Hector: Thunderstorms over the Tiwi Islands in the Maritime Continent

Introduction

Hector from Gunn Point, Northern Territory

Three articles involving the thunderstorm phenomenon known as Hector were investigated. These storms take place over the Tiwi Islands, which are located approximately 80 km north of Darwin, Australia, during monsoon transition periods (November to December and February to March). Since the islands (Bathurst to the west and Melville to the east) are only separated by a narrow channel (Apsley Strait), they are treated as a single island in all three studies (see Figure 1, Beringer, et al.) and the total dimensions are approximately 150 km east to west and 60 km north to south.

Figure 1

Two of the articles attempted to describe and classify the thunderstorms themselves. Beringer, et al. used satellite imagery and soundings from the Darwin airport while Crook used linear and nonlinear models. The third article used data from the Maritime Continent Thunderstorm Experiment (MCTEX) to describe the diurnal cycle of the boundary layer.

All three articles recognized the existence of two wind regimes and also noted various modes of development or non-development. Only Beringer, et al. related the importance of Hector to the global climate: “[T]he Tiwi Islands heat the atmosphere from below…result[ing] in convective towers that penetrate upward carrying latent heat into the upper troposphere…resulting in the transport of heat and moisture that provides a meridional energy balance” by driving the Hadley and Walker circulations which are “vital to global atmospheric circulation.” (Beringer, et al., p. 1022) The other two studies focus very narrowly on the Tiwi Islands, never mentioning global implications.

Methods

All three studies took advantage of data from MCTEX, which was conducted in November and December of 1995, and an earlier experiment, the Island Thunderstorm Experiment (ITEX), that was conducted in 1988 and 1989. Schafer, et al. made extensive use of the MCTEX data to describe the boundary layer while Crook and Beringer, et al. relied on the same data for initialization and validation. All three studies compared and contrasted their results with ITEX data.

Beringer, et al. used infrared images from the Japanese Geostationary Meteorological Satellite between 0700 and 1800 local time (all times will be reported in local time which is UTC + 9.5 hours). They also took advantage of the 0730 radiosonde soundings at the Darwin airport. From these two sources they determined convective available potential energy (CAPE), precipitable water (PW), wind shear at the 600 hPa level, surface and 700 hPa wind speeds, convective inhibition (CIN) and the bulk Richardson number (BRICH). These values were used to sort 55 unambiguous event days (which were also not complicated by widespread oceanic convection) into four modes: Hector, suppressed Hector, no Hector, and late developing Hector.

While Beringer, et al. relied on soundings from the Darwin airport, Schafer, et al. took advantage of a comparatively dense network of sensors on Bathurst and Melville Islands. This network consisted of 15 automatic weather stations, three boundary layer wind profilers (levels of  every 100 m up to 2000 m and every 300 m up to 20 km), radiosonde launches every two hours at one location, a Doppler weather radar, a remotely controlled aircraft (aerosonde) and two all sky cameras. These observations were used to determine horizontal winds, mean virtual potential temperature, boundary layer depth, air temperature, and convergence. Horizontal and vertical variations of these descriptors were used to characterize the development of the boundary layer.

Rather than collecting or interpreting data, Crook used a linear and a nonlinear model to approximate the environment. The microphysics, topography and island shape were held constant in both models. Five parameters (surface wind speed, surface wind direction, surface flux of moisture, surface flux of heat and low-level moisture) were varied and each case was compared to a control experiment. Typical values for the control experiment (as well as a typical wind profile) were derived from MCTEX data.

Wind Regimes

All three studies recognized the existence of two dominant wind regimes. The east to northeasterly regime resulted in development on the western side while the west to southwesterly regime resulted in development on the eastern side. Beringer, et al. found a majority of the 55 cases they studied were in the easterly group while Schafer, et al. had eight cases in the easterly group and nine cases in the westerly group. Crook used only the westerly regime in his studies and demonstrated that convection was favored when winds were parallel to the major axis of the island. Only Beringer, et al. argued that storms in easterly flow had a larger areal extent (consistent with an earlier study: Down Under Doppler and Electricity Experiment) while storms in westerly flow had greater vertical development (as evidenced by -700 C cloud top temperatures instead of -600 C). This was explained by enhanced convection in the westerly regime due to advection of moist oceanic air over land.

Modes

Crook offers a good discussion of the historical understanding of Hector. Prior to MCTEX, it was hypothesized that sea breeze convergence over the island was the main trigger for convection. MCTEX demonstrated that sea breezes seldom collided. This led to a new explanation with two modes of development. The most common (80% of Hector events) is due to the collision of one of the sea breeze fronts with an evaporatively produced cold pool and is termed “type B”. This is similar to the “Hector” mode described by Beringer, et al., but also seems to lump the mode Beringer, et al. terms “suppressed Hector” into the same group. 36 out of 42 storm events studied by Beringer, et al. were either determined to be in the Hector mode or the suppressed Hector mode. This gives a frequency of 70%, very similar to the 80% mentioned by Crook.

The other 20% of events were “type A” according to Crook (who takes his categorization from a 2000 paper by Carbone, et al.). Type A Hectors owe their convergence to the collision of the two sea breeze fronts. This is analogous to the “late developing Hector” mode described by Beringer, et al. 14 of 46 or 30% of developments were determined to be late developing. Although Schafer, et al. were studying boundary layer development rather than the development of the actual Hector events, they also described a difference between early (type B after Crook and Hector/suppressed Hector after Beringer, et al.) and late (type A after Crook and late developing Hector after Beringer, et al.) developing events. They noted specifically that storms occurring after 1330 had a better developed boundary layer (~2 km deep) while storms occurring prior to 1330 had a shallower boundary layer (~1.5 km).

Based on Crook’s nonlinear moist model runs, he determines that low-level moisture (represented in his Figure 2 – originally Crook’s Figure 15 – by CAPE) is the primary factor in determining which mode will occur. From this figure, it can be seen that large CAPE results in type B development while small to moderate CAPE results in type A development. Beringer, et al. did not rely on a single parameter but rather the combination of low-level moisture (CAPE), CIN and shear (whereas Crook used a constant shear based on MCTEX data and does not consider CIN). They conclude (as is summarized in Table I) that large CAPE combined with large shear and large CIN lead to type A or late developing Hector. This contradicts Crook’s conclusion.

Figure 2. Total condensate against time for simulations with upstream CAPEs of 1000, 1500, and 3000 J/kg. All measures are normalized by the maximum value from the control experiment.

Figure 2. Total condensate against time for simulations with upstream CAPEs of 1000, 1500, and 3000 J/kg. All measures are normalized by the maximum value from the control experiment.

What is conspicuous about Table I, however, are the large standard deviations, especially for CAPE. Schaefer, et al. found that variability in boundary layer characteristics was minimized when sea breezes are most active, between 1000 and 1400. This helps to explain the large variability in Table I since 0730 soundings were used.

Table 1

Unique Findings of Each Study

Up to now, the overlapping areas of each study have been examined for similarities and differences. This analysis could only be carried so far since each study had its own unique objective. Exciting findings from each paper that do not necessarily overlap with the other two will now be discussed.

    • Evolution of maritime continent thunderstorms under varying meteorological conditions over the Tiwi Islands (Beringer, et al.)

      This study was the only one concerned with conditions leading to the most rare situation, the non-Hector. Beringer, et al. first discuss the suppressed Hector development mode, which is most likely due to suppression by pre-existing convection from a squall line moving through the area consuming CAPE. Although the non-Hector mode is also characterized by low CAPE, the presence of large shear (as opposed to small shear in the suppressed Hector development mode) indicates a different mechanism is responsible for this mode than for the suppressed Hector mode. Two proposed explanations were (1) mid-level subsidence combined with advection of dry continental air over the islands and (2) existence of residual cloudiness from previous deep convective activity over the ocean.

    • Understanding Hector: The dynamics of island thunderstorms (Crook)

      Upon recognizing that a majority of Hector events are not due to convergence of the two sea breezes, Crook proposes that perhaps a peninsula will produce the same results as an island. For the linear case, rainwater decreases by a factor of approximately two when a peninsula is used. For the nonlinear case, very little convection occurs over the peninsula (which has the northern Tiwi Islands coastline). From this he concludes that although sea breeze convergence is not the primary mechanism, interaction between the sea breezes and cold pools is enhanced by the proximity of the two coastlines and thus that an isolated heat source is a necessary condition for the Hector convective system.

    • Boundary layer development over a tropical island during the Maritime Continent Thunderstorm Experiment (Schafer, et al.)

      As mentioned previously, the first two papers are similar in that they strive to classify the Hector thunderstorm event. This paper practically ignores the thunderstorm events while it focuses on the development of the boundary layer throughout the diurnal cycle. Because of this, it was the only study to investigate the overnight environment and to describe what happens to reset it such that development can occur again the next day.  After sunset, a surface-based temperature inversion forms. A remnant mixed layer persists over the surface inversion until it is replaced by advection of an oceanic mixed layer over the island. Without this oceanic mixed layer, convection for the following day would be suppressed.

Summary

The three articles discussed took very different approaches to the same phenomenon. Beringer, et al. used available data (satellite images and airport soundings) to study the different wind regimes and development modes of Hector thunderstorms over the Tiwi Islands. From the reader’s standpoint, this was the best paper by far since it emphasized the importance of understanding Hector to making more accurate global predictions.

Crook approached the problem dynamically by applying linear and nonlinear models. In this manner, he was able to limit variability to one parameter at a time in order to investigate its effect on convection. Although conclusions about the different modes of Hector did not agree exactly with Beringer, et al., the importance of low-level moisture content was demonstrated. One of the main shortcomings of this study was the failure to investigate the easterly wind regime.

The most expensive of the three studies was certainly Schafer, et al. since it relied almost solely on data collected in situ with multiple sensors (rather than taking advantage of previously collected data sets). This paper was also the most difficult to compare and contrast with the other two since it focused on boundary layer development rather than the thunderstorms themselves. An important conclusion was the resetting of the mixed layer by oceanic air.

References

Beringer, J., N. J. Tapper, and T. D. Keenan, 2001: Evolution of maritime continent thunderstorms under varying meteorological conditions over the Tiwi Islands. Int. J. Climatol., 21, 1021-1036.

Crook, N. A., 2001: Understanding Hector: The dynamics of island thunderstorms. Mon. Wea. Rev., 129, 1550-1563.

Schafer, R., P. T. May, T. D. Keenan, K. McGuffie, W. L. Ecklund, P. E. Johnston, and K. S. Gage, 2001: Boundary layer development over a tropical island during the Maritime Continent Thunderstorm Experiment. J. Atmos. Sci., 58, 2163-2179.

Jack’s Common Core Subtraction Problem: Not So Hard After All

DISCLAIMER:  I have no children in public school nor am I a public school teacher. That said, I am no fan of Common Core (and especially not of its implementation).  I find it unfortunate, however, that people are so quick to point out how bad certain Common Core math problems are without looking at what the correct answer should actually be.  Take, for example, this math problem which has been in the news lately: common core subtraction I know this will be hard, but let’s assume for a moment that you don’t know much about subtraction and especially don’t know about things like borrowing (at least that’s what we used to call it back in the day).  While the above problem does NOT require borrowing, it’s setting us up to be able to understand how borrowing will eventually work. So what did Jack do wrong?  The goal here was to start with the first number (427), then count backwards on the number line using each place of the smaller number (316) from largest to smallest (i.e. from the hundreds place to the ones place).  Jack started by going from 427 to 327 to 227 to 127, so he expertly handled the hundreds.  Next, he needed to account for the tens place.  This is what he missed.  He should have gone from 127 to 117.  Finally, he should account for the ones place by going from 117 to 116 to 115 to 114 to 113 to 112 to 111. Why is this kind of reasoning important?  Remember, we don’t know anything about “borrowing.”  Now, instead of subtracting 316 from 427, let’s say we want to subtract 327 from 416 (416 – 327 = ?).  Using the exact same method: Go down by three hundreds – 416 to 316 to 216 to 116 Go down by two tens – 116 to 106 to 96 Go down by seven ones – 96 to 95 to 94 to 93 to 92 to 91 to 90 to 89 So without having to grasp the abstract concept of borrowing, we find that 416 – 327 = 89. Again, I’m no public school teacher, but having taught arithmetic, pre-algebra, algebra, statistics and pre-calculus at the post-secondary level, I can tell you that it’s definitely easier to get student buy-in to abstract notions like carrying and borrowing when they have demonstrated for themselves using the number line that these shortcuts do, in fact, give the correct answer. It’s OK to dislike Common Core, but you only look ignorant when you call out problems like the one above without addressing what the correct solution is and how you think the concept should be taught differently.

Everyone Has A’s! A’s! A’s! A’s!

This past semester, I took an undergraduate course for the first time in nearly 20 years.  I enrolled in Physical Anthropology (ANTH 102) at San Diego City College as the first step toward my goal of becoming a nautical archaeologist.  I didn’t know what to expect, but I certainly didn’t expect such a lax grading policy for a class that qualifies as one of only two science courses required to earn a bachelor’s degree in California.

A total of 600 points were possible for the class.  300 of those came from three projects, each of which took about four hours to complete.  The first project required a visit to the San Diego Museum of Man (mine is here).  The second required online research of various primates or a trip to the San Diego Zoo (click here for my zoo project).  The final “creativity” project was a presentation of literally anything having to do with anthropology (my project is here).  One student baked cookies and wrote various vocabulary words on them.  Another held up a picture book of Disney’s Tarzan and talked about how much he enjoyed reading it to his son.  From what I could tell (based on a quick glance at the professor’s grade spreadsheet when she was showing me my own scores), grading for these projects was binary; students either received 100/100 points for turning them in or 0/100 points for not turning them in.

The other 300 points were based on the best three of four multiple choice tests.  There was no final exam.  Additionally, 25 extra credit points were awarded for attendance at a one-day anthropology conference and, when test scores were abysmally low, another 25 points were awarded for writing a one-page review of any movie having anything to do with anthropology (one student wrote about Ice Age).

This grading policy meant that by simply completing the three projects, students already had 300/600 points (350/600 if they did both extra credit “assignments”).  In order to get a C in the class, a student who did both extra credit assignments would only need an additional 70 points from all three tests.  That’s an average grade on each test of 23.3%!

You read that correctly.  My classmates could get credit for one of their two required science classes by answering less than one-quarter of the multiple choice test questions correctly.

Here’s how it breaks down with and without extra credit for each grade:

Average test score needed to get a(n):    A          B          C

With no extra credit assignments:          80         60        40

With one extra credit assignment:          71.7      51.7      31.7

With both extra credit assignments:        63.3      43.3      23.3

That’s right.  Students who completed both extra credit assignments could score an average of 63.3% (barely a D) on their three highest tests (remember, the lowest score was dropped) and still get an A in this science class.

America, you have been warned.  This is your future.

But for now, everyone has A’s! A’s! A’s! A’s!

Noah’s Flood – Probably Real, Probably Caused By Climate Change, and Probably NOT Due To Anthropogenic Global Warming

Last month, I noticed several articles mocking Republican Congressman Joe Barton for citing the Biblical “Great Flood” as an example of climate change not caused by man:

“I would point out that people like me who support hydrocarbon development don’t deny that climate is changing,” he added. “I think you can have an honest difference of opinion of what’s causing that change without automatically being either all in that’s all because of mankind or it’s all just natural. I think there’s a divergence of evidence.”

“I would point out that if you’re a believer in the Bible, one would have to say the Great Flood is an example of climate change and that certainly wasn’t because mankind had overdeveloped hydrocarbon energy.”

Notice especially some of the comments from “Top Commenters” who mock Congressman Barton:

Oh yeah and to hell with what all those stupid scientists have learned through their years and years of extensive research, those idiots don’t know nothin’. YAY JESUS! -Dave Fox

 

Thanks for sharing Tim….I feel much dumber now for having read that….LOL.  What a douche! -Patrick Salyard

 

RUBE. -Lawrence Edward Martin

What many of those commenters (and perhaps even Congressman Barton) don’t know is that the Great Flood story is not unique to the Bible.  The most similar flood story appears in the Epic of Gilgamesh, with Utnapishtim taking the same role as Noah.  Encouraged by the ubiquity of the flood myth, geologists William Ryan and Walter Pittman hypothesized that such a flood actually occurred.  They concluded it was due to the bursting of a natural dam in the Bosporus around 5600 B.C. as sea level rose in the Mediterranean (sea levels were rising as global temperatures rose and continental ice sheets melted).   In 1997, they published the book Noah’s Flood, which not only looked at the similarities between the biblical story of Noah and the tale of Utnapishtim, but also looked at information like genetic data, geologic samples and the language diaspora away from the Black Sea to support their theory.

But does the fact that two geologists from Columbia University wrote a book supporting the idea that the flood actually happened mean Congressman Barton is not, in fact, a “douche” and a “rube” when it comes to anthropogenic global warming?  Perhaps William Ryan and Walter Pittman are also douches and rubes.  If that is the case, their douchiness and rubery is quite advanced; this past December, Robert Ballard (the same Robert Ballard who found the Titanic) started looking for evidence of the settlements which should have once existed around the fresh water lake at what is now the deepest part of the Black Sea (if Ryan and Pittman are correct).  His initial survey did not find anything, but he plans on returning this summer.  It would seem, at least for the moment, that science has come down in support of Congressman Barton.  Earth’s climate is capable of changing of its own accord, even catastrophically.  Sometimes those changes are so catastrophic they take on an epic (one might even be tempted to say “biblical”) quality in the retelling.

Safety and Rumors

By now I am used to receiving emails from my son’s school with spelling and grammar errors as well as factually incorrect information, but this one was just downright confounding for its utter lack of substance:

Subject:  Safety and Rumors

Good evening, this is a message from [school name redacted] High Administration.

We are contacting you about a number of rumors that have been circulating among our students about something bad happening on our campus. We can assure that these are all rumors. Our school police have followed up on all leads that have come to us and have found nothing credible. You and your children are safe here at [name redacted] High School and we will continue to follow up on any information that comes to us. We have a vacation just around the corner and we expect to see everyone here tomorrow. Thank you.

After reading it, I was more worried than if I had never gotten an email to begin with.  What rumors?  I hadn’t heard any rumors.  My son hadn’t heard any rumors.  What’s going on?  Then I remembered… Fleetwood Mac is playing in Anaheim tonight.  Given their track record, the school probably just forgot the “u” in Rumours.

Ferris Bueller Is Doctor Who

Versions of the Doctor

My kid “proved” this to me while we were stopped at a traffic light:

Ferris Bueller was portrayed in the film Ferris Bueller’s Day Off by Matthew Broderick.

Matthew Broderick voices Simba as an adult in Disney’s The Lion King.

The Lion King is a retelling of Shakespeare’s Hamlet (with Simba as Hamlet).

Hamlet was portrayed both on stage and on screen by David Tennant.

David Tennant took on the role of the Tenth Doctor in 2005.

Q.E.D.

Doctor Who Singing Twist and Shout:

An Excess of Irony

About two weeks ago, an act that has been referred to as “excessive celebration” kept Columbus (Texas) High School’s 4 x 100 relay team from qualifying for the state championships.


Since that time, the media has made much of the fact that the disqualifying gesture was an “act of faith” and has used this to tease their stories and color their interviews.  The disqualification was not made because the student displayed his faith, but rather because he made a display at all.  The fact that raising his index finger next to his ear (or perhaps raising his hand over his head; think “we’re number one!”) is considered “excessive” is the issue, not “freedom of religion.”

Here’s the official press release from the governing body of the track meet:

At the Region IV Conference 3A Track & Field regional meet held on Saturday, April 27 at Texas A&M Kingsville, a relay team from Columbus High School was disqualified by local meet officials for an unsporting act at the conclusion of the boys 4 x 100 meter relay. 

The meet official indicated the athlete crossed the finish line and gestured upward with his arm and finger and behaved disrespectfully toward meet officials, in their opinion. In the judgment of the official, this was a violation of NFHS track & field rule 4-6-1.  The regional meet referee concurred with this decision and the student was subsequently disqualified. There is no indication that the decision was made because of any religious expression. This was a judgment call, as are many decisions of meet officials in all activities.

According to NFHS rules, once the meet is concluded, the results become final. Neither the UIL nor NFHS have rules that prohibit religious expression.

The UIL takes situations such as these very seriously, and is continuing to investigate the matter fully.

It makes sense to call out the meet official on his or her seemingly ironic use of the word “excessive.”  What does not make sense is to turn this into an issue of religious freedom.  The only person who knows why he raised his hand and index finger toward the sky is the student who got disqualified, Derrick Hayes, and he has wisely chosen to remain silent on the issue.