Archive for the ‘Weather hazards’ Category
Citrus County Florida and Hurricanes
Enlarge images in this posting with left clicks.
ILLUSTRATION A. Big Lake Henderson from Inverness, Florida
– Please credit photo to Colin Toney –
ILLUSTRATION B – map of Citrus County showing locations of the Gulf Coastal Lowlands which are subject to storm surges, the sandy Brooksville Ridge occupying more than one-third of the area, and the Tsala Apopka Plain containing the majority of the county’s fresh water lakes –
– TWO INDEPENDENT LEFT CLICKS ENLARGE THE IMAGE ABOVE TO THE FULLEST –
I Am Very Happy Living In Citrus County.
Of course, being retired, being a nature-lover and being relatively healthy helps. All locations have pros and cons but with respect to the latter I have yet to regret the move with my extended family 9 years ago. We had experienced hurricanes and tropical storms through the years. Our house was a total loss in 1992’s category 5 hurricane Andrew; it was at ground zero in Homestead which is located 27.6 miles (as the crow flies) southwest of Miami. The house belonging to my wife’s folks, less than a mile away, had extensive damage. What a terrible mess was caused by the only hurricane to make landfall upon the U.S.A. that season. But when we moved to Citrus County 13 years later we were conscious of the fact that by leaving South Florida we had NOT left “hurricane country.” I felt that Citrus County would be safer in that respect but certainly not a hurricane-proof location. It didn’t take long for me to meet people who felt that there was something special about Citrus and other nearby counties that made a serious hurricane event almost inconceivable.
Complacency is a real problem in hurricane country. I don’t claim to be an expert on complacency but there have been times in my life where I might have contracted the disorder I call “terminal uniqueness.” Therefore, I am acquainted with denial, ignorance, procrastination, irresponsibility, and “living in a dream world” because I’ve been there; for all I know, I’m there still. I believe that every time I point a finger at someone, three are pointing back at me and this is written in that spirit. Thus, I’m not trying to indict anyone here; I’m just trying to state what appears to me to be true.
As I see it – Citrus County, as a whole, though probably not the “geographical poster child” for complacency when it comes to hurricanes and tropical storms, seems to be after the title – in spite of its experience with “The Florida Four in 2004” (see illustration C below). I’m not speaking of those who vigorously engage in emergency planning and increasing awareness in the community. And of course I’m not speaking to residents reading this who have engaged in effective advanced planning and preparation. No, I’m speaking of the average Jack and/or Jill occupying a dwelling in Citrus County; I acknowledge that there are plenty of exceptions. To be sure – this is not a problem exclusive to Citrus County. I believe it’s prevalent in all or nearly all parts of the country susceptible to tropical cyclonic weather. Please click on this graphic below for enlargement.
The four 2004 storm tracks above are dated for your convenience. For example: Tropical storm Bonnie’s track runs from August 3rd to August 14.
NOTE: For an infrared satellite loop of the majority of the 2004 season, click on the first link below. Date and time indicators appear along the bottom margin. Then for an animated loop which is easier to interpret click on the second link.
Some History
I moved to Florida in 1956 during my high school junior year and I don’t remember a time since when I have not been conscious of the potential for tropical weather to wreak havoc upon lives and property and I have always tried to be prepared. If you were to have simply driven by my house you could have observed elements of hurricane preparedness. That is still true today. It is a high priority item in my family. I have been an active advocate of hurricane awareness and preparation for many years. If anything, I hope that illustrations in this weblog posting will increase awareness at least among the few who see it. So let me call your attention to the illustration below. Most residents who see such illustrations are, at the very least, surprised. Naturally some point out that this covers a long period of time. But really, is 161 years a long time in the whole scheme of things? My point in showing this is: TROPICAL CYCLONES ARE A REALITY IN CITRUS COUNTY. Also, please be aware of the fact that the plot lines show the paths of the centers of storms and that the storms have a width that is not apparent here. The center of a storm does not have to come within just a few miles for it to be of great concern; the center can be many miles away.
ILLUSTRATION D -The circle has a 100 mile radius with Inverness, Florida in the center. Remember, left click for enlargement.
Even before leaving Homestead for good in 2005 – while visiting Citrus County I detected the existence of a notion of immunity to any sort of serious tropical cyclonic weather (e.g. hurricanes, tropical storms). Though I have no scientific evidence to back this – I classify the “no-need-to-be-concerned” feeling as widespread among the Citrus County population. In fact, sometimes “low-to-no” hurricane probability has been drastically overstated here (I’ve heard it and I’ve heard about it). It seems that “The Florida Four in 2004 ” did very little to squelch the delusion. Still – I would have expected that particular season to have provided a huge “wake up call.”
NOTE: The “official” Florida Four in 2004 includes hurricane Charley which struck Punta Gorda on August 13 and later moved through South Carolina. It does not include tropical storm Bonnie.
Just a few weeks ago I overheard a hostess at a popular restaurant in adjacent Marion County telling a booth full of patrons, “We just don’t get hurricanes here.” Recently a friend of mine suggested that there was something about our county’s geography, specifically the Brooksville Ridge, that prevented hurricane visits. That reminded me of Muncie, Indiana where I used to live; it is alleged to be immune from tornadoes because of a particular bend in the river flowing through it. Also, a protective blessing from an Indian chief has been cited.
http://www.ballstatedaily.com/article/2013/11/evidence-refutes-claims-of-tornado-myth
“The Florida Four in 2004” did not produce the extent of damage or flooding that raised eyebrows all over the nation and, for now, a sense of security from lethal storms seems to cling on. This is not a prediction nor is it my wish, but I do fear that a hurricane coming through this area has the potential to surprise a lot of people and make them wonder what they were thinking. And such an event could be deadly and most certainly destructive.
Storm Surge Potential
When I was looking for property in Citrus County one of my big concerns was the encroachment of wind-driven sea water with a storm – the so-called storm surge. Upon investigation I found what I expected – that if it was important to me personally to avoid surge potential I should avoid about one-third of the county’s land area – the western third.
NOTE: Illustration B, “map of Citrus County” might be useful to you here.
Most of that western third is undeveloped but there are two noteworthy communities within it, Homosassa and most of Crystal River. Therefore, early on I decided not to settle on the Gulf Coastal Lowlands but instead chose the Brooksville Ridge. In my opinion, the broad, hilly, sandy ridge is, by far, the safest place for a home or business in the county because of it’s higher elevations and greater ability to handle large amounts of precipitation often associated with a storm. The highest point in the county is within the Citrus Hills Golf Course above a 230′ contour – my Google Earth measurement has it at 235 feet.
ILLUSTRATION E – Storm surge portion of Citrus County, the western third (color-coded). T = tropical storm and the numbers represent hurricane categories. Left click to enlarge or go to the next illustration for more detail.
– ILLUSTRATION F – Two independent left clicks result in a significant enlargement.
FOR STORM SURGE ZOOM CAPABILITIES, click on this link:
http://www.floridadisaster.org/publicmapping/SURGE/SURGE_CITRUS.pdf
Other Concerns
To be fair, Citrus county seems not to have been visited by category 5 or 4 hurricanes though at nearby Cedar Key a 1896 hurricane was a category 4 according to some estimates – crediting it with 135 mph winds.
NOTE: As far as we know, only three Category 5 storms have struck the U.S.A. – the 1935 Florida Keys or Labor Day hurricane, Hurricane Camille which hit Mississippi in 1969, and 1992’s Hurricane Andrew. The records aren’t good enough to say whether any earlier storms were Category 5 by today’s standards and they don’t go back very far with respect to the length of time that such storms have visited the North American mainland.
But lesser tropical cyclones, like tropical storms and tropical depressions, can produce both microbursts and tornadoes and simple straight-line gusts can far exceed the sustained wind velocity of such storms. Of course this is true for hurricanes too. Illustration G below shows initiation points of tornadoes spawned by tropical cyclones (e.g. tropical depressions, tropical storms, hurricanes) from 1995 through 2010. The entire report is available in the PDF format here:
– ILLUSTRATION G –
Please enlarge this with a left click. This illustration is on page 7 of Roger Edwards’ report which is available to you as the previous PDF document link titled Tornadoes Tropical Cyclones.
Recently, I looked into the proximity of past storms near my church and created a graphic for those who might be interested. Since the church is located in Lecanto and near the geographical center of Citrus County, I’m including the graphic in this weblog entry. Notice that I picked a small radius of 25 miles yet the illustration clearly shows a lot of activity. Had I picked a larger radius, say 50 miles, the graphic would show many more storms ( for an example of what I mean, see illustration D with a 100 mile radius centered on Inverness).
– ILLUSTRATION H –
Note: If you would like to utilize the program I used to derive illustration D and illustration H, here is a link:
http://csc.noaa.gov/hurricanes/#
The Relationship Between Wind Velocity and Its Potential Force
There is one last point I’d like to make and I have found in my years of teaching that there are many people who do not know this: One would think that the potential force of an 80 mph wind would be twice that of a 40 mph wind. But that is not true. The relationship is not linear – it is exponential. An 80 mph wind has FOUR TIMES the potential force of a 40 mph wind. When someone looking at the historical chart above sees mostly tropical storms (green) and category 1 hurricanes (yellow) they typically tend to minimize the dangers. They don’t realize that an 80 mph category 1 hurricane wind is far worse than a 60 mph tropical storm wind. I’ve done the math and, as it turns out, an 80 mph hurricane wind has 1.78 times the potential force of a 60 mph tropical storm wind (or close to twice the potential force). So, in even more simple terms, small increases in wind velocity result in large increases in potential force! For more discussion on the relationship between velocity and force, click on this link to a previous weblog entry:
Wrap-up
My next mission is to discuss this with some people in the area to learn their attitudes and feelings on the subject. I’m sure I will learn a lot and gain more knowledge and insight. For example, I’ll bet there are some who just don’t feel it’s worth the effort – that they will just evacuate and let insurance take care of things, or maybe take some losses and leave for good if a serious storm messes things up. Others must find permanent window and door protection to be “cost prohibitive” and have plans to somehow temporarily protect those openings – maybe at the last minute. None of those approaches work for me; there are just too many variables. For example, try buying plywood when it becomes fairly clear that a hurricane is coming your way. Or – consider what it might be like if you do plan to evacuate but wait too long and are unable to do so. Being inside a home that is breaking apart during a serious hurricane is no picnic.
NOTE: See link below to “Window Protection Is Essential”.
I suspect that there are many who feel they have thought things through and that their apparent inaction is merely a function of our individual differences in thinking. Perhaps they do indeed have a “plan” albeit different than mine. What’s the saying – “Different strokes for different folks”? Regardless, I strongly recommend advanced preparation.
The complacency I’m talking about is defined at Dictionary.com as “a feeling of quiet pleasure or security, often while unaware of some potential danger, defect, or the like.” I observed complacency among many people in pre-Andrew Homestead and suspect it exists there again because, after all, that was 22 years ago. So why should I expect a greater awareness and more obvious preparation along the Nature Coast where Citrus County is located? The fact is, I don’t. But I can dream, can’t I?
MORE INFORMATION:
Recent FEMA Release: http://www.fema.gov/news-release/2014/08/22/decade-after-2004-storms-fema-urges-hurricane-preparedness
Citrus County Emergency Management – http://www.sheriffcitrus.org/EM/
Disaster Preparedness (Florida Department of Health – Citrus County) http://www.floridahealth.gov/chdCitrus/disasterpreparedness.htm
Hurricane misconceptions: https://cloudman23.wordpress.com/2008/09/23/952/
Saffir-Simpson hurricane categories: http://www.nhc.noaa.gov/aboutsshws.php
Sustained winds: http://www.aoml.noaa.gov/hrd/tcfaq/D4.html
Window protection is essential: https://cloudman23.wordpress.com/2008/09/08/window-protection-for-hurricanes-is-essential/
The effects of hurricane winds upon a house: https://cloudman23.wordpress.com/2008/09/10/the-effect-of-hurricane-winds-upon-a-house/
Hurricane focus on Central Florida: https://cloudman23.wordpress.com/2008/09/13/hurricane-focus-on-central-florida/
Why is Florida so humid? https://cloudman23.wordpress.com/2009/07/04/why-is-florida-so-humid/
TROPICAL STORM LEE 5 DAY PRECIPITATION FORECAST – VALID 8am EDT SUNDAY
Thanks to the National Weather Service Hydrometeorological Prediction Center for this graphic.
What you see is a 5 day forecast for the total rainfall in inches between 8 AM Eastern Daylight Time Sunday and 8 AM EDT on Friday . The feared 15″ of rain in the New Orleans area predicted 36 hours earlier seems highly unlikely. For ease in reading, left click the image two times independently for full enlargement.
Lee Expected To Dump Lots Of Rain In the Next 5 Days!
Thanks to the National Weather Service Hydrometeorological Prediction Center for this graphic.
What you see is a prediction for the total rainfall in inches between 8 AM Eastern Daylight Time Saturday and 8 AM EDT on Thursday (in other words – a 5 day total forecast). Already, since this was released, the feared 15″ of rain in the New Orleans area seems highly unlikely due to dry air from Texas being drawn into the system. For ease in reading, left click the image two times independently for full enlargement.
DAY ONE OF HURRICANE SEASON IS INTERESTING!
Below is a “cut and paste” from the National Hurricane Center’s report for the first day of the hurricane season, 2011. There is a low pressure system in the Atlantic now making a beeline for my part of Florida and expected to be here around 1 PM. Item 1 below is the discussion of that system. At the very end of this posting you will find a link to the page from which this information was cut. If the graphic you first see is not the satellite image, just left click on it and it should change for you.
My daughter is visiting from New Mexico and this is the day that she and I were to have gone sailing. However – that activity has been canceled and my “little girl” is sleeping in. There was a time in my life when I was more daring and would have gone out anyway – working hard to strategically find safe shelter and counting on lots of luck. But now in my 72nd year I am one to err on the side a caution. The aluminum mast supported by a steel fore-stay and two steel shrouds all serve as excellent lightning attractors. I do not wish for my daughter (or myself for that matter) to become a “crispy critter.” The fun is not worth the risks. So we will find something else to do. The tiny red dot on the image below approximates where I live in Florida and the system is traveling toward the west-southwest. Left click on the image to enlarge.
From my point of view, this is a fitting “sign” that our hurricane season this year is likely to be a busy one. The post that follows this one will link you to a description of the NOAA summary of this years forecast.
ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 800 AM EDT WED JUN 1 2011 FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO... 1. A SMALL AREA OF LOW PRESSURE LOCATED ABOUT 200 MILES EAST OF JACKSONVILLE FLORIDA IS MOVING WEST-SOUTHWESTWARD AT AROUND 20 MPH. THE LOW CONTINUES TO PRODUCE A CONCENTRATED AREA OF SHOWERS AND THUNDERSTORMS...AND ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE FOR SOME DEVELOPMENT OF THIS SYSTEM BEFORE IT MOVES OVER NORTHERN FLORIDA LATER TODAY. REGARDLESS OF DEVELOPMENT...THIS DISTURBANCE COULD PRODUCE LOCALLY HEAVY RAINFALL AND STRONG GUSTY WINDS OVER PORTIONS OF THE FLORIDA PENINSULA. THERE IS A MEDIUM CHANCE...30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. FOR ADDITIONAL INFORMATION ON THIS SYSTEM...PLEASE SEE PRODUCTS FROM YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE. ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS. TODAY MARKS THE FIRST DAY OF THE ATLANTIC HURRICANE SEASON...WHICH WILL RUN UNTIL NOVEMBER 30. LONG-TERM AVERAGES FOR THE NUMBER OF NAMED STORMS...HURRICANES...AND MAJOR HURRICANES ARE 11...6...AND 2...RESPECTIVELY. THE LIST OF NAMES FOR 2011 IS AS FOLLOWS: NAME PRONUNCIATION NAME PRONUNCIATION ------------------------------------------------------------- ARLENE AR LEEN- LEE LEE BRET BRET MARIA MUH REE- UH CINDY SIN- DEE NATE NAIT DON DAHN OPHELIA O FEEL- YA EMILY EH- MIH LEE PHILIPPE FEE LEEP- FRANKLIN FRANK- LIN RINA REE- NUH GERT GERT SEAN SHAWN HARVEY HAR- VEE TAMMY TAM- EE IRENE EYE REEN- VINCE VINSS JOSE HO ZAY- WHITNEY WHIT- NEE KATIA KA TEE- AH THIS PRODUCT...THE TROPICAL WEATHER OUTLOOK...BRIEFLY DESCRIBES SIGNIFICANT AREAS OF DISTURBED WEATHER AND THEIR POTENTIAL FOR TROPICAL CYCLONE FORMATION DURING THE NEXT 48 HOURS. THE ISSUANCE TIMES OF THIS PRODUCT ARE 2 AM...8 AM...2 PM...AND 8 PM EDT. AFTER THE CHANGE TO STANDARD TIME IN NOVEMBER...THE ISSUANCE TIMES ARE 1 AM...7 AM...1 PM...AND 7 PM EST. A SPECIAL TROPICAL WEATHER OUTLOOK WILL BE ISSUED TO PROVIDE UPDATES ...AS NECESSARY...IN BETWEEN THE REGULARLY SCHEDULED ISSUANCES OF THE TROPICAL WEATHER OUTLOOK. SPECIAL TROPICAL WEATHER OUTLOOKS WILL BE ISSUED UNDER THE SAME WMO AND AWIPS HEADERS AS THE REGULAR TROPICAL WEATHER OUTLOOKS. A STANDARD PACKAGE OF PRODUCTS...CONSISTING OF THE TROPICAL CYCLONE PUBLIC ADVISORY...THE FORECAST/ADVISORY...THE CYCLONE DISCUSSION... AND A WIND SPEED PROBABILITY PRODUCT...IS ISSUED EVERY SIX HOURS FOR ALL ONGOING TROPICAL CYCLONES. IN ADDITION...A SPECIAL ADVISORY PACKAGE MAY BE ISSUED AT ANY TIME TO ADVISE OF SIGNIFICANT UNEXPECTED CHANGES OR TO MODIFY WATCHES OR WARNINGS. THE TROPICAL CYCLONE UPDATE IS A BRIEF STATEMENT TO INFORM OF SIGNIFICANT CHANGES IN A TROPICAL CYCLONE OR TO POST OR CANCEL WATCHES OR WARNINGS. IT IS USED IN LIEU OF OR TO PRECEDE THE ISSUANCE OF A SPECIAL ADVISORY PACKAGE. TROPICAL CYCLONE UPDATES ...WHICH CAN BE ISSUED AT ANY TIME...CAN BE FOUND UNDER WMO HEADER WTNT61-65 KNHC...AND UNDER AWIPS HEADER MIATCUAT1-5. ALL NATIONAL HURRICANE CENTER TEXT AND GRAPHICAL PRODUCTS ARE AVAILABLE ON THE WEB AT WWW.HURRICANES.GOV. SIGN UP FOR PRODUCT UPDATES BY EMAIL AT WWW.HURRICANES.GOV/SIGNUP.SHTML...IN ALL LOWER CASE. YOU CAN ALSO INTERACT WITH US ON FACEBOOK AT WWW.FACEBOOK.COM/US.NOAA.NATIONALHURRICANECENTER.GOV. $$ FORECASTER BERG/PASCH NNNN Here is a link to the National Hurricane Center Home Page: http://www.nhc.noaa.gov/gtwo_atl.shtml
The Hurricane Season for 2011 Has Begun
By the time you read this, May of 2011 will have ended and the Northern Hemisphere Atlantic, Caribbean, and Gulf of Mexico hurricane season will have begun. The following link will take you to a summary of the NOAA outlook for this season:
http://www.noaanews.noaa.gov/stories2011/20110519_atlantichurricaneoutlook.html
Please be prepared if you live in hurricane territory.
The loop above illustrates nicely that a tropical system does not have to be a hurricane in order to cause significant problems including fatalities. TO ACTIVATE YOU MUST LEFT CLICK ON THE IMAGE. Here is what Wikipedia has to say about the 2008 storm: Tropical Storm Fay was a tropical storm and the sixth named storm of the 2008 Atlantic hurricane season. Fay formed from a vigorous tropical wave on August 15 over the Dominican Republic. It passed over the island of Hispaniola, into the Gulf of Gonâve, across the island of Cuba, and made landfall on the Florida Keys late in the afternoon of August 18 before veering into the Gulf of Mexico. It again made landfall near Naples, Florida, in the early hours of August 19 and progressed northeast through the Florida peninsula, emerging into the Atlantic Ocean near Melbourne on August 20. Extensive flooding took place in parts of Florida as a result of its slow movement. On August 21, it made landfall again near New Smyrna Beach, Florida, moving due west across the Panhandle, crossing Gainesville and Panama City, Florida. As it zigzagged from water to land, it became the first storm in recorded history to make landfall in Florida four times. Thirty-six deaths were blamed on Fay. The storm also resulted in one of the most prolific tropical cyclone related tornado outbreaks on record. A total of 81 tornadoes touched down across five states, three of which were rated as EF2. Damage from Fay was heavy, estimated at $560 million.
Here is a link to Wikipedia’s coverage of that storm:
http://en.wikipedia.org/wiki/Tropical_Storm_Fay_%282008%29
Here is a link to my list of 23 Misconceptions About Hurricanes:
http://ztechzone.net/learningzone/science/science55/hurricanes.html
Pilot Error May Have Caused Crash Near Buffalo
What so many have been reluctant to say – probably being extra cautious because nothing is certain at this time – was finally printed in yesterday’s Wall Street Journal. In my first posting about this terrible aircraft accident I suggested that if icing was indeed the problem – the accident should never have occurred. Now – it is beginning to look as though the “reaction” to icing might have been incorrect causing the aircraft to immediately stall.
Please be mindful of the fact that the investigation of this accident is still in a very early stage. Here is a link to the WSJ article:
http://online.wsj.com/article/SB123492905826906821.html
If you wish to see other posts on this weblog but are unable, please click on the “blog” tab near the top of this page.
Icing Once Again Is Primary Suspect in Bombardier Dash 8 Q400 Crash
The cause of last Thursday’s terrible airplane crash near Buffalo, New York may never be know for sure. In any case, such investigations take many months. There was a brief period of time when there were some significant doubts as to the role of icing in the accident – partly due to the embryonic stage of the investigation hindered by the complexities of carefully sorting debris of the aircraft and the house from the remains of the victims. What a difficult job that must be.
Yesterday and today there have been more indications that icing was responsible. If anything accurate can be said about the nature of the environment which produces icing conditions it is that it is fickle. Just as the surface has its own micro-climatology, so do clouds. It appears to me that the plane that crashed must have entered an icing environment which might have been severe. There is also a possibility of some form of mechanical and/or instrument failure. The final determination could very well point to a combination of unfortunate happenings.
If you wish to see other posts on this weblog but are unable, please click on the “blog” tab near the top of this page.
ICING AS PART OF THE HYDROLOGIC CYCLE – SOME BASICS
THE HYDROLOGIC CYCLE, A CLASSICAL TOPIC
IN NATURAL SCIENCE COURSES
I’ve taught the hydrologic cycle many times in geology, meteorology, physical oceanography and environmental science classes. It’s always been a pleasure but I’ve never had enough time. All of these were college courses and in almost every case the text book covered the subject adequately. However, the manner in which water moves and changes in our natural environment is so very interesting that a few pages in a text with a traditional drawing and an hour lecture from me simply does not do the subject justice. Water is such a remarkable compound – I can’t find the words to explain how very interesting it is and how mysterious it can be at times considering the amount of scientific attention it has received through the years. There is still so much to learn.
So, it is with excitement that I look forward to a 6-hour course that I am scheduled to teach in May to the Senior Institute enrollees at Central Florida Community College. In 37 years of full-time college teaching (and 4 years part-time) I never had the opportunity to devote so much time to the subject. The method I intend to use is my own “idea” but surely it has been done before – that is, to follow water step-by-step as it goes from one phase or one environment to the next. My presentation won’t be a journey without side trips and backtracking. There are multiple manners in which water can transform and/or move with interesting little anomalies along the way. With 6 hours to utilize I will be able to discuss aspects that were only fleetingly mentioned in my previous hour-long presentations e.g.: Capillary action, deposition, glacial calving, influent groundwater movement, juvenile water, super-cooled droplets, and much more.
SUPERCOOLED CLOUD DROPLETS AND ICING
I feel fairly certain that some people who read this have had the experience of having rain freeze upon impact with their vehicle’s windshield. Some would assume that the freezing occurs because the windshield is so very cold. That is usually not the case. Instead, the liquid droplets were probably at a temperature well below “freezing” and the impact with the windshield itself triggered the instant freezing. Hopefully, the “defrosting” vents can keep the windshield warm enough so that the ice can be quickly cleared. Now, imagine what it must be like if the surfaces being iced are the windshield and wings of your aircraft in flight – as well as other aircraft surfaces (e.g. propellers, fuselage, horizontal stabilizers)!
Today, February 15, 2009, the mere thought of super-cooled droplets hauntingly reminds me that in addition to the marvelous beauty of water’s multifaceted journeys and transitions through our natural environment, there are some insidious elements that can become deadly in this modern world. Of course, I’m thinking specifically of the recent terrible aircraft accident responsible for 50 fatalities near Buffalo, New York.
PURE SPECULATION
For a short while since the accident it appeared that icing might have been the culprit or perhaps a contributing factor in causing the aircraft to make its sudden rapid descent (apparently almost immediately after the application of flaps). At the time other aircraft in the vicinity were reporting icing. HOWEVER, AT THE TIME OF THIS WRITING, NEWS RELEASES HAVE INDICATED THAT THE NATIONAL TRANSPORTATION SAFETY BOARD CLAIMS THAT ICING APPEARS NOT TO HAVE BEEN A FACTOR. The changing of the airfoil’s shape upon flap engagement might have triggered the rapid descent – an apparent stall leading to a flat spin. That would indicate either insufficient air speed at the time of flap deployment or some type of catastrophic failure. SINCE MANY AVIATION ACCIDENTS HAVE BEEN CAUSED BY ICING – AND IT WILL REMAIN A PROBLEM FOR AIRCRAFT FOR A LONG TIME TO COME, I SHALL CONTINUE.
When icing was being blamed, I suspected that some critical errors might have been made in the cockpit. At best, my notions were intuitive – or, on the other end of the spectrum, unfair during such an early stage in the investigation. Nevertheless, a surprising amount of information has been made available during this embryonic phase – partly due to the fact that the flight recorders are advanced models and they were in very good shape. There is no need for me to dwell on factors that can cause a plane to become unstable when icing occurs – suffice it to say that airfoils lose “lift efficiency” quickly when ice buildup changes their shape and of course the weight of the ice accumulation can also be a huge factor. I do not know what kind of air speed indicators are installed on that type of aircraft but I do know that icing can cause false readings on some types. Icing can also cause problems at air intakes and oil cooler intakes of some aircraft.
BUT WHY DOES THE PHENOMENON OCCUR
IN THE FIRST PLACE?
The cause of the icing is a surprise to most people. Though icing can occur on a plane’s very cold surface when it descends into “warm” clouds whose temperatures are above freezing, the vast amount of problematic icing occurs when the liquid droplets themselves are below what we traditionally consider freezing temperature. These droplets consist of what is called supercooled liquid water (SLW). Water in cloud droplets can get as cold as about negative 40 degrees Celsius (which is the same as negative 40 Fahrenheit) without freezing.
When liquid water freezes (box 3 to 4 in the illustration above) the water molecules align in a crystalline fashion. But in order to do so they need one of two things: 1) either a freezing nuclei whose surface acts as a template to initially “show” the molecules how to (or trigger the molecules to) line up, or 2) some molecules themselves must be jolted (or jiggled) such that for at least an instant they are arranged so they can act as a template or model for the rest to follow. The likelihood of such alignment occurring in undisturbed droplets is slim. This would not be true of most fresh water at the surface, such as in lakes because there are microscopically-sized particles available in the water to act as templates. On the other hand, water that has condensed and remains in the air is very “clean” by comparison.
An aircraft flying though supercooled cloud droplets causes considerable rapid stirring to set the stages for freezing upon impact with that aircraft – just as supercooled raindrops freeze upon impact with trees and suspended wires in those notorious, damaging ice storms.
VIDEO DEMONSTRATIONS
The first three links below show convincing demonstrations of liquid water freezing as a result of hexagonal ice crystal seeding. The ice crystals provide the template which “shows” the liquid water what to do in order to become solid. In the third example when the water freezes and builds up a small mound on the wooden post, I suspect that the split second ideal alignment of some water molecules (while pouring) provoked the freezing.
http://www.youtube.com/watch?v=Xe8vJrIvDQM
http://www.youtube.com/watch?v=gGpNhBPYNfs
http://www.youtube.com/watch?v=4g1BDpU7ZQo
In this 4th example you will see that a jolt causing a sloshing of the water in the small amount of air space at the top of the bottle allows for enough water movement so that for an instant a hexagonal orientation occurs among some molecules causing a very rapid “follow the leader” freezing all the way down to the bottom of the bottle.
http://www.youtube.com/watch?v=DpiUZI_3o8s
Just as condensation and deposition give off heat, freezing is also exothermic. This is probably why some of the water remains in the liquid state. If the SLW is not very much colder than “freezing” temperature, the heat given off during freezing will cause the remaining liquid to acquire enough heat to teeter over to the liquid side.
Use the search term “supercooled water” on YouTube.com and you will find many other video demonstrations.
WHEN WATER FREEZES IT EXPANDS, BECOMING LESS DENSE. THIS EXPLAINS WHY SOLID WATER FLOATS UPON LIQUID WATER.
If you compare box 3 and 4 in the illustration in this post, you will see why water expands and becomes less dense upon freezing. To establish the hexagonal grid necessary for ice, the molecules can’t be as close together as they were when they were in the cold liquid stage.
Information on supercooled liquid water would have eventually been posted here if the Continental Express Flight 3407 disaster had not occurred. It is regrettable that the accident played a role in my posting this information at this time. I offer my sympathy to all who have broken hearts over the loss of a loved one and all others adversely effected.
Finally, the information in this post about SLW and icing merely scratches the surface compared to that which is known. But, that which is not understood is formidable.