Guest essay by David Archibald
“The atmosphere around Uranus is one of the coldest in the solar system, but still contains clouds and ice, like our own atmosphere here on Earth.
“The changing brightness of the planet shows that something is happening to the clouds. We have found that the change is caused by two processes.
“One is chemical, caused as fluctuating levels of UV sunlight alters the colour of particles in the atmosphere. The other is due to high-speed particles from outside the solar system, known as galactic cosmic rays, bombarding the atmosphere and influencing the formation of clouds.”
The scientists used data from telescopes on Earth, as well as cosmic rays measured by the Voyager 2 spacecraft, to make their assessment.
To put that solar effect into perspective, the following is a schematic representation of the relative distances of the Earth and Uranus from the Sun:
If the solar cycle affects the climate of Uranus then it could reasonably be expected to affect Earth’s climate. The solar irradiance hitting Uranus is 3.69 W/m2, what hits Earth is 368 times greater. Svensmark’s theory of clouds being affected by cosmic rays is eternal; to recap the the changing interplanetary field controls the flux of galactic cosmic rays reaching the Earth which in turn changes the neutron flux and production of nucleation sites for cloud droplets. Clouds reflect 40 percent of sunlight straight back into space; open ocean absorbs 95 percent so the amount of cloud cover controls global temperature as shown by this graphic:
Figure 1: Tropical cloud cover 15N – 15S and global air surface temperature 1983 – 2009
The cloud cover data in Figure 1 came from the International Satellite Cloud Climatology Project which stopped in 2009 which is a pity because it was showing good support for Svensmark’s theory. Despite the fact that Solar Cycle 24 is weaker than Solar Cycle 23 in terms of sunspot number and F10.7 flux, total solar irradiance has been as constant as the northern star as shown by the LASP data in Figure 2:
Figure 2: Total solar irradiance aligned on solar minimum
Figure 2 shows that the Sun in Solar Cycle 24 has been tracking Solar Cycle 23 closely for the last few years. Figure 3 shows that the interplanetary magnetic field has been backloaded for this cycle with a new high in activity after solar maximum:
Figure 3: Interplanetary Magnetic Field 1966 – 2017
The sum of the magnetic field, the flow density and flow speed produces the solar wind flow pressure:
Figure 4: Solar Wind Flow Pressure 1967 – 2017
Sunspot number and F10.7 flux may be weak but the solar wind flow pressure is back to the levels it held over Solar Cycle 23, with the jump up in activity from solar maximum in 2014. The next stage in the process is the neutron flux that initiates cloud formation:
Figure 5: Oulu Neutron Count 1964 – 2017
The neutron count is back to levels above that of recent solar minima and the 1970s cooling period. Until recently climate hasn’t followed in response. The eternal question is the length of the current cycle and thus the timing of the next solar minimum.
Figure 6: Heliospheric Current Sheet Tilt Angle aligned on solar minima
Figure 6 shows that Solar Cycle 24 (red line) is tracking along with Solar Cycles 21 and 22 which were strong, short cycles. But anything could happen. When the solar wind flow pressure finally collapses into solar minimum, the neutron flux should reach a new high for the instrument record.
David Archibald is the author of American Gripen: The Solution to the F-35 Nightmare