1. Introduction

Chapter 1: Introduction

1.1 Engineering Problem

Currently, weather predictions are based on data collection points that the Meteorological Service placed around Singapore at 60 locations (NEA, 2013). As we are dependent on the data collection points placed island-wide, we are informed of the forecast only at the time when news is being broadcasted by the NEA website. Meteorological Service Singapore (MSS) has a Lightning Detection Network which comprises of only four lightning detection sensors located in the north, south, east and west sectors of Singapore. This network allows MSS to monitor the location of lightning. Having our own system for atmospheric observation will alert us about the weather faster and more accurately. 

Furthermore, forecasting is not based on SST, but rather on the 60 stations around Singapore. This makes the prediction inaccurate as weather is monitored and    predicted from weather stations not on site. With an On Site monitoring system, we are able to tell if there would be an impending storm and the predictions would most likely be almost 100% fool proof as we would have data that is collected from the environment around us on site. The information would also reach SST staff and students faster than other weather information providers and can easily be shared.

Having more than one type of sensor would help us identify the changes in the surroundings in terms of the different aspects (Humidity, temperature) so that we can use all the combined data to confirm it is indeed an approaching thunderstorm that is causing changes in the environment. Lightnings are usually associated with thunderstorms.(Weather Wiz Kids) This is to ensure our predictions are as accurate as possible as other factors or objects might affect only a certain aspect of the environment. Using the antennas that we have setup, we would be able to determine the disruptions in the magnetic field before the lightning actually hits, enabling us to predict when a thunderstorm would occur. The UFO Camera is just so that we can prove our findings and prove that it is a lightning and not other things that caused the disruption of the atmosphere before a thunderstorm. 

Also, current programmes for most of the system runs on Windows and not on Linux so it cannot be used in a Raspberry Pi. Our group will attempt to solve the compatibility issue such that the use of Windows can be minimised to save cost on licensing.

1.2 Engineering Goal

Our engineering goal is to develop an atmospheric observation system in School of Science and technology, Singapore. 

1.3 Specific Requirements

• A visual evidence of a bolt of lightning must be present. (Eyes)
• A graphical representation of a bolt of lightning must be present. (Ears)
• All systems must run 24 hours a day, 7 days a week.
• Setup at least 3 different systems for detection of lightning.
• Enable a cheap method of data collection.

1.4 Alternative Solutions

1.4.1 Lightning Electromagnetic Field

Thunderstorms are defined as “A transient storm of lightning and thunder, usually with rain and gusty winds, sometimes with hail or snow, produced by cumulonimbus clouds.”.

When heavy rain and strong winds are present, they create updrafts and downdrafts that are present simultaneously within close proximity with each other. The updraft caused by the winds and rain transports small water droplets to high heights that are way above freezing level. 

Meanwhile, downdrafts move the solid, already frozen water droplets down back to ground level.  

When the solid, already frozen water droplets collide with the liquid, small water droplets, both the water droplets turn into ice and gives out heat to the surroundings. This heat keeps the surface of the now solid water droplets warmer than the surroundings, thus forming graupel or soft hail. 

A phenomenon occurs when the soft hail or graupel collides with additional water droplets in solid or liquid forms. Electrons are transferred from water droplets that are going up due to updraft to ice particles that are going down due to downdraft. This creates a storm cloud with a negatively charged underside and a positively charged top. 

A moving thunderstorm usually gathers another bunch of positively charged particles beneath the thundercloud. The earth’s atmosphere is a great insulator that inhibits the flow of electricity from the cloud to the ground. Hence, a huge amount of electrical charge has to be built up in order for the phenomenon of a lightning to occur. This charges that are built up in the atmosphere then causes the distortions in the electromagnetic field when lightning strikes.

1.4.2 Lightning Visual 

The lightning visual will complement the lightning electromagnetic-field data to validate the occurrence of lightning. A UFO Camera (Watec 902H Ultimate Camera) will capture images and videos of the sky when there are sudden movements or flashes of light, usually caused  by lightning. 

Lightning is a bright flash of electricity produced by a thunderstorm. Lightning and thunder and both caused by electrical discharge in the atmosphere, but they are separated in order. Lightning is seen several seconds before thunder is heard, as light travels faster than sound. 

There are various types of lightning, all of which have different appearances and characteristics.

Cloud to ground lightning - It is the most dangerous type of lightning that comes from the negatively charged bottom of the cloud travelling to the positively charged ground. Cloud to ground lightning bolts often strike tall objects like trees and skyscrapers, starting fires and resulting in property damage and even death, if a human is the tallest object in a flat plain.

Figure 1.1: Cloud to Ground Lightning

Intracloud lightning - It is the most common type of lightning that occurs when there are positive and negative charges within the same cloud. Intracloud lightning usually takes place within the cloud and exhibits a diffuse brightening of the surface of a cloud. Intracloud lightning is also known as sheet lightning or anvil crawlers. 

Figure 1.2: Intracloud Lightning

Intercloud lightning - It is not common and it occurs when the strike travels in the air between different clouds with positive and negative charges.

Figure 1.3: Intercloud Lightning

Heat lightning - It is a lightning near on horizon that is reflected by high clouds that do not have accompanying sounds of thunder. This happens because the lightning occurs a very far distance away, and the sound dissipates before reaching the observer. The flashes of heat lightning usually have a faint appearance.

Figure 1.4: Heat Lightning

Bead lightning - It is a unique type of cloud to ground lightning that has a higher intensity of luminosity. It is known as the Bead lightning at it leaves behind a string of beads effect for a few seconds after the discharge fades. It is also known as chain lightning, as it lasts a longer duration than most typical lightning and appears segmented unlike the usual continuous channel. It happens infrequently but has been observed many times. The causes of Bead lightning are unknown, but some scientists believe that portions of the lightning channel are slanted away from the observer and thus seem brighter or dimmer. Another possible reason is that parts of the channel are blocked by rain or clouds.

Figure 1.5: Bread Lightning

Ball lightning - It is an atmospheric electrical phenomenon. It appears as a floating, illuminated ball that occurs during thunderstorms, making a hissing or crackling noise or no noise at all. Ball lightning lasts longer than common lightning flashes which last only a fraction of a second. It reportedly lasts for up to 20 seconds, but scientific data on Ball lightning is scarce as it rarely occurs and is extremely unpredictable. It has been known to pass through thick materials like glass windows, burn all objects in its path, and vanish with a loud explosion. The cause of Ball lightning is still unknown, but theories suggest microwave radiation, oxidising aerosols, nuclear energy, dark matter, antimatter and even black holes as possible causes. One of the most famous theories suggests that Ball lightning is burning silicon that has been vapourised by a lightning strike.

Ribbon lightning - It is a type of lightning that occurs during thunderstorms with high cross winds and multiple return stokes. The strong cross winds will blow the successive return strokes slightly to one side of the previous return stroke, causing a ribbon effect, thus the name Ribbon lightning.

Figure 1.6: Ribbon Lightning

Red Sprite - Sprites are large, luminous flashes that occur above active thunderstorm clouds and happen concurrently with cloud  to ground or intracloud lightning. They are electrical discharges that are triggered by the discharges of positive lightning between a thundercloud and the ground. Sprites are usually red and they come in a diverse range of visual shapes flickering in the night sky. Their spatial structures range from small single or multiple vertically elongated spots, to spots with faint extrusions above and below, to bright groupings which extend from the cloud tops to altitudes up to 95 km. The brightest region lies in the altitude range 65-75 km, where there is often a weak reddish glow or fine structure that extends to about 90 km above it. Blue tendril-like filamentary structures often extend downward below the red region, sometimes going as low as 40 km. Sprites often appear in clusters of two, three or more, sometimes extending across horizontal distances of 50 km or more. 

Figure 1.7: Red Sprite

Blue jet - Blue jets are a second high altitude optical phenomenon, distinct from sprites, observed above thunderstorms using low light television systems. As their name implies, blue jets are optical ejections from the top of the electrically active core regions of thunderstorms. Blue jets are not aligned with the local magnetic fields.

1.4.3 Solar Electromagnetic Field

A flare is defined as a sudden eruption of magnetic energy released on or near the surface of the sun and accompanied by bursts of electromagnetic radiation and particles. (“Solar flare,”) A solar flare occurs when immense amount of magnetic energy is released after building up for a long period of time. Radiation is emitted across the entire electromagnetic spectrum which includes light humans cannot see. These include radio waves, x-rays and gamma rays (Strickland). The first solar flare recorded was on September 1, 1859 by two scientists, Richard C. Carrington and Richard Hodgson, when they viewed a large flare in white light. (Kennewell)

As the magnetic energy is being released, particles, including electrons, protons, and heavy nuclei, are heated and accelerated in the solar atmosphere. (“Solar flare,”)

.

There are typically three stages to a solar flare. First is the precursor stage. This is when energy is released in the form of x-rays with lower wavelength. Soft x-ray emission is detected in this stage.

In the second or impulsive stage, ions, protons and electrons are accelerated nearly to the speed of light. During this stage, radio waves, hard x-rays, and gamma rays are emitted.

The last stage is called decay, and soft x-rays are the only emissions. The duration of each of these stages can last for seconds to hours. (O'Callaghan, 2012)

Solar flares extend out to the layer of the Sun called the corona. The corona is the outermost atmosphere of the Sun.

The frequency of flares coincides with the Sun's eleven year cycle. When the solar cycle is at a minimum, active regions are small and rare and few solar flares are detected. The number of active regions increase as the Sun approaches the maximum part of its cycle. (“Solar flare,”)  

A person cannot view a solar flare by simply staring at the Sun. Besides, looking directly at the Sun may cause irreversible permanent eye damage. Flares are hard to see against the bright emission of light energy from the photosphere. Special instruments are used to detect solar flares by detecting the radiation emitted by the flare. Radio signals and optical emissions from flares can be observed with telescopes on the Earth. As x-rays and gamma rays do not enter Earth’s atmosphere, telescopes in space are required to detect them. 

The SID (Sudden Ionosphere Disturbance) system consists of a square antenna and SuperSID program running on a Raspberry Pi. The square antenna present in the School of Science and Technology, Singapore is able to detect radio frequencies between the 0 kHz and 30 kHz range. Solar flares increases the ion density in the atmosphere and so does lightning. Monitoring VLF waves means monitoring the ion disturbances in the atmosphere. Thus, this system would also allow its user to detect lightning in the 0 kHz and 30 kHz range which might not be recorded by the VLF Radio system.

1.4.4 Weather Station

Another system capable of determining the presence of lightning would be the weather station. This system is called the Wireless Vantage Pro2. This weather station comes equipped with a rain collector, temperature sensor, humidity sensor, anemometer and a solar panel to power the sensors. Additional sensors such as UV sensors and soil moisture sensors can be added. The weather data can be transmitted wirelessly up to a range of 300 meters. The system also comes with a 9 cm x 15 xm LCD screen that can display the weather data.  There is an optional WeatherLink data logger and software that provides additional analytical capabilities. It is also possible to obtain weather data from the weather station from home as the system is also equipped with GSM interface. This can be accomplished by logging onto Vital Weather Portal. The portal provides detailed up to date weather information such as wind speed, temperature, air density and even cloud height and humidity. The portal is also able to record and store data. This system would be useful as information collected can be used to verify that a lightning strike did in fact occur. A decrease in temperature and increase in wind speed and rain fall might suggest that a thunderstorm took place. This information can then be used with graphs of other systems to verify that a lightning strike did happen as lightning are usually associated with thunderstorms. Information and data logged would not be erased as it would be stored on the internet. The problem of insufficient disk space to store data is also eliminated. As data logged come with a timestamp, it is possible to trace when the thunderstorm occurred and match it with data from other systems.

1.4.5 0-10 kHz VLF Radio System

This VLF Radio system consists of a vertical antenna, a VLF Radio capable of picking up frequencies between 0-10 kHz and computer software to log the data.

The VLF Radio, namely INSPIRE (or Interactive Nasa Space Physics Ionosphere Radio Experiments ) VLF-3 Radio Receiver is used to make observation of signals from sources in the ionosphere at audio frequencies. The VLF Radio was designed to be low cost and simple for students to assemble and operate. It was also designed to make use of a whip antenna. The VLF Radio filters out out-of-band signals that are undesirable and amplifies the desired signals until it is strong enough to be logged. The amplification process includes converting the

high impedance of the antenna to a lower impedance so as the enable efficient amplification.

The whip antenna forms an electric-field probe to pick up natural radio signals. The antenna is connected to the VLF Radio via a 10 meters coaxial cable with BNC (Bayonet Neill-Concelman).

The signal collected is then sent into the computer via a 3.5mm audio jack connected to the computer’s line in for the computer to process and log the data.

The output of the radio consist of two types, headphones/audio output and data output. The main difference is that signal coming out of headphones/audio output has gone through another layer of amplification.  The output at the data output jack does not have sufficient amplitude to drive a headphone and thus can only be logged but not listened to. The signal coming out of audio output has been amplified sufficiently to drive a set of headphones or small speakers. The audio output jack outputs audio in stereo but has the same signal applied to both the left channel and right channel. The final amplifier that amplifies the signal before it outputs from the audio output jack is not powered when the main power is on as it has its own power switch. This feature is to help save power.

The VLF Radio can be powered by an internal 9 VDC battery or external 9-14 VDC source. Diodes help to prevent external power source from charging the internal battery and vice versa.

The signal collected is then sent into the computer via a 3.5mm audio jack connected to the computer’s line in for the computer to process and log the data. The purpose of this system is to track lightning. In a storm cloud, the upper portion is positive and the lower portion is negative. How the clouds acquire this charge is still greatly debated amongst the scientific community. There is, however, a plausible explanation.

Part of the water cycle involves moisture accumulating in the atmosphere and coming together to form clouds. Rising moisture can collide with falling ice or sleet. Electrons are knocked off the rising moisture as the collision occurs and gathers at the lower portion of the clouds. This is what causes charge separation in clouds and thus form an electric field that is negative in the lower region and positive in the upper region. The electric field is so intense it repels electrons at the earth’s surface. This repulsion of electrons causes earth’s surface to have a strong positive charge. The electrons then travels through ionized air and towards earth. This is what we call lightning.

Radio waves can be generated by lightning, astronomical objects, communication satellites or radars. Most natural radio waves are generated by lightning. Each stroke of lightning emits a broadband pulse of radio waves at the same time a flash of visible light is emitted. ("Earth songs," 2001) The frequencies emitted by lightning strikes range from 0 Hz to over 100 kHz with all frequencies of radio signals emitted at the same time the visible flash of lightning is observed. ("Natural VLF radio," 2011)

The radio signal of each stroke of lightning, when received and amplified by the VLF radio, resembles the crackling sound of campfire. These emissions are called "sferics". When vertical lines are present on the graph, it indicates that all frequencies of radio signals are present. The design frequency range of the VLF-3 Radio Receiver is 0-10 kHz. ("Field equipment setup," ) Radio frequencies that are slightly above 10kHz can sometimes be detected. One of such examples would be the radio signals from Russia’s ALPHA navigation system which is used for long range radio navigation and transmits radio signals on the frequencies 11.905 kHz, 12.649kHz and 14.881kHz. (Trond) Even though they are higher frequency than the design of the receiver they are still sometimes detected because of their high signal strength. A quiet and typical condition would have about 20 strong sferics and a few weaker ones in a 10 second interval

Radio signals from lightning up to 3000 kilometers away can also be detected by the VLF-3 receiver as VLF radio waves emitted by lightning can reflect off a layer of charged particles (electrons) in the ionosphere redirecting the signal back toward the surface of the earth. The signal can then bounce off the surface of the earth, and again off the ionosphere. This process is repeated and thus radio signals can sometimes travel more than halfway around the earth. ("Natural VLF radio," 2011)

Radio signals of higher frequencies travel slightly faster than radio signals of lower frequencies and therefore get picked up by the VLF-3 receiver slightly ahead of the lower frequencies. This is called “dispersion”.("Dispersion,") The radio signals of lower frequencies gets picked up by the receiver only a few hundredths of a second slower and this leaves a characteristic imprint on a graph. The sound heard is an altered version of the dry crackling sound as described above.This is called a "tweek".

When the dispersion of frequencies in radio signals is more than 1 second and up to 3-4 seconds (Much greater than that of tweeks), it is an indication that the signal has traveled much further than half way around the earth. This is called a “whistler” ("Natural VLF radio," 2011)

1.5 Final Solutions

• Lightning Electromagnetic Field
• Lightning Visual
• Solar Electromagnetic Field

We chose three solutions to have many different sources of data as possible. These three final solutions combined together, will allow us to confirm that the fluctuations of the graphs are caused by the occurrence of thunderstorms. We will also be able to predict impending thunderstorms by observing disruptions in the atmosphere. We chose these three solutions because our group would like to have a system that will allow us to make accurate predictions about the weather in the School of Science and Technology, Singapore.  This system has the potential to inform the entire school population about weather changes around school as soon as possible, so that they have time to make alternative arrangements for the day’s event. Furthermore, these three solutions are cost efficient and require easily-accessible materials.