Solar Activity, Cosmic Rays, and Global Warming Alexis Wagener and Greg Edwards.
-
Upload
darlene-gibbs -
Category
Documents
-
view
219 -
download
0
Transcript of Solar Activity, Cosmic Rays, and Global Warming Alexis Wagener and Greg Edwards.
Solar Activity, Cosmic Rays, and Global Warming
Alexis Wagener and Greg Edwards
Cosmic Rays
• Very high energy particles
• Protons and light nuclei
• Origins are unclear, evidence suggests they are emitted from supernovae and galactic nuclei
Image (right) shows cosmic ray collision, resulting in “atmospheric cascade”
Heliosphere: region maintained by solar wind whose magnetic properties maintain a “bubble” against outside pressure of interstellar medium
Magnetosphere: area near astronomical unit where charged particles are controlled by objects magnetic field
Heliosphere and Magnetosphere
The Atmospheric Effects
Ionization is the process by which an atom or molecule gains or loses an electron, becoming charged and more reactive
Cosmic Rays cause ionization in the atmosphere, creating aerosols in the troposphere (the lowest 10km) which then act as Cloud Condensation Nuclei (CCN)
Coronal Mass EjectionsMassive burst of solar wind and magnetic fields being released into space
Magnetic field generated creates a temporary shield against cosmic rays
The image (right) depicts solar wind disrupting the Earth’s magnetosphere
Forbush DecreasesReductions of galactic cosmic rays for periods of hours or days
Occurs from a disruption in the Earth’s magnetosphere in a geomagnetic storm as solar winds reach the earth, repulsing charged particles from the Earth’s atmosphere
Cosmic Ray Variation vs. TimeRed: Oulu, FinlandGreen: Magadan, RussiaBlue: Inuvik, Canada
Solar Activity CycleOccur over 11 years, resulting in modulation of sunspots
Cycle is marked by variation of short-wave solar irradiance, and frequency of coronal mass ejections and solar flares Observed Number of Sunspots vs.
Time
Sunspots• Temporary phenomena
on the photosphere: observed as visibly dark spots
• Caused by intense magnetic activity
Images (above) of our Sun taken in December 2006. Note the two sunspots in close proximity, each having opposite magnetic orientation
Used to measure intensity of solar cycle since coronal mass ejections occur in magnetically active region surrounding sunspots
Special Sensor Microwave/Imager
Measures brightness temperatures at four frequencies (85, 37, 22, and 19 GHz)
Information within measurements allow for calculation of near-surface wind speed, columnar water vapor, columnar cloud liquid water, and precipitation
Digital Rendering of SSM/I scan geometry
Moderate Resolution Imaging Spectroradiometer
Launched into orbit by Nasa in 1999 on board Terra Satellite and 2002 on board Aqua Satellite
Instruments image entire Earth every 1-2 days using varying resolutions
Designed to provide measurement in large-scale global dynamics including cloud cover and radiation budget
Digital rendering of MODIS in orbit
Aerosol Robotic Network (AERONET)
Network of ground based photometers used to measure atmospheric aerosol properties
Measures radiances at fixed wavelengths to determine an average of the total aerosol column within the atmosphere CIMEL Sunphotometer
Neutron Monitors
Ground based detector used to measure high-energy particles striking the atmosphere
Measures by-products reaching the surface (such as neutrons) of atmospheric cascade caused by primary cosmic ray collision
Neutron Monitor in the Antarctic
Ion Chambers
Gas filled radiation detector used to measure ionization of atmosphere
Specifically designed lead shielded ion chambers are used to measure muon intensity
Depiction (right) of ion chamber measuring induced current from ionization of gaseous field
Observed Solar Activity TrendBlue: Beryllium-10 concentrationRed: Annual observed sunspots
The trend of increased solar activity correlates to increased atmospheric ionization
Beryllium-10 is formed in the atmosphere by cosmic ray collisionCorrelation between trends suggests solar activity is responsible for reduction in cosmic ray flux
Global Temperature and Cosmic Ray FluxGlobal Temperature Anomaly vs. Time
Cosmic Ray Intensity Decrease vs. Time Red:
percentage over Solar Activity CyclesBlue: mean percentage
Similar trend after 1980 suggests correlation between global temperature and cosmic rays
Supporting the theory - Svensmark et al.
Hypothesis: Forbush Decreases in Galactic Cosmic Rays lead to less liquid water in low-altitude clouds, causing global warming.
Coronal Mass Ejections (releasing magnetic plasma clouds) lead to Forbush decreases in Cosmic Ray intensity in the Earth’s Atmosphere
26 Solar Events, 1987-2007Forbush Decrease dates ranked by depression of ionization
Dates in bold denote dates for which AERONET data is available
There is observed to be a direct correlation between Forbush Decreases (of cosmic rays) and decreased ionization in the lower atmosphere
Response to Forbush DecreasesAerosol particles
Cloud Water content
Liquid water cloud fraction
IR-detected low cloud
Red Curves show % change in cosmic ray neutron counts
Cloud water content responds to the cosmic ray minimum 4 days later than the aerosol count, supporting the hypothesized mechanism
Comparison of Forbush Decrease effects
Negative slopes suggest that minima in clouds and aerosols deepen with the strength of Forbush Decrease events
Points represent individual Forbush Decrease events
Blue: weighted lines of best fit
Discussion and Conclusion● Large error bars may have masked Forbush Decrease effects● Other studies used more Forbush Decreases, however they
included weaker ones, with greater relative uncertainties● Timescales: Evidence suggests aerosol growth occurs over a
few hours, however some models suggest growth in the order of several days
This study claims to show evidence of a strong influence on aerosol levels and cloudiness from solar variability on a global scale.
Ahluwalia - Cosmic Ray Intensity VariationUsing data from multiple high-latitude ion chambers measuring muon intensity with similar voltage cutoffs, one data segment is generated for cosmic ray variation from 1937-1994
Measured ionization and cosmic ray intensity is juxtaposed with observed solar activity on same time-scale
Additional hypothesis for climate affect: Peak in solar activity leads low conductivity in atmosphere and build-up of electric field, resulting in higher frequency of thunderstorms and greater cloud cover
Ahluwalia Raw Data
Black lines: annual mean hourly values of muon intensity (.01% change) vs. Time
Top line: Ionization Chamber at Cheltenham/Fredericksburg (1937-72)
BottomLine: Ionization Chamber at Yakutsk (1953-54)
Similar trend in the overlapping years allowed data to be combined to one segment
Normalization Issues
Yakutsk 1965 data point is ~1.6% above 1954 data point, inconsistent with Fredericksburg and global neutron monitor data
Cosmic Ray modulation from 1957-65 is 1.11% greater for Yakutsk than Fredericksburg
Cosmic Ray Decrease (.01%) vs. Time
Data “filtering” begins to show new overall trend emerging
Normalized Data
1.11% is added to Yakutsk data points from 1953-63
Points are plotted to a common scale with normalization 100% in 1965
New data segment suggests trend in Cosmic Ray Decrease consistent with global temperature anomaly
Normalized Mean Decrease (.01%) vs. Time; Solar Activity max. and min. denoted by M and m, respectively
Correlation between Solar Activity Cycles and Cosmic Ray Intensity
Solar Activity Cycle juxtaposed with corresponding cosmic ray intensity
Solar Activity (Sunspots) vs. Cosmic Ray Intensity (% Decrease)
No significant correlation between amplitude of solar activity and amplitude of cosmic ray modulation
Damon and Laut - Statistical Errors
• Based on non-filtered results, observers created curves to show strong correlation between solar activity cycles and global temperatures
• Recent data points were found to be arithmetic errors, creating a discrepancy with the physical statistics
These errors in the data and subsequent analysis were not recognized widely in the literature and should not be used to draw conclusions between solar activity and global climate
Suggested Correlation Between Solar Cycle Length and Temperature Change
Original figures released in 1991
Blue line: filtered, partially filtered, and non-filtered data for solar cycle length (years) vs. Time
Red line: Northern Hemisphere surface temperature anomaly (degrees Celsius) vs. Time
Given range of cycle length and temperature anomaly suggests 95% correlation between trends
Adjusted Figures for Solar Cycle Length
Blue line: Solar Cycle Length (years) vs. Time
New figures released in 2000, suggesting same general curve
Points 3, 4 are the result of trivial arithmetic error
Though enough data is available for filtering of entire curve, final points are still not representation of the physical data
Correct Filtered Solar Cycle Length
Blue line: Solar Cycle Length (years) vs. Time
Points 0-4 have undergone correct filtering with data available through 2004
Recent trend shows relatively no change in solar cycle length and small correlation with temperature change
Solar Cycle and Temperature Change on Larger Timescale
Orange: Sunspot Cycle Length (years)
Red: Smoothing of SCL (years)
Green: Surface Temperature Anomaly (Mann et al., 1998)
Blue: Surface Temperature Anomaly (Jones and Moberg, 2003)
Larger timescale shows discrepancy between temperature and solar cycle length trends
Criticism on Svensmark1997: Svensmark and Friis-Christensen suggest a relationship between galactic cosmic rays and global cloud cover using data not representative of global values
1998: Svensmark releases update with correct data, contradicting the original hypothesis
2000: Marsh and Svensmark release new hypothesis suggesting relationship is between galactic cosmic rays and “low cloud cover,” not total cloud cover
RealClimate - Skepticism on Cosmic Ray and Low Cloud Relationship
Rejects Svensmark’s hypothesis on cosmic ray affecting low cloud cover, citing selective use of data and inconclusive results
Takes issue with inconsistency in findings aerosols and cloud water content reach minima ~5 and ~7 days after forbush decrease, respectively, but cloud water content also reaches minimum ~4 days after aerosol minimum
Cloud lifetime is in the order of hours: observational effects on clouds days after the event is not sensible
Statistical Criticism of Svensmark
Svensmark et al. take measurements from only 26 Forbush Decreases, signifying only 5 as strong events
Forbush Decreases were measured with .06 GV cutoff neutron monitor, also measuring low-energy particles
Gaussian smooth with width of 2 and maximum of 10 days may result in omission of significant results, since hypothesis suggests results are in the order of several days