Roll Clouds: The Most Unusual Cloud in the Skies

Turning towards the sky, one can’t help but become mesmerized by beauty and movement of the different clouds that flow across the atmosphere.  One of the most peculiar looking clouds, arcus clouds, are horizontal elongated tube-like clouds that can occur all over the world.  A subgenre of arcus clouds known as roll clouds, are even more atypical as they are detached from any other cloud features.

Roll-cloud
Roll cloud seen on January 25th 2009, on “Las Olas Beach”, located in “Punta del Este”, Uruguay, by Daniela Mirner Eberl.

While roll clouds can occur in many places, such as Germany, Canada, South Africa, Brazil, Uruguay, and even Florida, they are regionally known as “Morning Glory” clouds along the North Australian Coast, more specifically over the Cape York Peninsula and Gulf of Carpentaria.  The clouds are so named as a result of their early morning appearance, and frequently occur during late September and through early October in this region.  These phenomenal clouds may be on the order of 400-600 miles in length, ½ – 1 mile high, and may move as fast as 40 miles per hour.

As with any cloud, moisture must be present in order for water vapor to condense into water droplets.  Morning Glories tend to occur when humidity values are elevated and a clash of different air masses.  Once moisture levels are adequate, these clouds may form as a result of drastic temperature changes in air masses ahead of a thunderstorm, frontal boundary, or sea breeze.

MorningGloryCloudBurketownFromPlane
Morning glory cloud formation taken from a plane near Burketown (plane heading to Normanton) in QLD, Australia, 11 August 2009, by Mick Petroff

To understand the physical nature of a cloud, let’s first take a look at the relationship between air density and temperature.  Cold air is heavier than warm air as a result of more molecules per volume.

density

To better understand this, imagine a 10’ x 10’ unheated room in the middle of a Siberian winter.  For a person to keep warm, they would want to fill this room with as many other people as possible, capitalizing on generated body heat.  Now imagine that same 10’ x 10’ room located in the middle of hot Texas summer day with no available air conditioning.  In this scenario, a person may want to remove a majority of the heat generating bodies.  So if we exchange molecules for people in the above example, cold air has more molecules than warm air in the same amount of space, therefore making cold air denser (heavier) than warm air. This is what makes cold air sink downwards and warmer air upwards by nature.

A sudden influx of cold air can also force warm surface air to rapidly rise, which is often the case of what happens when cold air rushes out ahead of a thunderstorm or when sea breezes occur from differential daytime heating.  A gust front is the downward and outward rush of the colder/heavier air from within a thunderstorm, usually followed by strong winds, heavy rain, and possible hail within minutes.  An extremely strong gust front rush out faster, detaching from the parent storm, and creating a roll cloud.  Sea breeze circulations occur as the sun heats land and sea surfaces differently, creating an onshore flow during the day and offshore flow during the night hours.  When an extremely strong sea breeze occurs in the evening, the elevated chances of a Morning Glory cloud occurs the following morning.

While there’s no shortage of atmospheric phenomena to excite the average observer, it is without doubt that encountering a roll cloud is an incredible sight and definitely on any weather lover’s bucket list.

_____

This article was published in our monthly column within The Triton  newspaper (Nautical News for Captain and Crews), and can additionally be found here.

Advertisements

Cyclone Cook Aims at New Zealand

Cyclone Cook is currently aiming towards New Zealand, with 30-40 kt winds along the East Coast of the North Island and off the East Coast of the South Island.  Winds will become more northerly as the system continues to slide southward through the remainder Friday and into early Saturday [local NZ time]. Winds in excess of 20kts will remain along the North Island through Saturday afternoon [local NZ time], subsiding below 15 kts by Sunday evening/early Monday [local NZ time]

 

Humidity On The Move

Observe the moisture flow in the 1000-500 mb relative humidity [RH] field.

Cool wraparound feature, as the moisture gets transported on the winds toward the departed NE low on the right hand side of the frame. Also notice the connective feature of the departed low tapping into the moisture pool from the Gulf of Mexico [GOMEX].

West coast also seeing an increase in available atmospheric moisture.

Ain’t #weather beautiful?

00-05

Cat 4 Tropical Cyclone Enawo Affecting Africa

Current IR [infrared] satellite and RH [relative humidity] view of Tropical Cyclone Enawo as it crosses Madagascar and into the Mozambique Straight.

The system made landfall as an intense Cat 4 system, with 137 mph winds. Northerly mid-level flow can be seen via the 200mb (yellow), 500 mb (green), and 850 mb (lavender) wind fields.

Drier air on the southern flank of the system will have a hard time moving northward as storm producing convection over the open water will maintain the healthy moisture field around Enawo.

The Real Deal Behind “Daylight Saving Time”

Yes, it’s “Daylight Saving Time” (DST), without the extra “s” at the end of “saving”.  So now that we’ve got this common mistake righted, back to business!

“Fall Back” and “Spring Forward”:  Remember this so-called helpful pneumonic?  It was devised to help one remember how to alter household “timekeepers” by an hour in order to keep you astronomically synchronized.  In short, it was designed to maximize “daytime” hours by capitalizing on the sun’s generosity, which is lavish in the summer and frugal in the winter.  Calendar wise, daylight saving time runs in and around April through October, while November through April is known as “standard time.  For 2017 in the Northern Hemisphere, DST will begin Sunday, March 12th, and end Sunday, November 5th.  The inverse holds true for DST in the Southern Hemisphere.

Northern hemisphere “Daylight Saving Time” schedule through the year.

With the idea borrowed from an Old English proverb, “Early to Bed, early to rise, makes a man healthy, wealthy, and wise”, Benjamin Franklin tossed around the idea in the late 18th century as a means to save on candle usage during the earlier sundown.  He figured, why not start the day an hour earlier to use the light while it was in place, thereby reducing the amount of candles burned.   It wasn’t until the late 19th century that the idea was officially proposed by New Zealander George Hudson, with the idea of giving people more sunlight in the late spring and summer, when it could be best enjoyed.  While the idea was out in the open, it was not favored.  Germany was actually the first country to adopt the process of sommerzeit (literal German for summertime) in the early 20th century.  This was done as a means to “conserve energy” by keeping people outdoors longer.  The practice of DST came and went over the earlier part of the 20th century but eventually made a necessary appearance during a global petroleum shortage in the 1970’s brought on by an OAPEC oil embargo.  Higher prices of oil per barrel forced a smart economic resolution of reducing oil dependence and relying on the natural resource of the sun’s light.  Fast forward to today, with the innovation of smarter energy practices and work hours which know no boundaries, not every country utilizes DST.

Global DST Participants_02

We know the sun doesn’t change its output, so exactly why does the change in the amount of daylight occur?  In an earlier post about spring, we discussed the Earth’s tilt as being the primary reason behind the seasons.  This tilt, in tandem with the Earth’s position around the sun, determines how much daylight each hemisphere receives.  Essentially, the amount of energy from the sun doesn’t change, but our ability to experience it, as a result of our position around the sun, is what changes.

Spring is the transitional season where the Earth changes hands from winter to summer; when the planet begins to learn towards the sun.  Along those same lines, autumn is the transitional season between summer and winter, when the Earth begins the process of tilting away from the sun.  This slow changing tilt towards (away) from the sun yields longer (shorter) amounts of time that a given hemisphere can receive sunlight.  The special day during which the Earth receives its maximum amount of sunlight is known as the “Summer Solstice”, which occurs on June 21 in the Northern Hemisphere and on December 22 in the Summer Hemisphere.

Moving the clock forward in March/April ultimately removes an hour of daylight as we approach spring and summer seasons, when we already get more sunlight. Conversely, moving the clock back an hour in November yields an additional hour of daylight, which becomes especially useful as we approach the fall and winter seasons when the amount of sunlight becomes less.  At the expense of sounding like a financial planner, consider the loss of the hour in the spring, a short term investment strategy for the upcoming fall/winter season gain; save that sunlight for a “rainy” day!

With all of this in mind, the closer one is positioned to the Northern or South Pole, the more likely they are to utilize DST. So, if you don’t like the annual “give” or “take” activity that comes with this practice, its best avoided by moving closer to the tropics, where the length of day and night varies by small enough amounts to negate the need to alter the clocks!

And lastly, just a reminder, don’t forget to move your clocks forward by an hour on Sunday, March 12th.  Ugh.

____________

TL; DR

Daylight Savings Time:  marked by “Spring Forward”, begins in March/April, and means you move the clock ahead an hour, therefore losing an hour.  This is especially painful spring/summer seasons when you feel like you just got robbed!

Standard Time:  marked by “Fall Back”, begins in November, and means you move the clock back by an hour, therefore gaining an hour.  This is especially useful in the fall/winter seasons when a decrease in daylight occurs and you just want your hour back!

____________

Is Today Spring? It is in MY world!

And no I don’t mean because I live in Florida, the land of hot or not-as-hot.  You may have seen social Media sites buzzing with the mention of spring beginning today, March 01. Don’t worry, you’re not confused.  There are indeed different definitions for spring, depending on whether or not you live in the world of meteorology or elsewhere in the “normal” world.

But before we separate the two, let’s take a step back and review the “anatomy” of the seasons.

Most people assume that the seasons are a result of the Earth’s distance from the Sun.  While this initial thought is indeed intuitive, it’s counteracted with the fact that the Earth is actually closer to the Sun during the Northern Hemisphere Winter, and further from the Sun during the Northern Hemisphere Summer.  Take a look!

seasons

The actual reasons we experience the seasons are a result of the Earth’s tilt. Summer and winter seasons yield the expected temperature extremes because the Earth’s tilt allows the Sun to unevenly concentrate its energy.  Think of it this way: More of the solar “wealth” is given to one hemisphere [summer] at the expense of the other [winter].

Consequentially, spring and fall seasons are considered “transition seasons”; more specifically, where the position and tilt of the Earth occurs in such a way that the Sun’s energy is equally distributed between the Southern and Northern Hemisphere [spread the solar wealth, each hemisphere roughly gets the same].

So now that we share a same page of what seasons actually are, let’s get back to the original question:  When does spring start?  “Meteorological Winter” refers to the usual [climatological] coldest three months of the year, which means December, January, and February.  Therefore “Meteorological Spring” begins right after, or today, March 1st!

The majority of the world goes by the astronomical seasons, which follows the Earth’s position around the Sun.  The beginning of “Astronomical Spring”, also known as the “Vernal Equinox” requires the further understanding of what an equinox actually is.

Let’s take a quick science detour for more astronomical anatomy.  The word “equinox” can be further dissected into its Latin roots; “equi” meaning “equal” and “nox” meaning “night”.  Therefore, the definition of an equinox is when the day and night are of approximately equal times around the planet [roughly 12 hrs each, give or take several minutes depending on how close you live to the poles].  Going back to the “Vernal Equinox”, the position of the Earth around the sun during this time usually occurs between March 19 and March 21, and it kicks off the beginning of the calendar version of spring.

equinox

So “Happy Spring” to all my fellow scientists, and to the rest of you, catch you in a few weeks.

____________

TL; DR

Meteorological Spring follows the average temperatures and begins on Mar 1.

Astronomical Spring follows the earth’s orbit around the sun and begins between Mar 19 and Mar 21

____________