Encyclopaedia: Geospace

A contribution which I wrote for Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions. As a side note, I am normally quite pedantic about "Earth" and "Sun" being capitalised but the editor of the Encyclopaedia evidently had different views on this point.

The space immediately around the earth, including the upper atmosphere, ionosphere, and magnetosphere, is known as geospace. This region is of considerable scientific interest since it is the environment inhabited by most artificial (communication, navigation, meteorological, etc.) satellites. In addition to in situ measurements, observations of geospace are commonly made at high latitudes because the earth’s magnetic field focuses phenomena from a large volume of space down onto a relatively small portion of the earth’s surface. Both the Arctic and Antarctic are suitable sites. However, the Antarctic continent provides a better environment for the construction of research facilities. A significant number of countries with bases in Antarctica are engaged in geospace research.

Geospace is filled with plasma, which is a partially or fully ionized gas. As the fourth state of matter, plasma has characteristics that are completely different from those of neutral gas: the motions of charged particles in plasma are strongly influenced by externally imposed magnetic fields, as well as the electric fields from other charged particles and electromagnetic waves. This has important consequences for charged particle dynamics as well as the propagation of electromagnetic waves.

The plasma in geospace is permeated by the earth’s magnetic field and largely controlled by it. The earth’s intrinsic magnetic field is roughly dipolar (similar to that of a bar magnet). Magnetic field lines radiate outward from the surface of the earth near the North Magnetic Pole and extend a great distance into space before converging near the South Magnetic Pole. The magnetic field lines therefore cluster near the poles but are widely separated in the equatorial plane. For example, field lines separated in latitude by 60 miles (100 km) near the magnetic latitude of 60° on the surface of the earth are separated by about 900 miles (1500 km) in the equatorial plane. This means that a relatively small area on the earth’s surface maps to a very large volume of geospace. The magnetic field lines near the magnetic poles therefore act like an enormous funnel, concentrating the influences of most of geospace down onto only a small portion of the surface of the planet. Somewhat surprisingly, the earth’s North Magnetic Pole is currently located in the Southern Hemisphere (64° S 138° E), which is off the coast of Antarctica. The South Magnetic Pole is in the Canadian Arctic territory.

The geospace environment is linked to the sun by the interplanetary magnetic field (IMF) and the solar wind. The solar wind is plasma that flows at supersonic speeds (typically around 400 km/s) from the surface of the sun. The solar wind exerts pressure on the earth’s magnetic field, confining it to a cavity known as the magnetosphere. The orientation of the IMF and the speed and density of the solar wind, which vary with solar activity, have a marked effect on the state of the magnetosphere. The magnetosphere forms an enormous plasma physics laboratory, orders of magnitude larger than any terrestrial laboratory. This means that large-scale plasma physics phenomena, which are impossible to replicate on earth, can be studied.

Charged particles move easily parallel to magnetic field lines. However, the Lorentz force causes them to gyrate in a plane perpendicular to magnetic field lines. As a result, ions and electrons in the magnetosphere move on spiral paths along magnetic field lines. As a charged particle approaches a magnetic pole, the magnetic field strength increases and the speed of the particle along the magnetic field line is reduced. At some point, the particle is reflected back up the magnetic field line into the magnetosphere. This mirror point is at an altitude determined by the particle’s velocity. If the mirror point is within the neutral atmosphere, then there is a high probability that the particle will collide with a neutral atom or molecule, in which case it will lose energy and will not return to the magnetosphere. Such a particle is said to have precipitated. Positive and negative charged particles also drift in opposite directions around the earth, forming a ring current that causes measurable magnetic effects on the earth’s surface.

The aurora australis and aurora borealis (the southern and northern lights) are caused by energetic electron precipitation. Collisions between these electrons and neutral atoms or molecules in the upper atmosphere leave the neutrals in an excited state from which they subsequently decay by emitting light. Typically, the light is either green, red or violet, depending on the altitude of the emission. Green aurora, the most common, is due to the excitation of atomic oxygen.

Cosmic rays are extremely high-energy particles originating from outer space, generally outside the solar system. Most cosmic rays are atomic nuclei (predominantly hydrogen and helium atoms stripped of their electrons). They produce a cascade of secondary particles when they enter the earth’s atmosphere. Some of these secondaries are able to penetrate the earth’s surface. Since cosmic rays are charged particles, they too are able to access the earth’s lower atmosphere more readily near the magnetic poles. Only the most energetic cosmic rays can penetrate to the ground near the equator.

Certain electromagnetic waves are also affected by the earth’s magnetic field. Whistler-mode waves propagate along magnetic field lines through a plasma. Lightning strokes are the main source of whistler-mode waves. Some electromagnetic energy from lightning penetrates through the ionosphere and enters the magnetosphere, where it propagates in the whistler mode. Magnetic field lines guide the waves to the opposite hemisphere where they penetrate down through the ionosphere to reach the ground. The whistler mode is dispersive, which means that distinct frequencies travel at different speeds. The brief electromagnetic pulse generated by lightning is thus transformed as it passes through the magnetosphere into a unique signal that emerges in the opposite hemisphere. This is called a “whistler.” Measurements of whistler dispersion are used to determine plasma densities at great distances from the earth, which otherwise could be measured only by satellites.

Encyclopaedia: Scottish National Antarctic Expedition

A contribution which my wife and I wrote for Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions.

The Scottish National Antarctic Expedition explored and performed scientific work in Antarctica between 1902 and 1904. This expedition was novel because it was organized and led by a natural scientist, and science was thus a priority. William Bruce (1867–1921) was a former medical student with an interest in the natural sciences, particularly oceanography. He had his first taste of the Antarctic on a whaling voyage in 1892 and subsequently went on several trips to the Arctic. Bruce had applied to join the Discovery Expedition and, after receiving no response, proposed a second ship for this expedition. This proposal was rejected. As a result, he set about obtaining private funding for an independent Scottish expedition.

Bruce secured a substantial donation from the Coats family, with which he purchased a Norwegian whaling vessel. This ship was extensively modified, with the addition of scientific laboratories and diverse experimental equipment. Its hull was reinforced, and auxiliary engines were added. Upon completion, she was renamed Scotia. The expedition scientists consisted of an oceanographer, zoologist, botanist, taxidermist, geologist, and physicist. These positions, as well as the captain, officers, and crew of the Scotia, were all filled by Scotsmen.

Scotia departed from Scotland on November 2, 1902, reaching the Falkland Islands on January 6, 1903. There she took on provisions and soon afterward left for the Southern Ocean. The first stop was at the South Orkney Islands, where botanical and geological samples were taken. Toward the end of February 1903, the Scotia had reached 70° S, but as the sea began to freeze over, she was forced to retreat northward, returning to overwinter at Laurie Island in the South Orkneys. During the winter, the scientific program commenced in earnest. A stone building, Ormond House, was constructed on the island, to serve as accommodation for the meteorological station that was to be established there.

Toward the end of November 1903, the ice holding the Scotia broke up, and she departed again for the Falkland Islands and hence to Buenos Aires for provisions and repairs. A small party was left at Ormond House. Bruce persuaded the Argentinean government to support the observations being made on Laurie Island, handing Ormond House over to them. The building was renamed Orcadas Base. The Scotia returned to Laurie Island before once again sailing south to the Weddell Sea. After proceeding unimpeded for some time, she encountered heavy pack ice and shortly afterward the ice shelf. Sailing along the ice shelf they sighted land, which Bruce named Coats Land. The Scotia got to 74° S before gathering ice forced her to again turn northward. She then proceeded to Cape Town via Gough Island, where scientific specimens were collected. From Cape Town she sailed home, arriving on July 21, 1904.

Orcadas Base on Laurie Island. Image courtesy of http://www.culturademontania.com.ar/.

Orcadas Base on Laurie Island. Image courtesy of http://www.culturademontania.com.ar/.

Upon their return, Bruce and the captain of the Scotia were presented with medals from the Royal Scottish Geographical Society. However, unlike the members of the Discovery Expedition, none of the expedition members received Polar Medals. The expedition left a substantial scientific legacy. It returned with an extensive catalog of animal species, many of them previously unknown. The Scottish Oceanographical Laboratory was established by Bruce in Edinburgh to house these specimens. The Orcadas Base on Laurie Island is the oldest Antarctic base still in operation.

Font Awesome in Presentations: Notes

I've used various icons from Font Awesome in my last few presentations and I've been very pleased with the results. Using them is pretty straight forward, but here are a couple of things that I picked up:

  • copy the icons straight from the Cheat Sheet;
  • if you are unable to paste the icon (or you just get a little square instead of the eye candy you were expecting), try selecting the "Keep source formatting" option when you paste.

Encyclopaedia: SANAE IV

A contribution which I wrote for Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions.

sanae-iv-A

South Africa is one of the founding signatories of the Antarctic Treaty of 1959. In 1960, the first South African National Antarctic Expedition (SANAE) team overwintered at the Norwegian base on the Fimbul Ice Shelf. A new base, SANAE I, was constructed nearby (70° 18′S 2° 22′W) and opened in 1962. Later bases, SANAE II and SANAE III, were built on the same location (72° 40′ 22″S 2° 50′ 26″W) and commissioned in 1971 and 1979 respectively. SANAE I and II were simple wooden structures with a limited life span. SANAE III was more robust, housed in horizontal corrugated steel cylinders. However, as SANAE III disappeared beneath the accumulating snow, it was subjected to crushing pressure and ultimately abandoned in 1994. The current South African research station, SANAE IV (72° 40′ 22″S 2° 50′ 26″W), is located in the Norwegian territorial claim of Queen Maud Land, some 90 miles (150 km) from the edge of the ice shelf. In contrast to earlier bases, which were built on the ice shelf, SANAE IV is perched at an altitude of 2,800 ft. (850 m) above sea level on top of the sloping plateau of Vesleskarvet, an isolated nunatak on the edge of the Ahlmann mountain range.

SANAE IV was completed in 1997 with a designed life span of about 25 years. It was built to withstand temperatures as low as −67°F (−55°C) and wind speeds up to 155 mph (250 km/h). Most of SANAE IV was prefabricated in South Africa. The structure consists of a steel framework cladded with thick foam and fiberglass composite panels. The base is about 575 ft. (175 m) long with three linked modules, each of which is 144 ft. (44 m) long, 46 ft. (14 m) wide, and has two interior levels. The southern module, A-block, contains accommodation, ablution facilities, a laundry, radio room, hospital, and various offices, laboratories, and storerooms. B-block houses further accommodation and ablution facilities, another laundry, the kitchen and dining area, cold and dry stores, library, and entertainment areas. Finally, C-block contains the diesel generators, water storage and sewage processing plant, storerooms, engineering offices, gymnasium, sauna, and a helicopter hangar.

SANAE IV is elevated 13 ft. (4 m) above the surface on steel stilts, securely anchored into exposed rock. The elevated structure accelerates snow blowing through beneath the base. Since SANAE IV is located near the edge of a cliff, which is downwind of the prevailing wind direction, most of the snow that might have accumulated in the lee of the base has been blown over the cliff.

The base is powered by three 250 kW diesel generators. The internal temperature of the living areas is maintained using heat from the generators’ exhausts. Potable water is produced by a snow smelter located a small distance from the base and which must be regularly filled with fresh snow. SANAE IV has a sophisticated communications infrastructure based on HF radio and satellite systems. The satellite connection provides telephone, fax, and Internet links. The operation of SANAE IV emphasizes environmental responsibility, and every effort is made to prevent contamination of the local environment. All waste material is sorted and then returned to South Africa for disposal or recycling.

SANAE IV can accommodate around 80 people during the summer relief period and up to 18 overwintering team members. The overwintering team typically consists of two or three scientists, a meteorologist, two diesel mechanics, electronic, electrical and mechanical engineers, and a doctor.

sanae-iv-B

It is possible to fly from Cape Town to a blue ice runway near SANAE IV, but the costs are prohibitively high. Personnel, supplies, and equipment normally reach SANAE IV by sea. The annual relief voyage departs from Cape Town around the beginning of December every year and returns toward the end of February the following year. The SA Agulhas, the ship that has serviced SANAE bases since 1978, was replaced by the new SA Agulhas II in 2012. Once the supply ship reaches the ice shelf, personnel and sensitive equipment are airlifted to the base by helicopter, while the remaining cargo is transported over land by caterpillar train.

The base hosts a number of high-profile science projects. During the summer months, research is conducted in biology, renewable energy, geology, and geomorphology. Research in the physical sciences extends throughout the year, and a range of sophisticated experiments operate continuously in the vicinity of the base, such as the following: (1) the motion of ionospheric irregularities is measured by the Southern Hemisphere Auroral Radar Experiment (SHARE), a 16-element high-frequency coherent radar array. The radar can also detect the trails of ionization from meteors. The SHARE radar forms part of the Super Dual Auroral Radar Network, operating in conjunction with other radars on the continent. The field of view of the SHARE radar overlaps with those from the radars at Halley and Showa stations. The direction and velocity of ionospheric convection can be determined where the fields of view from two or more radars overlap; (2) properties of the magnetosphere are deduced from very-low-frequency (VLF) radio wave measurements made using a pair of orthogonal loop antennas. VLF waves originate from lightning activity and natural processes in the magnetosphere. The VLF system also contributes data to the World Wide Lightning Location Network; (3) the proportion of electromagnetic waves that are absorbed by the ionosphere is measured by a 64-beam imaging riometer, which monitors the radio noise originating from deep space; (4) the earth’s absolute magnetic field strength, as well as fluctuations in the field, are measured using magnetometers; (5) a dual-frequency GPS receiver measures the total electron content of the ionosphere; (6) a scintillation monitor detects rapid fluctuations in GPS signals that are caused by small-scale irregularities in ionospheric density; (7) the flux of galactic and solar cosmic rays are studied using neutron monitors; and (8) a satellite telemetry station, which was installed for the Astrid 2 Swedish microsatellite, provides data downlink facilities. (9) A complete range of meteorological instruments supply weather data.

First Steps with Tableau: Decimal Separator

I downloaded a trial version of Tableau today and tried it out on one of the data sets I am currently working with. The data are stored in XLSX. Both the spreadsheet and my locale have a period set as the decimal separator, yet when I imported the data into Tableau it used a comma as the decimal separator.

This confused me.

Fortunately there is an easy fix. From the Worksheet view, select File then Workbook Locale. Neither the Automatic not the English (South Africa) gave me the correct results. But selecting English (United Kingdom) sorted the problem.

tableau-menu-locale

Dealing with a Byte Order Mark (BOM)

I have just been trying to import some data into R. The data were exported from a SQL Server client in tab-separated value (TSV) format. However, reading the data into R the "usual" way produced unexpected results:

> data <- read.delim("sample-query.tsv", header = FALSE, stringsAsFactors = FALSE)
> head(data)
                                   V1    V2
1 7E51B3EC4263438B22811BE78391A823  2129
2    8617E5E557903C7FAF011FBE2DFCED1D  3518
3    1E8B37DFB143BEEEE052516D2F3B58F5  6018
4    60B8AA536CFD26C5B5CF5BA6D7B7893C  7811
5    5A3BA8589DCD62B31948DC2715CA3ED9 12850
6    3552BF8AF58A58C794A43D4AA21F4FBA 13284

Those weird characters in the first record... where did they come from? They don't show up in a text editor, so they're not easy to edit out.

Googling ensued and revealed that those weird characters were in fact the byte order mark (BOM), special characters which indicate the endianness of the file. This was quickly confirmed using CYGWIN. (Yes, shamefully, I am working under Windows at the moment!)

cygwin-bom

The solution is remarkably simple: just specify the correct character encoding.

> data <- read.delim("sample-query.tsv", header = FALSE, stringsAsFactors = FALSE, fileEncoding = "UTF-8-BOM")
> head(data)
                                V1    V2
1 7E51B3EC4263438B22811BE78391A823  2129
2 8617E5E557903C7FAF011FBE2DFCED1D  3518
3 1E8B37DFB143BEEEE052516D2F3B58F5  6018
4 60B8AA536CFD26C5B5CF5BA6D7B7893C  7811
5 5A3BA8589DCD62B31948DC2715CA3ED9 12850
6 3552BF8AF58A58C794A43D4AA21F4FBA 13284

Problem solved.

Book Review: Graph Databases

The book Graph Databases by Ian Robinson, Jim Webber and Emil Eifrem gives an engaging overview of Graph Databases, describing typical use cases and illustrating the syntax used to construct and query them.

graph-databases-cover

Graph Databases are a form of NoSQL database and, as such, differ significantly from the ubiquitous Relational Databases. The authors discuss a variety of scenarios where a Graph Database would be a better fit than a Relational Database, showing how they are particularly well suited to data which describe relationships between entities.

Although there are a number of Graph Database implementations available, the focus of this book is on Neo4j. However, the treatment of the topic is still sufficiently general that you're not tied into this particular technology.

A chapter is devoted to the topic of Data Modeling with Graphs, where the CYPHER query language is introduced. A number of examples illustrate the basic syntax. Common graph modeling pitfalls (and ways to avoid them) are discussed. Other topics covered are building an application based on a Graph Database, graphs in the Real World, the internals of a Graph Database and Predictive Analytics.

After reading this book I have a solid understanding of where I will be using a Graph Database. I also have a feeling for how to structure my models and what my CYPHER queries will look like. If you need a general introduction to Graph Databases, then this book is a worthwhile read.

Book Review: R for Business Analytics

The book R for Business Analytics by Ajay Ohri sets out to look at "some of the most common tasks performed by business analysts and helps the user navigate the wealth of information in R and its 4000 packages." In my opinion it succeeds in covering an extensive range of topics but fails to provide anything of substantial use to its intended audience. At least, not anything that could not be uncovered by a brief internet search.

R-for-Business-Analytics

There is little detailed treatment of any particular topic related to Business Analytics. It is, at best, a high level overview of many of the capabilities of R. There is scant logical flow and the book appears to have been cobbled together from information readily available on the Internet. The editing is questionable and the code examples are poorly formatted. I also found the use of eponymous variable names in many of the code examples a little disturbing: is this really good practice? I don't think so.

Admittedly the author points out that the book is not aimed at statisticians, but rather at analytics professionals and students, where previous experience with R is not a prerequisite. However I suspect that neither of these groups would find the book very fulfilling.

Not everything about the book is bad though: the author does cover a diverse range of packages and I was pleased to learn about some interesting packages, of which I was previously unaware.

I feel a little uncomfortable posting such a negative review. For a more positive take on the book, you can read this review. However, if you are considering buying this book, I would personally advise against it. I felt more than a little cheated.