From Andy May (2024): “Roger Pielke Jr. posted this plot (below) of the 3-year frequency of global major hurricanes (he uses a simple count of them) created by Ryan Maue (@RyanMaue). Dr. Maue also posted this plot on his twitter. Looks like an inverse sunspot plot and overlaid the SILSO monthly sunspot count. In the figure, the blue is Maue’s plot, and the orange is a plot of monthly SILSO sunspots. The correlation, or strictly speaking, the anti-correlation is obvious and very interesting. I don’t think Ryan Maue’s plot has been formally published yet.”
Here is my speculation:
It appears that some extreme weather here on Earth might be influenced by changes in solar activity. If the Svensmark cloud hypothesis is correct, increased solar activity deflects more Cosmic Rays (CR) away from the inner solar system producing less ionization in the troposphere, producing fewer clouds with more solar radiation reaching the oceans. Warming oceans leads to a greater temperature differential between the poles and the equator which promotes more hurricane activity. The oceans have a significant thermal lag – it takes time to heat and cool this huge mass of water so we see a time lag of about 3 years after solar maximum until the hurricane frequency reaches its maximum. As we approach solar minimum more CR ionization occurs producing more clouds and a cooling ocean. The pole/equator temperature differential then, begins to decline with hurricane frequency also decreasing.
How about the weather on the other planets in our solar system? Might it be influenced by galactic cosmic rays just like here on Earth? The clouds of Neptune captured by the Hubble Space Telescope were obtained over nearly 30 years over which is plotted the solar UV radiation during the solar cycle. We see maximum cloudiness at solar maximum. Just the opposite of the Svensmark hypothesis, which says maximum cloudiness should occur at solar minimum where CR intensity is maximum. Seems a paradox here.
This sequence of Hubble Space Telescope images chronicles the waxing and waning of cloud cover on Neptune. This nearly-30-year-long set of observations shows that the number of clouds grows increasingly following a peak in the solar cycle – where the Sun’s level of activity rhythmically rises and falls over an 11-year period. The Sun’s level of ultraviolet radiation is plotted in the vertical axis. The 11-year cycle is plotted along the bottom from 1994 to 2022. The Hubble observations along the top, clearly show a correlation between cloud abundance and solar peak of activity. One theory says that the increased ultraviolet radiation from the Sun, during its peak of activity, causes chemical changes deep in Neptune’s atmosphere. After a couple years this eventually percolates into the upper atmosphere to form clouds.
NASA, ESA, LASP, Erandi Chavez (UC Berkeley), Imke de Pater (UC Berkeley)
https://www.sciencedirect.com/science/article/abs/pii/S0019103523002440?via%3Dihub
Neptune’s atmosphere is made up mostly of hydrogen and helium with a bit of methane. The clouds are primarily composed of ammonia and methane. Temperatures are cold, around -170 C. Green and blue areas are where the red light from the sun is absorbed by methane. The planet has hundreds of times more methane, ethane and acetylene at the equator than at the poles. Ammonia ice, water ice, ammonia hydrosulfide, and methane ice are also present.
Just above Neptune’s rocky surface lies the troposphere. As altitude increases, temperature in the troposphere decreases. But in the next layer, the stratosphere, temperatures increase with altitude. This is related to the motion inside of the planet’s core, which heats Neptune more than the rays from the distant sun. The next layer is the thermosphere, where pressures are lower. The very outer edge of the atmosphere is known as the exosphere.
The clouds of Neptune vary with the altitude. Cold temperatures allow methane clouds to condense in the highest layers of the troposphere. Farther down where pressures are higher, clouds of hydrogen sulfide, ammonium sulfide, ammonia, and water could exist. Clouds of water-ice may be found at pressures of 50 bars, with clouds of hydrogen sulfide and ammonia beneath them.
Neptune also contains a couple of haze layers at very high altitudes of the troposphere and the stratosphere. These smog-like clouds are made up of hydrocarbons. Much like smog over major cities on Earth, the face of Jupiter has an umber tone which waxes and wanes. The lower stratosphere of Neptune is foggy because of the condensation of hydrocarbons such as acetylene and ethane. The thermosphere of Neptune is very high and hot. The temperature is around 750 K. Scientists haven’t figured out how this heat gets generated as Neptune is very far from the Sun and hard to observe in detail.
If Svensmark’s cloud hypothesis works on Earth it should work on Neptune. Here we see a reverse phase, where minimum cloudiness occurs at solar minimum. This concurrence brings maximum cosmic radiation which should promote more clouds not less. Something else might be going on here.
” High-energy galactic cosmic rays (CR)can penetrate to deep levels within Neptune’s atmosphere to form a substantial ionospheric layer in the lower stratosphere and upper troposphere of the planet. Because cosmic ray modulation in the interplanetary medium creates an inverse relationship between cosmic-ray intensity and solar activity, the ionization rate in the lower atmosphere will vary with the 11-year solar cycle in such a way that maximum ionization will occur at sunspot minimum and minimum ionization at sunspot maximum. This variable ionization may, by the process of ion-induced nucleation, regulate the formation and optical properties of an upper tropospheric haze in the atmosphere of Neptune and could thus provide a mechanism for modulating the planet’s visual brightness over a solar cycle.”
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/GL016i012p01489
Both clouds and haze may be formed by a UV photochemical reaction, cosmic ray-initiated reactions or both. As the sun gets more active and builds up to its maximum, it begins to emit more powerful and intense ultraviolet (UV) light. It has been found that around two years after this UV emission begins, Neptune’s clouds begin to appear, indicating that this UV is perhaps responsible for cloud formation. The cloud-forming aerosols created by cosmic ray interactions are formed further down in the troposphere and may be slowly transported to higher altitudes within the atmosphere.
Question: During solar maximum, is solar UV light the primary catalyst for cloud condensation and responsible for the progress of the observed cloud modulation? Svensmark says that the cosmic radiation intensity at solar maximum is at the minimum thus producing less tropospheric aerosols and haze. At solar maximum we observe solar UV is at the maximum but assume centrality of CR in the creation of tropospheric haze which would then be significantly reduced. This would lead to increasing upper troposphere transparency revealing the clouds that had been there the whole time. It is not the clouds that are changing it is the modulation of the haze opacity by cosmic rays.
UV and CR exposure of the upper troposphere and stratosphere of Neptune ionizes methane which undergoes chemical reactions creating aerosols of complex hydrocarbons. These aerosols can form a complex network of obscuring haze. These aerosols can also act as cloud condensation nuclei which facilitate cloud formation. During high CR periods during the solar cycle (solar minimum) aerosol formation increases as the UV contribution decreases. During low CR periods (solar maximum) aerosol formation decreases while the UV contribution increases. White methane clouds predominate during solar maximum and disappear during solar minimum. If the haze is reduced during solar maximum the clouds would be revealed. The decreased CR during solar maximum generates significantly less aerosols in the troposphere decreasing the haze formation there. Cosmic Rays seem to be the primary driver of cloud and haze forming aerosols in the troposphere of Neptune.
Cosmic radiation induced ionization is the main mechanism for ionizing the lower atmosphere of Neptune. Their higher penetration power, in comparison with solar UV photons, allows cosmic rays to penetrate deep into the atmosphere, ionizing the neutral molecules and generating an ionosphere similar in magnitude to the ionosphere produced by solar radiation in the upper atmosphere. UV will be absorbed by the haze layers as it passes through the atmosphere, whereas highly energetic secondary cosmic rays, typically muons of several GeV, can readily penetrate the deep Neptunian troposphere.
Notes:
(above) Global-average temperature–pressure profile of the atmospheres of Uranus and Neptune, with major regions of the atmosphere labelled (modified from Moses et al. Thermochemical equilibrium prediction of the upper-tropospheric cloud structure on Uranus (modified from Hueso & Sánchez-Lavega. The predicted mass mixing ratios of condensable gases are shown as colored solid lines, and the maximum cloud density as solid black lines with color-shaded regions.