dec 31, 201520:000.652Dec 31, 201522:000.867 ................
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