Justice - summary of findings - part three: rain, lightning and cyclones

Lightning was first observed on Jupiter when Galileo's capsule penetrated the atmosphere, although less frequently than on Earth. The scope of lightning is one tenth of those that occur in our world, but their intensity is tens of times higher

rain

On Jupiter there are two types of rain. One rain is related to the clouds and another rain is related to its nucleus. Rain of the first type - on Earth the rain reaches the ground, is absorbed by the soil and enters back into the familiar water cycle. On Jupiter, the rain evaporates on its way down, is immediately returned to the system, rises and evaporates, falls back, evaporates and returns, God forbid (26). The second type of rain is associated with helium deep inside Jupiter. The findings of the Voyagers support the previously controversial hypothesis that deep inside the planet there is a shower of helium. At very great depths, the atmospheric pressure is millions of times greater than that on Earth, to the extent that helium behaves like a liquid. It does not mix with hydrogen. Because helium is heavier, it gradually sinks toward the center of Jupiter (12).

lightning

Lightning was first observed on Jupiter when Galileo's capsule penetrated the atmosphere, although less frequently than on Earth. The extent of lightning is one tenth of those that occur in our world, but their intensity is tens of times higher (11).

The Galileo spacecraft itself discovered on the night side of Jupiter that lightning is controlled by large-scale atmospheric circulations associated with low-pressure areas (27). Galileo's findings show that lightning occurs mainly in belts and is associated with clusters of high, bright, thick clouds that appear suddenly and grow within a few days to dimensions of 1000 km. At the tops of the cloud clusters the atmospheric pressure is hundreds of millibars, a place where water, ammonia and H2S probably condense (14). The lightning was observed in a limited number of latitudes. Areas of anti-cyclonic shear. The depth of the atmospheric penetration of the lightning can be learned from the size of the light spots in the clouds. The larger the stain, the deeper the electrical breakdown. According to Galileo's findings, lightning appears in layers where water clouds are expected to form (12).

The New Horizons spacecraft detected nightside lightning at high latitudes, showing that convection currents are not limited to low latitudes. The meaning is an internal heat source. Their intensity is consistent with previous lightning measurements at low latitudes, equivalent to strong illuminations of terrestrial superbolts (28).

haze
Jupiter has a haze layer that is high above the main cloud layer. This finding was not surprising in view of the fact that for a long time it was known that there is a large amount of methane in its atmosphere. The methane at high altitudes is subject to the influence of the ultraviolet radiation coming from the sun and that it breaks down and forms more complex hydrocarbons that condense into droplets.

A preliminary analysis of the Galileo findings raised the possibility that Jupiter's haze is made of two layers, one high in the stratosphere associated with tholin (ie muddy) derived from methane, and the second layer in the upper troposphere (21). Haze also covers the Great Red Spot (29). Observations made on 16/17-8/2008 using ESO's very large telescope testified to large changes in the brightness of the equatorial haze found in belts 16,000 km wide at the equator. A large reflection of the haze in the upper atmosphere means that the haze has grown or that it has risen to a greater height. The bright part moves south more than 6000 km. These findings were reached following a comparison with observations by the Hubble telescope in 2005. The Hubble observations made at wavelengths in the near-infrared wavelengths used by the VLT (very large telescope) showed more haze in the northern half of the bright equatorial zone, while the VLT observations in 2008 showed a movement towards South (30).

Spirits

The speed and direction of the winds on Jupiter are determined by measuring the changing position of the clouds in the atmosphere. In January 1998 the Galileo capsule measured winds at a speed of 530 km/h and after a few months it increased to 640 km/h. The identification of the constant winds under the cloud that was discovered, raised the possibility that the heat escaping from the depths of the planet drives them and not the heat of the sun 11).

The bands of Jupiter have different dimensions, each band has its own width and the wind speeds are different. These remained constant during the telescopic observations and the Galileo observations. In several photographs the wind could be seen because it was pulling the clouds. The maximum speed measured in this observation was 460 km/h (31).

A comparison of the measurements made by the Voyager spacecraft in 1979 and Cassini showed that the wind system has hardly changed. The direction of the winds corresponds to that of the clouds. They blow towards the east on the side facing the equator of the dark belts and west on the side facing the poles. The strongest winds are at the equator and their speed reaches 612 km/h when they are in the east direction. There are two types of winds: strong, broad winds clustered around the equator and winds at higher latitudes. The latter are weaker and narrower. A group of researchers from Germany, Canada and the USA presented a computer model that takes into account all the characteristics of the wind system on the planet and according to which the winds reach a depth of 7000 km in the atmosphere. Two possibilities have been put forward to explain the behavior of the spirits. The shallow option and the deep option (in terms of depth of penetration into the atmosphere). Those in favor of the shallow approach applied techniques developed for terrestrial meteorology.

Because the Earth's atmosphere is very thin (compared to its size), it can be treated as a simple layer, allowing the computer simulations to move faster. The models were able to produce a number of banded winds, but they failed because Jupiter's equatorial winds move stronger and in the opposite direction and for this reason the distinction between the shallow and deep options falls away. All spirits are equal. In 1970 the first deep approach was developed. An important difference between the atmospheres of Earth and Jupiter is that Earth's atmosphere is bounded by its solid ground, while Jupiter is a gaseous planet. There is no bottom that confines the spirits to a thin layer.

As you go deeper into the atmosphere, the hydrogen molecules are compressed until they behave like a metallic substance and in terms of electrical conductivity. Jupiter's strong magnetic field prevents rapid movement in the deep areas that conduct electricity through a mechanism that acts as an eddy current brake. This mechanism dampens the fast currents to the outer 10% of the star's radius. Based on this approach, a model of the outer layer was built that refers to the outer 7000 km of the atmosphere (32).

Based on the Cassini measurements from 2000, a speed map was built showing speeds in the range between S°70 - N°70. The average speed reaches 400 km/h (20). In this context it is worth noting that the Galileo capsule measured the wind speed up to a depth of 70 km, and below that the speed is stable up to a depth of 150 km. The high speed at this depth is not the result of cloud convection and actually reflects the internal circulation of the planet. With the acceleration of the horizontal velocities, the upward flow is not simply vertical, but strongly driven by the winds and relative to the cloud tops are almost horizontal (33).

storms

The storms on Jupiter are enormous in size, 2 times larger than earthly storms that are accompanied by fast winds that can last for days and lightning, although the origin of the storms on Earth and Jupiter is different in both cases, they are characterized by a similar process: air rising which leads to rain (26). Thousands of spots were observed, each of which is a storm equal in size to the largest earthly storms: many of them change location, move to different latitudes or merge with others, and among these were found some whose lifespan was 70 days (7).

Cassini observed what appeared to be small, white storms that were engulfed by other systems around the Great Red Spot, breaking up and entering shear zones created by pressure differences. This spacecraft also discovered long-lasting storms at the poles as well (34). Eddy storms observed in 2006 and monitored by the Hubble telescope and the Keck Observatory were also observed in 2008. The storms around the Great Red Spot, in one year, turned from quiet to powerful eddies on both sides of the spot (19).

An observation made by the Hubble telescope as a backup to the observation made by the New Horizon spacecraft observed a storm that within 24 hours grew from a diameter of 400 km to a diameter of 2000 km. According to estimates, light storms form between the deepest water clouds, rise with great force and inject a mixture of ammonia ice and water up to a height of 30 km above the visible clouds. They move at a maximum speed of 600 km/h and create swirls of red clouds that surround the entire planet. A comparison between observations made in 1975 and observations made in 1990 indicates a similarity. 3 observed storms have a cycle time of 15-17 years. The storms erupt at the peak of the wind in terms of speed and two storms moving at the same speed were always seen (35).

An interesting observed phenomenon is the merging of 3 large storms, each the size of half the Earth, which lasted for 60 years. The process began in 1939-1940 when they noticed 3 storms that were given the name white ovals that were created in these years. The end product is a 12,000 km storm. The merging process began with the merging of two storms in 1998 and ended with the merging with a third storm that ended in 2000. Each of them was a high-pressure vortex rotating around itself with winds moving counterclockwise at a speed of 470 km/h (36). The combined storm's location is at W°350S°33 and it is rotating counterclockwise (37).

Cyclones

As on Earth, so also on Jupiter the air moves counterclockwise around low pressure areas in the Northern Hemisphere and clockwise around low pressure areas in the Southern Hemisphere. The low pressure areas are called cyclones and the high pressure areas are called anticyclones. On Jupiter, the cyclones have an amorphous and eddy structure that spreads out from their center in an east-west direction. The Vigers discovered that they were spewing out bright, expanding clouds that looked like large balls of lightning. Galileo confirmed the assumption that convection currents operate in these areas. In one case, one of these bright clouds was absorbed on the day side of Jupiter and two hours later it shone on the night side. The anticyclones are elliptical in shape, stable and long-lived like the Great Red Spot. No lightning was seen in the anticyclones. The likelihood is that the anticyclones do not attract energy below the convention currents. They act differently from Jupiter's hurricanes. They sustain themselves by merging with smaller structures ejected from cyclones, a phenomenon observed by the Vigers and Galileo (27).

Convection currents

Two cloud regions of Jupiter are distinguished. The zones where there are relatively many clouds and the belts are less cloudy. This is because energy coming from the planet moves towards the tops of the ammonia clouds where it is projected into space. This process creates planetary-scale convention cells with radial symmetry due to the planet's rapid rotation around itself. The upward moving part of each convention cell contains condensates such as water and ammonia that condense at the appropriate temperature and pressure for each of them, forming the ZONES clouds. The downward moving part of each cell is relatively emptied of volatiles, less cloudy and therefore creates the belts.

A third hot spot area must be added to these two areas. In these areas the local meteorological conditions are completely free of clouds, at least up to the level where the water condenses and even in lower areas. The discovery of a deep water cloud by the Galileo spacecraft upon penetration of the capsule into the atmosphere inside the hot spot where it found no water at all led to the conclusion that the deeper clouds have no horizontal homogeneity. This conclusion was not surprising because the convention cells in Jupiter must reach great depths not necessarily as individual cells. Chains of cells may be more stable (21).

Even before the spacecraft were launched towards Jupiter it was known that it emits twice as much heat as it absorbs from the sun. Upon the arrival of the spacecraft it became clear that this process is related to the currents of the convention. Since the sun's energy on Jupiter is only 2% of that reaching the Earth, it was clear that the source must be internal, and that it is responsible for the various storms on its surface. Also the colored strips of clouds in the east-west direction, whose speed reaches 4 km/h, are driven by the convention currents (480).

Hot spots

There are two types of hot spots in the atmosphere. One type is the set of dark areas found in the belts. These appear very bright in thermal emission especially in the near 5 micron wavelength range. The gaseous components are hydrogen, helium, methane and ammonia. It seems that these areas are relatively free of clouds, a place where emission occurs from depths of 8 atmospheres and the temperature close to 27°C reaches space. High-resolution spectroscopy can sense temperatures high enough that water vapor and phosphine (PH3) can be present (21).

A second type exists in the North Pole. These are hot pulses emitting X-rays that were discovered by the Chandra X-ray satellite. It was estimated that the source of the X-rays must be distant from Jupiter itself. The observation in which this phenomenon was discovered was on 18.12.2000 when the Cassini spacecraft passed by Jupiter. It turned out that most of the X-ray pulses come to the hot spot from a fixed source near Jupiter's north magnetic pole. In this place, energetic infrared and ultraviolet emissions were also discovered. The X-rays emit pulses in 45-minute cycles, similar to the high-latitude emissions detected by the Galileo and Cassini spacecraft.

An X-ray glow has long been detected by satellites near the poles. The researchers could not determine the exact location of this radiation. It was believed that the X-rays were created by energetic oxygen and sulfur ions. These ions originating from the moon Io are stimulated as they move around Jupiter within its magnetosphere and some are ejected into the atmosphere on their way back to Io's orbit. The Chandra satellite showed that this approach is wrong. These ions cannot reach the high latitudes where most X-rays are observed. Due to the large distances, about 30 radii of Jupiter, there are not enough energetic ions that can match the observations in which the X-ray emission was distinguished.

One possibility that has been put forward to solve the problem is that heavy ions emitted from the Sun as the solar wind are trapped in the outer regions of Jupiter's magnetic field and are accelerated and directed towards the planet's magnetic pole. At this time they move back and forth within the magnetic field itself from pole to pole. The oscillating motion can explain the X-ray emission (38).

26. Britt RR – “Stormy weather: Juvian superstorms like those on Earth” 9.2.2000
http://www.space.com/scienceastronomy/solarsystem/jupiter-weather-000209.html
27. Tindal R. – "Galileo data show Jupiter's lightning associated with low pressure regions" 13.10.1998
http://www.caltech.edu/~media/Press_Releases/PR11933.html
28. PIA10096: Polar lightning on Jupiter
http://photojournal.jpl.nasa.gov/catalog/PIA10096
29. Britt RR – “Mysteries dark spot near Jupiter's pole” 13.3.2002
http://www.space.com/scienceastronomy/solarsystem/jupiter-spots-020313.html
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http://www.spaceflightnow.com/news/n0810/02jupiter
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http://www.spacedaily.com/news/jupiter-clouds-05d.html
33. Seiff A. "Dynamics of Jupiter's atmosphere" Nature vol. 403 10.2.2000 pp. 603-605
34. "Nasa images show persistent Juvian polar storms" 16.7.2001
Http://dailynews.yahoo.com/h/nm/20010716/sc/Space_Jupiter_dc_3.html
35. "The mystery of Jupiter's jets uncovered" 25.1.2008
Http://www.spacedaily.com/reports/The_Mystery_Of_Jupiter_Jets_ Uncovered_999.html
36. Bridges A. "Jovian storms collide and merge" 24.10.2000
http://www.space.com/scienceastronomy/jupiter-spots-001024.html
37. PIA01651: Dynamics after historic mergers of storms on Jupiter”
http://photojournal.jpl.nasa.gov/catalog/PIA01651
38. "Jupiter hot spots makes trouble for theory" 28.2.2002
http://www.spaceflightnow.com/news/no202/28hotspot