We Aren't the Only Ones with Lousy Weather

 

Introduction to Earth/Mars Weather

Want to know what today's weather is like on Mars?

 

Space Weather's Connection to Solar Activity

Technological systems in space and on the Earth's surface are subject to adverse effects from solar driven space weather effects. The increasing deployment of radiation-, current-, and field-sensitive technological systems over the last few decades, the increasing complexity of interlocking components such as those represented by the national electric power grid, and the increasing presence of systems in space combine to make society more vulnerable to solar-terrestrial disturbances [ Allen and Wilkinson, 1993]. This has been emphasized by the large number of problems associated with the severe magnetic storms between 1989 and 1991 as the 11-year solar activity cycle peaked. This solar cycle (#22) maximum was greater than the past two, but not nearly as great as the cycle #19 maximum in 1958, when a coordinated effort was made to investigate the geophysical environment under the auspices of the International Geophysical Year (IGY). It was more comparable to the pre IGY cycle #18 which peaked in 1947. We now may anticipate a few years of lower activity as we approach solar minimum. However, of great concern are predictions of even greater activity than we have just experienced for the next solar maximum , which will be a typically mightier odd-numbered cycle, [i.e. Kopecký, 1991].

The cause of these disturbances is episodic energy and mass releases from the sun. Soft X-rays from a solar flare arrive within 10 minutes, creating ionization enhancements in the ionosphere. Energetic protons can arrive anywhere from a few minutes after the soft X-rays to hours later. Their arrival increases ionization in the polar ionosphere, increases the frequency of upsets in satellite electronics and begins solar panel degradation effects from the enhanced high energy fluxes. Depending on the speed of the solar wind, magnetic storms begin 1 to 2 days later when the shock wave impacts the earth's magnetosphere [see Cliver et al., 1990].

However, not all solar flares result in magnetic storms, and, even more significantly, not all storms can be associated with solar flares. While solar flares capture ones attention, coronal mass ejections (CMEs), sometimes associated with flares and sometimes not, now appear to be a primary cause of geomagnetic activity [ Kahler, 1992; Gosling, 1993]. CMEs are not easily detectable unless they occur on the limbs of the sun. CMEs that are ejected toward the Earth produce geomagnetic activity when the associated shock front arrives. The severity of the storm is related to the polarity of the north-south component of the interplanetary magnetic field (IMF) as well as the velocity of the solar wind. The distribution of effects is further influenced by the dawn-dusk component of the IMF. Prediction of geomagnetic storms based on observation of events on the Sun only will have a high degree of error, since we presently can not accurately model the direction of the interplanetary magnetic field and the speed of the disturbance.

Figure 1 shows the sequence of events leading up to the major magnetic storm of March 24, 1991 [ Shea and Smart, 1993]. The enhancement of the X-rays is followed by the solar proton enhancement and eventually the magnetic storm. The timing of some of the space weather related disruptions and events are shown at the bottom. On this storm a third radiation belt was injected between the inner and outer belts. Communication disruptions, power surges in ground transmission lines, satellite single event upsets and other effects are scattered throughout the time period. Aurora was seen as far south as Georgia. Admittedly, this was a major storm. But to a lesser degree, smaller storms exhibit these effects and present similar hazards.

A second factor in predicting geomagnetic activity and associate hazards is that within a major storm the magnetosphere releases energy to the high latitude ionosphere in episodic events called substorms. The triggering mechanism for substorms is not understood physically. Thus peaks in activity can occur at various times within the main storm. Substorms also occur on an a periodic routine basis during periods of moderate activity. These factors are reflected in the constantly changing AE (auroral electrojet) magnetic activity index, and are manifested in a highly variable ionosphere that impacts communications, navigation systems (LORAN and GPS) and the operation and tracking of low Earth-orbiting satellites.

Large magnetic storms can occur throughout the 11 year solar cycle, although they are more prevalent near solar maximum. In the declining phase of the solar cycle, recurrent moderate storms occur when high speed streams from particular regions on the sun rotate by the Earth with the 27 day solar rotation. These are accompanied by several days of very enhanced fluxes of energetic electrons in the outer radiation belt as observed at geosynchronous orbit. It was during one of these events in January, 1994, that control of the Canadian communications satellite Anik was lost. Thus, space weather hazards are always present but are, on average, more frequent and more intense near solar maximum.

 

Weather on Other Planets

Venus

Venus is Earth's nearest neighbour, and of all the planets is also the nearest in terms of size and density. However, people would find life on the surface of Venus very unpleasant. The atmosphere is composed mostly of carbon dioxide with clouds of sulfuric acid, while surface temperatures of 470 C with air pressures of up to 90 times that of Earth(equivalent to that found at a depth of 900 m beneath the ocean's surface) were measured by the Soviet Union's Venera-7 spacecraft which was able to transmit data from the surface of Venus in 1970 for 20 minutes before being destroyed. More recent spacecraft were able to map the surface of Venus from orbit to a resolution of 750 m.

Jupiter

The largest planet in the solar system, Jupiter's atmosphere is also home to the largest storms known in the solar system. Jupiter's Great Red Spot is a massive cyclone that would cover three Earths. The Great Red Spot's center has the puffy appearance generally associated with little or no wind and cloud motion, while its outer rim shows the streamlined shapes of 360 kilometer-per-hour winds. At the middle right of the frame is one of several white oval storms seen on Jupiter from Earth. The smallest details that can be see in this image are about 95 kilometers across.

 

 

 

These NASA Hubble Space Telescope views provide the most detailed complete global coverage of the red planet Mars ever seen from Earth. The pictures were taken on February 25, 1995, when Mars was at a distance of 65 million miles (103 million km).

To the surprise of researchers, Mars is cloudier than seen in previous years. This means the planet is cooler and drier, because water vapor in the atmosphere freezes out to form ice-crystal clouds. Hubble resolves Martian surface features with a level of detail only exceeded by planetary probes, such as impact craters and other features as small as 30 miles (50 kilometers) across.

Tharsis region

A crescent-shaped cloud just right of center identifies the immense shield volcano Olympus Mons, which is 340 miles (550 km) across at its base. Warm afternoon air pushed up over the summit forms ice-crystal clouds downwind from the volcano. Farther to the east (right) a line of clouds forms over a row of three extinct volcanoes which are from north to south: Ascraeus Mons, Pavonis Mons, Arsia Mons. It's part of an unusual, recurring "W"-shaped cloud formation that once mystified earlier ground-based observers.

 

Valles Marineris region

The 16 mile-high volcano Ascraeus Mons pokes through the cloud deck along the western (left) limb of the planet. Other interesting geologic features include (lower left) Valles Marineris, an immense rift valley the length of the continental United States. Near the image center lies the Chryse basin made up of cratered and chaotic terrain. The oval-looking Argyre impact basin (bottom) appears white due to clouds or frost.

 

Syrtis Major region

The dark "shark fin" feature left of center is Syrtis Major. Below it the giant impact basin Hellas. Clouds cover several great volcanos in the Elysium region near the eastern (right) limb. As clearly seen in the Hubble images, past dust storms in Mars' southern hemisphere have scoured the plains of fine light dust and transported the dust northward. This leaves behind a relatively coarser, and less reflective sand in, predominantly, the southern hemisphere.

 

SPRINGTIME ON MARS: HUBBLE'S BEST VIEW OF THE RED PLANET

This NASA Hubble Space Telescope view of the planet Mars is the clearest picture ever taken from Earth, surpassed only by close-up shots sent back by visiting space probes. The picture was taken on February 25, 1995, when Mars was at a distance of approximately 65 million miles (103 million km) from Earth.

Because it is spring in Mars' northern hemisphere, much of the carbon dioxide frost around the permanent water-ice cap has sublimated, and the cap has receded to its core of solid water-ice several hundred miles across. The abundance of wispy white clouds indicates that the atmosphere is cooler than seen by visiting space probes in the 1970s. Morning clouds appear along the planet's western (left) limb. These form overnight when Martian temperatures plunge and water in the atmosphere freezes out to form ice-crystal clouds.

Towering 16 miles (25 km) above the surrounding plains, volcano Ascraeus Mons pokes above the cloud deck near the western or limb. This extinct volcano, measuring 250 miles (402 km) across, was discovered in the early 1970s by Mariner 9 spacecraft. Other key geologic features include (lower left) the Valles Marineris, an immense rift valley the length of the continental United States. Near the center of the disk lies the Chryse basin made up of cratered and chaotic terrain. The oval-looking Argyre impact basin (bottom), appears white due to clouds or frost.

Seasonal winds carry dust to form striking linear features reminiscent of the legendary Martian "canals". Many of these "wind streaks" emanate from the bowl of these craters where dark coarse sand is swept out by winds. Hubble resolves several dozen impact craters down to 30-mile diameter. The dark areas, once misinterpreted as regions of vegetation by several early Mars watchers, are really areas of coarse sand that is less reflective than the finer, orange dust. Seasonal changes in the surface appearance occur as winds move the dust and sand around.

This picture was taken with Hubble's Wide Field Planetary Camera 2 in PC mode. Exposures were taken through three different color filters to create this true color image. The pictures were map-projected onto a sphere for accurate registration and perspective. Credit: Philip James (University of Toledo), Steven Lee (University of Colorado), NASA