arXiv subjects

W. R. Webber

Publications and source records attributed to W. R. Webber.

40 records · Page 3Linked to original sources

arXiv2011

Voyagers 1 and 2 in a Shrunken and Squashed Heliosphere

We have extended our earlier calculations of the distance to the Heliospheric Termination Shock (HTS) - which covered the period from the launch of V1 and V2 in 1977 to 2005 - to the period from 2006 to 2011. During this latter period the solar wind speed, ram pressure and magnetic field decreased to the lowest levels in recent history, related to the sunspot minimum in 2008-2009. The HTS distance has decreased correspondingly so that V1, which was crossed by the HTS at 94 AU in late 2004, would now, in early 2011, be expected to reach the HTS at a distance ~80 AU, when the HTS distance would be expected to be at its minimum. Similarly V2, which was crossed by the HTS at 84 AU in mid 2007, would, in early 2011, reach the HTS at a distance of only 74 AU. These distances, in early 2011, are ~15% less than those at which V1 and V2 initially reached the HTS. The distance to the Heliopause (HP) is more uncertain but recent calculations place its equilibrium distance at between 1.4-1.6 times the HTS distance. Allowing for an additional 1 year for the HP to reach its equilibrium minimum distance relative to the HTS would mean that, assuming this distance remains a constant fraction larger than the HTS distance, the HP distance would be at its minimum distance of (1.4-1.6) x 80 AU = 112-128 AU at V1 in early 2012. At this time V1 will be at a distance of ~120 AU so that there is a possibility that V1 could cross the HP and enter interstellar space at the time 2012.0 \pm 1 year. If the crossing does not happen during this time period, then it is unlikely that V1 will reach this defining boundary before about 2016 because of the expected outward motion of the HTS and the HP towards their more normal distances of 85-96 and ~120 -140 AU coincident with the maximum of the new sunspot cycle.

astro-ph.SR↗

arXiv2010

A Comparison Of New Calculations Of The Yearly 10Be Production In The Earths Polar Atmosphere By Cosmic Rays With Yearly 10Be Measurements In Multiple Greenland Ice Cores Between 1939 And 1994 - A Troubling Lack Of Concordance Paper #2

We have compared the yearly production rates of 10Be by cosmic rays in the Earths polar atmosphere over the last 50-70 years with 10Be measurements from two separate ice cores in Greenland. These ice cores provide measurements of the annual 10Be concentration and 10Be flux levels during this time. The scatter in the ice core yearly data vs. the production data is larger than the average solar 11 year production variations that are being measured. The cross correlation coefficients between the yearly 10Be production and the ice core 10Be measurements for this time period are <0.4 in all comparisons between ice core data and 10Be production, including 10Be concentrations, 10Be fluxes and in comparing the two separate ice core measurements. In fact, the cross correlation between the two ice core measurements, which should be measuring the same source, is the lowest of all, only ~0.2. These values for the correlation coefficient are all indicative of a "poor" correlation. The regression line slopes for the best fit lines between the 10Be production and the 10Be measurements used in the cross correlation analysis are all in the range 0.4-0.6. This is a particular problem for historical projections of solar activity based on ice core measurements which assume a 1:1 correspondence. We have made other tests of the correspondence between the 10Be predictions and the ice core measurements which lead to the same conclusion, namely that other influences on the ice core measurements, as large as or larger than the production changes themselves, are occurring. These influences could be climatic or instrumentally based. We suggest new ice core measurements that might help in defining more clearly what these influences are and-if possible-to correct for them.

physics.geo-ph↗

arXiv2010

A comparison of new calculations of 10be production in the earths polar atmosphere by cosmic rays with 10be concentration measurements in polar ice cores between 1939-2005 - a troubling lack of concordance paper #1

Using new calculations of 10Be production in the Earths atmosphere which are based on direct measurements of the 11-year solar modulation effects on galactic cosmic rays and spacecraft measurements of the cosmic ray energy spectrum, we have calculated the yearly average production of 10Be in the Earths atmosphere by galactic and solar cosmic rays since 1939. During the last six 11-year cycles the average amplitude of these production changes is 36%. These predictions are compared with measurements of 10Be concentration in polar ice cores in both the Northern and Southern hemisphere over the same time period. We find a large scatter between the predicted and measured yearly average data sets and a low cross correlation ~0.30. Also the normalized regression line slope between 10Be production changes and 10Be concentration changes is found to be only 0.4-0.6; much less than the value of 1.0 expected for a simple proportionality between these quantities, as is typically used for historical projections of the relationship between 10Be concentration and solar activity. The distribution of yearly averages in the 10Be concentration level in the data from the Dye-3 ice core in Greenland for the time period 1939-1985, contains a "spike" of high concentration one year averages which is not seen in the production calculations. These and other features suggest that galactic cosmic ray intensity changes which affect the production of 10Be in the Earths atmosphere are not the sole source of the 10Be concentration changes and confirm the importance of other effects, for example local and regional climatic effects, which could be of the same magnitude as the 10Be production changes.

physics.geo-ph↗

arXiv2009

Two recent kHz outer heliospheric radio emissions seen at Voyager 1-What are the interplanetary events that trigger them and where are these events when the radio emissions start?

We have examined instigating events at the Sun that may be responsible for two of the most recent outer heliospheric kHz emissions detected by the University of Iowa plasma wave detector on Voyager 1 starting at 2004.64 and 2006.39, respectively. These interplanetary events have been followed outward from the Sun using plasma and cosmic ray data from Ulysses and Voyagers 1 and 2. For both intervals of kHz emissions, events originating near the Sun that turn out to be the most intense events in this 11-year solar cycle as observed by the plasma and cosmic ray variations in the outer heliosphere, reach V1 and V2 which are near the heliospheric termination shock at almost the same time that the two kHz radio emissions turn-on. These two events which originate near the Sun about 2003.89 (the 2003 Halloween event) and at 2005.71, are also unusual in that they develop solar wind ram pressure waves in the outer heliosphere with maximum pressures ~6-8 times the average solar wind pressure when they reach the heliospheric termination shock. We believe that this study suggests a possible new paradigm for the origin of these latest kHz emissions. This new paradigm is different from the current one describing earlier kHz events. It is related to the strength of these pressure waves in the outer heliosphere and involves the arrival of these large pressure waves at the heliospheric termination shock rather than the arrival of a shock at the heliopause as is the current paradigm.

physics.space-ph↗