Are there more hurricanes nowadays?

Hurricane Ian approaches Florida (NOAA image)

Florida is counting the cost of Hurricane Ian (above). While we empathise with the people affected by this terrible tragedy, and wish them well, it’s appropriate for a science blog to reflect on what’s happening. The paper “Trends in Global Tropical Cyclone Activity: 1990–2021” by Philip J. Klotzbach, Kimberly M. Wood, Carl J. Schreck III, Steven G. Bowen, Christina M. Patricola, and Michael M. Bell (Geophysical Research Letters, 14 March 2022) is a good guide.

Klotzbach et al. find that global hurricane counts have in fact decreased since 1990. We are not seeing more hurricanes. Restricting attention to Category 4–5 hurricanes (see below) shows no significant change. This overall decrease seems to be driven by more frequent La Niña years, which are associated with fewer hurricanes in the huge Pacific Ocean, and more in the smaller North Atlantic Ocean, giving a reduced total.

Global damage has increased significantly, however, due to having more people and more infrastructure in hurricane-prone coastal areas. It seems difficult to stop people from moving to Florida to live, so there is a clear need to make buildings and infrastructure more hurricane-proof. This document from the government of Queensland (Australia) offers some useful tips for home construction.

Figure 3c from Klotzbach et al. Category 4–5 hurricanes in six tropical cyclone basins during 1990–2021.

Italian Solar Challenge Results

Above are official lap counts (in two stints) for the recent Italian Solar Challenge at the Imola Circuit near Bologna.

Bochum reported electrical problems with their SunRiser, and did not race, although they had successfully completed a qualifying lap (both Bochum cars had driven all the way to Italy). The local Italian team had even more serious electrical problems.

According to the regulations, for the Challenger class, there should be added to the scores above:

  • 2 laps for the fastest lap during the race (Aachen gets this, with a time of 4:09.236 in the first stint, i.e. 70.9 km/h for the lap)
  • 4 laps for the pole position in the qualifications (Aachen gets this too)

Consequently, Aachen’s lap score should, I understand, be adjusted up to 95.

Update: it seems that the organisers have decided to retroactively merge the two classes. Rankings are therefore:

  1. Aachen
  2. Bochum
  3. Solaris
  4. Solis-EV

Italian Solar Challenge now on

The Italian Solar Challenge is now on at the Imola Circuit near Bologna. A calendar for the event is shown above. Further details and team social media links can be found on my annotated teams list. See also the race social media at    

The Covestro Sonnenwagen (left) and the thyssenkrupp SunRiser (right) are 2 of the 7 cars at the event (photos by Anthony Dekker, click images to zoom)


The start grid is shown below, courtest of team Sonnenwagen Aachen, who also have a livestream here. It seems that I was wrong in the pictures above; Aachen are racing only the three-wheel Covestro Photon. Bochum reports electrical problems with their SunRiser, which they expect to race only a few laps.

Explaining Doppler ultrasound

Recently, I posted something about fetal heartbeats. This seems to be a hot political topic at the moment in the US. Many people don’t seems to understand that, as I noted in my earlier post, the human fetus has a functional (though not yet fully developed) heart from about 21 days after conception.

There seems to be an even greater confusion about the physics of Doppler ultrasound machines. These do not “detect electrical signals,” as has been suggested, but are essentially “speed cameras” for blood (although they use sound rather than radio waves). They detect movement, because movement causes a change in sound frequency, through the Doppler effect. When the heart contracts and the blood is moving fastest, the velocity signal is greater. The pulsing of the resulting velocity signal matches the pulsing of the heart, and can be made audible, although the timbre of the resulting heartbeat sound will not be identical to what a microphone would detect.

The graphic below summarises the operation of the device, at three moments in time (A, B, C). The sound signal sent and received is shown in blue. At the bottom of the graphic is the velocity signal, with the three moments A, B, C marked.

Fetal development: what about marsupials and birds?

Recently, I posted something about fetal heartbeats. In humans (and in mammals generally), oxygen and nutrients are transferred by the mother’s circulatory system to the placenta, and from there by the separate fetal circulatory system to where they are needed. As I noted in my earlier post, this process is functional in humans at about 21 days after conception.

In order for this process to work, the fetus obviously needs a beating, functional heart (although the heart continues to develop after it starts beating). It also requires a different kind of hemoglobin, which binds more tightly to oxygen than the mother’s hemoglobin does, thus facilitating oxygen transport across the placenta in one direction. Waste products, including carbon dioxide, are transported across the placenta in the other direction. The water-filled lungs, obviously, play no role in absorbing oxygen or getting rid of carbon dioxide.

Human fetal circulatory system, showing the ductus venosus and ductus arteriosus which partially divert blood away from the liver and the water-filled lungs (from American Heart Association)

There are alternatives to this placental system, however. Marsupials, such as kangaroos, do not have the same kind of placenta. Kangaroos are therefore not able to survive in the womb longer than about a month. Instead, they are born in a partially developed state, and crawl to the pouch, where they complete their development drinking milk and breathing air with their still-developing lungs.

Young joey (baby kangaroo) in its mother’s pouch (photo by Geoff Shaw)

Birds have yet another approach, developing inside an egg. Nutrients are packaged inside the egg along with the embryo. Oxygen and carbon dioxide diffuse in and out through the eggshell, and oxygen is absorbed by the embryo through the allantois. The allantois also acts as a dumping ground for nitrogenous waste. When the nutrients in the egg are exhausted, it is time for the bird to hatch.

Chicken embryo on its 9th day (image by KDS4444)

Fetal heartbeat and political debate

Following the recent Dobbs v. Jackson Women’s Health Organization decision in the US, that nation is struggling with two moral/philosophical questions:

  • Is the unborn human fetus a person, and if so from when?
  • Does the unborn human fetus deserve legal protection, and if so from when?

These are independent questions – a puppy or kitten is not a person, but nevertheless has legal protection from animal cruelty. The now-repealed Roe v. Wade (1973) and Planned Parenthood v. Casey (1992) decisions essentially answered the second question as “yes, from viability.”

These questions are moral and philosophical, not scientific. However, scientific questions do arise in the debate. Is the fetus alive? Yes, obviously. Is it human? Well, it has different hemoglobin from adult humans, but the fetus is obviously Homo sapiens. Does the fetus have a heartbeat? Surprisingly, that seems to be controversial, although every textbook I have seen agrees that the heart is functional very early (how else would the developing fetus get oxygen and nutrients?). To quote some sources:

  • “The heart is the first organ to develop. In the human embryo, the heart begins beating at about 21 days after conception [i.e. 5 weeks after LMP = last menstrual period].” (Anatomy and Physiology of the Circulatory and Ventilatory Systems, page 2)
  • “The fetal–placental circulation begins at about 9 days postfertilization … A functional circulation is established by the end of the third developmental week [i.e. 5 weeks after LMP].” (Fetal MRI, page 405)
  • “In a developing embryo, the heart has developed enough by day 21 post-fertilization to begin beating [i.e. 5 weeks after LMP]. Circulation patterns are clearly established by the fourth week of embryonic life. It is critical to the survival of the developing human that the circulatory system forms early to supply the growing tissue with nutrients and gases, and to remove waste products.” (Anatomy and Physiology 2e)
  • “Circulation of fetal blood in the placental circulation begins approximately 21 days postfertilization in humans [i.e. 5 weeks after LMP].” (Handbook of Developmental Neurotoxicology, page 68)
  • “1. Fetal heart development begins during the first month of gestation. At about 21 days of gestation, the fetal heart begins beating, and blood begins circulating [i.e. 5 weeks after LMP]. Between the second and seventh weeks of gestation [i.e. 4 to 9 weeks after LMP], the primitive fetal heart undergoes a series of changes that create the four-chambered heart and its great arteries. 3. During gestation, the lungs are nonfunctional, and fetal oxygenation occurs via the placenta.” (Pediatric Nursing, page 223)

In my view, accurate discussion of the scientific facts is a necessary preliminary to addressing the moral and philosophical questions.

Doppler ultrasound is routinely used to detect fetal heartbeat and the velocity of fetal blood flow. The scientific principle known as the Doppler effect allows the detection of motion. It is the principle behind speed cameras, and it allows bats to “hear” the fluttering wings of a distant insect. During first-trimester screening (at around 11 to 13 weeks after LMP), professional Doppler ultrasound devices are sensitive enough not only to detect fetal heartbeat, but to detect blood flow abnormalities in various parts of the fetal circulatory system.

Fetal heartbeat at 13 weeks (from here). S is the ventricular systolic wave, D the early diastolic, A the atrial contraction.

European Solar Challenge: Further Analysis

I updated my previous post to include visualisations of the official results of the iLumen European Solar Challenge. However, a helpful commenter shared a link to the detailed lap data, so above and below is some further analysis on lap times. Colours are the same as in the previous charts. As always, click to zoom.

The chart at the top shows pit time (including recharging time) as almost-horizontal lines, and pit time is also visible as gaps in the chart below. The histograms show that Top Dutch (6), the two cars from Sonnenwagen Aachen (7 and 70), Istanbul Technical University (34), and the experienced drivers in BOSolarCar e.V. (11) were particularly good at driving consistent lap times.

Measured by median lap times, Stella Vita from Eindhoven (41), Covestro Photon from Aachen (7), SunRiser from Bochum (11), RED E from Twente (42), and BluePoint from Agoria (8) were the fastest cars.

European Solar Challenge Lap Data

All too soon, the 24-hour iLumen European Solar Challenge is over. The charts above and below (click to zoom) show results from the live timing board. The winners of the two classes (Challenger and CR = Cruiser) will be decided on points scores, which are still to come. Meanwhile, however, the German teams from Aachen and Bochum deserve special congratulations. For updates, see also the race social media at    

Update 1: there are apparently no official results yet. All that has been released has been the podiums:

  • Challenger: 1. Covestro Photon (Aachen), 2. Covestro Sonnenwagen (Aachen), 3. RED E (Twente)
  • Cruiser: 1. Lodz, 2. Onda Solare, 3. Stella Era (Eindhoven)

Using the guidelines in the official regulations, I can calculate the Challenger class scores (see below).

Update 2: the official results have now been released, and I have added the chart below. Bochum seems to have lost out from having a two-seater car. For the rest, practicality judging makes up 40% of the final Cruiser score at iESC, so that Lodz essentially won on practicality (although I note that four of the Cruisers raced in Australia in 2019, and I would have expected both practicality and efficiency scores at Zolder to have been somewhat similar).

Sasol Solar Challenge Results

The final day of the Sasol Solar Challenge saw the teams arrive in Cape Town, with Delft (Brunel) in the lead after 8 gruelling days. Brunel’s fantastic performance is tarnished somewhat by the fact that a member of one of the South African teams threw a tool (?!) at Agoria’s solar panel last night, seriously damaging it. Without that damage, it is possible that the Belgians could have won.

The updated chart above incorporates some minor corrections to previous days. Not shown in the chart is UniChamps (University of South Africa), the sole Cruiser class team.

See my annotated list of teams for all team social media links. The official race social media is at      

European Solar Challenge (iESC)

The iLumen European Solar Challenge in Belgium is about to begin – see my annotated list of iESC teams. The 24-hour track race will start at 13:00 on the 17th, continuing until 13:00 on the 18th. The image above shows Kratos EAFIT (from Colombia), Sonnenwagen Aachen (from Germany), Top Dutch (from the Netherlands), and Onda Solare (from Italy).

For fans at home interested in the weather, check the forecast. It looks like it will be rather wet, sadly. At the top of this page is a webcam nearby, looking west, towards the Zolder racetrack. This webcam is at the track itself (with a view of the “Kleine Chicane,” looking roughly north from just about the centre of the track). Circuit Zolder has a live timing board and tracker. See also the race social media at