Engineering topics

Wilson, Robert M.

Publications and source records attributed to Wilson, Robert M..

At least 91 records · Page 5

NASA NTRS1998

Trends in the Annual Frequency of Atlantic Basin Intense Hurricanes: Implications for the Near-Term

During the interval of 1944-1997, 120 intense hurricanes (category 3, 4, or 5 on the Saffir-Simpson hurricane scale) have been observed in the Atlantic basin. These intense hurricanes have had an observed annual frequency of 0-7 events per year (having a mean, mode, and median equal to about 2 events per year), being preferentially lower during El Ninio years and higher during non-El Ninio years. Also, it has recently been established that a long-term downward trend in the annual frequency of intense hurricanes, spanning about five decades, has taken place, although this trend can, alternatively, be explained as a shift from a more active state prior to the mid 1960's to a less active state thereafter (rather than as a simple linear decline). In this paper, on the basis of 10-yr moving averages, the long4erm trend of the frequency of intense hurricanes is compared against one for the annual mean temperature at Armagh Observatory, Northern Ireland (which serves as a proxy for climatic change). Interestingly, the two sets of 10-yr moving averages correlate extremely well, especially, when incorporating a slight 6-yr lag between them (with temperature leading; r = 0.90). This suggests that the current leading trend of temperature, which had been downward, but now is upward, may portend a return to the more active state for intense hurricanes. Thus, the 1998 season (presuming the abatement of El Ninio prior to the start of the hurricane season), and for several years thereafter (at least, into the early years of the next millennium), may have an annual frequency of intense hurricanes that is commensurate with the previously observed active state that was seen prior to the mid 1960's. If true, then, the shift to the more active state, probably, occurred in the mid-to-late 1980's, apparently, having gone undetected because of the masking, or modulating, effect of El Ninio, which has been rampant since the mid-to-late 1980's.

Wilson, Robert M.↗

NASA NTRS1998

A Comparison of Wolf's Reconstructed Record of Annual Sunspot Number with Schwabe's Observed Record of Clusters of Spots for the Interval of 1826-1868

Samuel Heinrich Schwabe, the discoverer of the sunspot cycle, observed the Sun routinely from Desau, Germany during the interval of 1826-1869, averaging about 290 observing days per year. His yearly counts of 'clusters of spots' (or, more correctly, the yearly number of newly appearing sunspot groups) provided a simple means for describing the overt features of the sunspot cycle (i.e., the timing and relative strengths of cycle minimum and maximum). In 1848, Rudolf Wolf, a Swiss astronomer, having become aware of Schwabe's discovery, introduced his now familiar 'relative sunspot number' and established an international cadre of observers for monitoring the future behavior of the sunspot cycle and for reconstructing its past behavior (backwards in time to 1818, based on daily sunspot number estimates). While Wolf's reconstruction is complete (without gaps) only from 1849 (hence, the beginning of the modern era), the immediately preceding interval of 1818-1848 is incomplete, being based on an average of 260 observing days per year. In this investigation, Wolf's reconstructed record of annual sunspot number is compared against Schwabe's actual observing record of yearly counts of clusters of spots. The comparison suggests that Wolf may have misplaced (by about 1-2 yr) and underestimated (by about 16 units of sunspot number) the maximum amplitude for cycle 7. If true, then, cycle 7's ascent and descent durations should measure about 5 years each instead of 7 and 3 years, respectively, the extremes of the distributions, and its maximum amplitude should measure about 96 instead of 70. This study also indicates that cycle 9's maximum amplitude is more reliably determined than cycle 8's and that both appear to be of comparable size (about 130 units of sunspot number) rather than being significantly different. Therefore, caution is urged against the indiscriminate use of the pre-modern era sunspot numbers in long-term studies of the sunspot cycle, since such use may lead to specious results.

Wilson, Robert M.↗

NASA NTRS1998

Comment on the Predicted Size of Cycle 23 Based on the Inferred Three-Cycle Quasi-Periodicity of the Planetary Index Ap

Recently, Ahluwalia [1998] reviewed the solar and geomagnetic data for the last 6 decades and remarked that these data "indicate the existence of a three-solar-activity-cycle quasi-periodicity in them." Futhermore, on the basis of this inferred quasi-periodicity, he asserted that cycle 23 represents the initial cycle in a new 3-cycle string, implying that it "will be more modest (a la cycle 17) with an annual mean sunspot number count of 119.3 +/- 30 at the maximum," a prediction that is considerably below the consensus prediction of 160 +/- 30 by Joselyn et al. [1997] and of similar predictions by others based on a variety of predictive techniques. Several major sticking points of Ahluwalia's presentation, however, must be redressed, and these issues form the basis of this comment. In particular, it is shown that Ahluwalia used inappropriate values of the Ap index in his analysis, that the inferred 3-cycle relationship which Ahluwalia claims for both Ap and SSN does not exist for the previous 6-cycle interval (prior to cycle 17) for SSN, that his inferred fit is only of marginal statistical significance (having r = 0.81), and that two alternative precursor fits (both with r = 0.96 or greater) exist which strongly suggest that R max for cycle 23 will be much larger than forecast by Ahluwalia (namely, about 168-187). Thus, caution must be exercised in accepting Ahluwalia's findings.

Hathaway, David H.↗

NASA NTRS1998

Statistical Aspects of Intense Hurricanes in the Atlantic Basin during the Past 49 Hurricane Seasons (1950-1998)

Statistical aspects of intense hurricanes (those of category 3 or higher) in the Atlantic basin for the interval of 1950-1998 are investigated with respect to the ENSC, cycle and the postulated 'more versus less' activity modes for intense hurricane activity. This is accomplished in order to evaluate the statistical basis for these specific groupings and to presage a forecast for the number of expected intense hurricanes during the forthcoming 1999 hurricane season. Statistically speaking, because the 1998-1999 La Nina (onset presumed to be September 1998) should persist longer than about a year - the average duration for La Nina events based on the 10 previously occurring La Nina, each having a duration in the range of 7-22 months - it seems likely that the 1999 season will be classified as a 'non-El Nino-related' (NENR) season. If true, then, greater than or equal to 2 intense hurricanes are to be expected. Based on Poisson statistics, the probability of greater than or equal to 2 events is about 77% when the season is classified as NENR, and it is about 87% when the season is classified as NENR and the 'more active' phase is in fashion; likewise, the probability of greater than or equal to 4 events is about 31% and 48%, respectively, for the two cases. Therefore, an above average rate (possibly, as many as 4 +/- 1, or higher) of intense hurricanes forming in the Atlantic basin seems a very distinct possibility during the 1999 season.

Wilson, Robert M.↗

NASA NTRS1998

Estimating the Size and Timing of Maximum Amplitude for Cycle 23 from Its Early Cycle Behavior

On the basis of the lowest observed smoothed monthly mean sunspot number, cycle 23 appears to have conventionally begun in May 1996, in conjunction with the first appearance of a new cycle, high-latitude spot-group. Such behavior, however, is considered rather unusual, since, previously (based upon the data- available cycles 12-22), the first appearance of a new cycle, high-latitude spot- group has always preceded conventional onset by at least 3 months. Furthermore, accepting May 1996 as the official start for cycle 23 poses a dilemma regarding its projected size and timing of maximum amplitude. Specifically, from the max-min and amplitude-period relationships we infer that cycle 23 should be above average in size and a fast riser, with maximum amplitude occurring before May 2000 (being in agreement with projections for cycle 23 based on precursor information), yet from its initial languid rate of rise (during the first 6 months of the cycle) we infer that it should be below average in size and a slow riser, with maximum amplitude occurring after May 2000. The dilemma vanishes, however, when we use a slightly later-occurring onset. For example, using August 1996, a date associated with a local secondary minimum prior to the rapid rise that began shortly thereafter (in early 1997), we infer that cycle 23's rate of rise is above that for the mean of cycles 1-22, the mean of cycles 10-22 (the modern era cycles), the mean of the modern era'fast risers,' and the largest of the modern era 'slow risers' (i.e., cycle 20), thereby, suggesting that cycle 23 will be both fast-rising and above average in size, peaking before August 2000. Additionally, presuming cycle 23 to be a well- behaved fast-rising cycle (regardless of whichever onset date is used), we also infer that its maximum amplitude likely will measure about 144.0 q+/- 28.8 (from the general behavior found for the bulk of modern era fast risers; i.e., 5 of 7 have had their maximum amplitude to lie within 20% of the mean curve for modern era fast risers). It is apparent, then, that sunspot number growth during 1998 will prove crucial for correctly establishing the size and shape of cycle 23.

Wilson, Robert M.↗

NASA NTRS1997

Gauging the Nearness and Size of Cycle Minimum

By definition, the conventional onset for the start of a sunspot cycle is the time when smoothed sunspot number (i.e., the 12-month moving average) has decreased to its minimum value (called minimum amplitude) prior to the rise to its maximum value (called maximum amplitude) for the given sunspot cycle. On the basis (if the modern era sunspot cycles 10-22 and on the presumption that cycle 22 is a short-period cycle having a cycle length of 120 to 126 months (the observed range of short-period modern era cycles), conventional onset for cycle 23 should not occur until sometime between September 1996 and March 1997, certainly between June 1996 and June 1997, based on the 95-percent confidence level deduced from the mean and standard deviation of period for the sample of six short-pei-iod modern era cycles. Also, because the first occurrence of a new cycle, high-latitude (greater than or equal to 25 degrees) spot has always preceded conventional onset of the new cycle by at least 3 months (for the data-available interval of cycles 12-22), conventional onset for cycle 23 is not expected until about August 1996 or later, based on the first occurrence of a new cycle 23, high-latitude spot during the decline of old cycle 22 in May 1996. Although much excitement for an earlier-occurring minimum (about March 1996) for cycle 23 was voiced earlier this year, the present study shows that this exuberance is unfounded. The decline of cycle 22 continues to favor cycle 23 minimum sometime during the latter portion of 1996 to the early portion of 1997.

Wilson, Robert M.↗

NASA NTRS1997

A Comparison of Wolf's Reconstructed Record of Annual Sunspot Number with Schwabe's Observed Record of 'Clusters of Spots' for the Interval of 1826-1868

On the basis of a comparison of Wolf s reconstructed record of yearly averages of sunspot number against Schwabe's observations of yearly counts of 'clusters of spots' (i.e., the yearly number of newly appearing sunspot groups) during the interval of 1826-1868, one infers that Wolf probably misplaced and underestimated the maximum amplitude for cycle 7. In particular, Schwabe's data suggest that the maximum amplitude for cycle 7 occurred in 1828 rather than in 1830 and that it measured about 86.3 (+/-13.9; i.e., the 90% confidence level) rather than 70.4. If true, then, the ascent and descent durations for cycle 7 should be 5 years each instead of 7 and 3 years, respectively. Likewise, on the basis of the same comparison, one infers that the maximums for cycles 8 and 9, occurring, respectively, in 1837 and 1848, were of comparable size (approximately 130), although, quite possibly, the one for cycle 8 may have been smaller. Lastly, presuming the continued action of the 'odd-even' effect (i.e., the odd-numbered following cycle of Hale even-odd cycle pairs having a maximum amplitude that is of comparable or larger size than the even-numbered leading cycle) during the earlier pre-modem era of cycles 6-9, one infers that Wolf's estimate for the size of cycle 6 probably is too low.

Wilson, Robert M.↗

NASA NTRS1996

Prelude to Cycle 23: The Case for a Fast-Rising, Large Amplitude Cycle

For the common data-available interval of cycles 12 to 22, we show that annual averages of sunspot number for minimum years (R(min)) and maximum years (R(max)) and of the minimum value of the aa geomagnetic index in the vicinity of sunspot minimum (aa(min)) are consistent with the notion that each has embedded within its respective record a long-term, linear, secular increase. Extrapolating each of these fits to cycle 23, we infer that it will have R(min) = 12.7 +/- 5.7, R(max) = 176.7 +/- 61.8, and aa(min) = 21.0 +/- 5.0 (at the 95-percent level of confidence), suggesting that cycle 23 will have R(min) greater than 7.0, R(max) greater than 114.9, and aa(min) greater than 16.0 (at the 97.5-percent level of confidence). Such values imply that cycle 23 will be larger than average in size and, consequently (by the Waidmeier effect), will be a fast riser. We also infer from the R(max) and aa(min) records the existence of an even- odd cycle effect, one in which the odd-following cycle is numerically larger in value than the even-leading cycle. For cycle 23, the even-odd cycle effect suggests that R(max) greater than 157.6 and aa(min) greater than 19.0, values that were recorded for cycle 22, the even-leading cycle of the current even-odd cycle pair (cycles 22 and 23). For 1995, the annual average of the aa index measured about 22, while for sunspot number, it was about 18. Because aa(min) usually lags R(min) by 1 year (true for 8 of 11 cycles) and 1996 seems destined to be the year of R(min) for cycle 23, it may be that aa(min) will occur in 1997, although it could occur in 1996 in conjunction with R(min) (true for 3 of 11 cycles). Because of this ambiguity in determining aa(min), no formal prediction based on the correlation of R(max) against aa(min), having r = 0.90, or of R(max) against the combined effects of R(min) and aa(min)-the bivariate technique-having r = 0.99, is possible until 1997, at the earliest.

Wilson, Robert M.↗

NASA NTRS1996

On Determining the Rise, Size, and Duration Classes of a Sunspot Cycle

The behavior of ascent duration, maximum amplitude, and period for cycles 1 to 21 suggests that they are not mutually independent. Analysis of the resultant three-dimensional contingency table for cycles divided according to rise time (ascent duration), size (maximum amplitude), and duration (period) yields a chi-square statistic (= 18.59) that is larger than the test statistic (= 9.49 for 4 degrees-of-freedom at the 5-percent level of significance), thereby, inferring that the null hypothesis (mutual independence) can be rejected. Analysis of individual 2 by 2 contingency tables (based on Fisher's exact test) for these parameters shows that, while ascent duration is strongly related to maximum amplitude in the negative sense (inverse correlation) - the Waldmeier effect, it also is related (marginally) to period, but in the positive sense (direct correlation). No significant (or marginally significant) correlation is found between period and maximum amplitude. Using cycle 22 as a test case, we show that by the 12th month following conventional onset, cycle 22 appeared highly likely to be a fast-rising, larger-than-average-size cycle. Because of the inferred correlation between ascent duration and period, it also seems likely that it will have a period shorter than average length.

Wilson, Robert M.↗

NASA NTRS1996

On the Importance of Cycle Minimum in Sunspot Cycle Prediction

The characteristics of the minima between sunspot cycles are found to provide important information for predicting the amplitude and timing of the following cycle. For example, the time of the occurrence of sunspot minimum sets the length of the previous cycle, which is correlated by the amplitude-period effect to the amplitude of the next cycle, with cycles of shorter (longer) than average length usually being followed by cycles of larger (smaller) than average size (true for 16 of 21 sunspot cycles). Likewise, the size of the minimum at cycle onset is correlated with the size of the cycle's maximum amplitude, with cycles of larger (smaller) than average size minima usually being associated with larger (smaller) than average size maxima (true for 16 of 22 sunspot cycles). Also, it was found that the size of the previous cycle's minimum and maximum relates to the size of the following cycle's minimum and maximum with an even-odd cycle number dependency. The latter effect suggests that cycle 23 will have a minimum and maximum amplitude probably larger than average in size (in particular, minimum smoothed sunspot number Rm = 12.3 +/- 7.5 and maximum smoothed sunspot number RM = 198.8 +/- 36.5, at the 95-percent level of confidence), further suggesting (by the Waldmeier effect) that it will have a faster than average rise to maximum (fast-rising cycles have ascent durations of about 41 +/- 7 months). Thus, if, as expected, onset for cycle 23 will be December 1996 +/- 3 months, based on smoothed sunspot number, then the length of cycle 22 will be about 123 +/- 3 months, inferring that it is a short-period cycle and that cycle 23 maximum amplitude probably will be larger than average in size (from the amplitude-period effect), having an RM of about 133 +/- 39 (based on the usual +/- 30 percent spread that has been seen between observed and predicted values), with maximum amplitude occurrence likely sometime between July 1999 and October 2000.

Wilson, Robert M.↗

NASA NTRS1996

On the Relationship Between Transit Velocity of Interplanetary Shocks and Solar Active Processes

Recently, it was reported that preferential relationships exist between the transit velocity V(sub T) of earthward-directed interplanetary shocks and solar active processes, in particular, eruptive filaments outside active regions (the size of the erupting filament L(sub f)) and solar flares (the value of the X-ray characteristic J). Unfortunately, statistical testing of the proposed associations was not accomplished, nor was the 'geo-effectiveness' of the events adequately described. Reported here are the results of a re-examination of the 21 eruptive filaments (SSC-EF events) and 26 X-ray flares (SSC-F events) that have been associated with storm sudden commencements (SSCs) at Earth. Simple statistical testing refutes the claim that a preferential relationship exists between V(sub T) and L(sub F), while it supports the claim that one exists between V(sub T) and J. More importantly, the inferred relationship between V(sub T) and J is found to be more complicated than previously thought. In particular, it now appears that SSC-F events may be separable into two groups, based on the value of J: a low-J group (J less than 56), in which V(sub T) varies directly with J, and a high-J group (J greater than 56), in which V(sub T) varies inversely with J. As a whole, high-J events are associated with shocks of higher average transit velocity than those of low-J events, and SSC-F events with shocks of higher average transit velocity than those of SSC-EF events. Further, high-J events tend to be of greater X-ray class ( greater than M3), longer duration (greater then 80 min), and are more likely to be associated with type II/IV radio emission (9 of 12) than low-J events. They also tend to occur in magnetically complex (gamma/delta configuration) active regions (10 of 12) that are large in area extent (area greater than 445 millionths of a solar hemisphere) on the day of flaring (9 of 12). Of the 9 solar proton events that affected the Earth's environment that were found to be associated with SSC-F events, six were high-J events. Concerning 'geo-effectiveness', there appears to be no preferential relationship between the value of the J-parameter and the most negative value of the Dst geomagnetic index Dst(min) following the SSC, which is found to usually occur at 6-14 h after SSC onset (18 of 26) and which ranged in value from -1 to -249 (having a median value of about -75). Of the 26 SSC-F events, only 14 can be associated with a Dst(min) less than or equal to -75, and of these only 7 were high-J events. Of the 14 storm-related events (i.e. Dst(min) less than or equal to -75), three have previously been identified as being either 'magnetic clouds' or 'bidirectional flows', both manifestations of earthward-directed coronal mass ejections (CMEs). Superposed epoch analyses of selected solar wind parameters and Dst during the interval of storm-related SSC-F events demonstrate that geoeffective SSC-F events tend to be associated with solar wind flows that are faster, greater in magnetic field strength, and have a rotating field which has a strong southward component shortly after SSC onset, in comparison to SSC-F events that do not have Dst(min) less than or equal to 75. Therefore, it is inferred that geoeffective SSC-F events are probably fast earthward-directed CMEs. Although no single parameter is found that can serve as a predictor of high-skill level for determining the geoeffectiveness of an SSC-F event prior to its occurrence at Earth, one finds that knowledge of the flare's hemispheric location and appearance or lack of appearance of a two-ribbon structure is sufficient to correctly predict the geoeffectiveness of 20 out of 25 of the SSC-F events (80%). Surprisingly, the association or lack of association of metric type II/IV radio emission as a characteristic for determining the geoeffectiveness of the SSC-F events proved unfruitful, as did, to a lesser extent, the duration of the X-ray emission.

Wilson, Robert M.↗

NASA NTRS1994

The shape of the sunspot cycle

The temporal behavior of a sunspot cycle, as described by the International sunspot numbers, can be represented by a simple function with four parameters: starting time, amplitude, rise time, and asymmetry. Of these, the parameter that governs the asymmetry between the rise to maximum and the fall to minimum is found to vary little from cycle to cycle and can be fixed at a single value for all cycles. A close relationship is found between rise time and amplitude which allows for a representation of each cycle by a function containing only two parameters: the starting time and the amplitude. These parameters are determined for the previous 22 sunspot cycles and examined for any predictable behavior. A weak correlation is found between the amplitude accurate to within about 30% right at the start of the cycle. As the cycle progresses, the amplitude can be better determined to within 20% at 30 months and to within 10% at 42 months into the cycle, thereby providing a good prediction both for the timing and size of sunspot maximum and for the behavior of the remaining 7-12 years of the cycle.

Hathaway, David H.↗

NASA NTRS1994

A comment on the suspected solar neutrino -- solar activity connection

Recently, it has been proposed that there exists a highly statistically significant (at greater than or equal to 98% level of confidence) relationship between Ar-37 production rate (namely, solar neutrinos) and the Ap geomagnetic index (namely, solar particles), based on the chi-square goodness-of-fit test and correlation analysis, for the interval 1970-1990. While a relationship between the two parameters, indeed, seems to be discernible, the strength of the relationship has been overstated. Instead of being significant at the afore-mentioned level of confidence, the relationship is found to be significant at only greater than or equal to 95% level of confidence, based on Yates' modification to the chi-square test for 2 x 2 contingency tables. Likewise, while correlation analysis yields a value of r = 0.2691, it is important to note that such a value suggests that only about 7% of the variance can be 'explained' by the inferred correlation and that the remaining 93% of the variance must be attributed to other sources.

Wilson, Robert M.↗

NASA NTRS1994

On the relationship between sunspots number and the flare index

During the years 1976-1991, sunspot number and the Kleczek flare index have displayed a strong linear correlation (r = 0.94), one that can be described by the equation y = -0.15 + 0.10 x, where x denotes annual sunspot number. While true, the temporal behaviors of the two parameters have differed, with sunspot number peaking first in 1979 and the flare index peaking much later in 1982 during cycle 21 and with more contemporaneous behavior in cycle 22 (both peaking in 1989, with a secondary peak in 1991). The difference appears to be directly attributable to the way in which the Kleczek flare index has been defined; namely, the annual flare index is the sum of the product of each flare's intensity (importance) times its duration (in minutes) divided by the total number of flares during the year. Because the number of 'major' flares (those of importance greater than or equal to 2) and flares of very long duration (duration greater than or equal to 100 min) both peaked after sunspot maximum (1982/81, respectively) in cycle 21, one should have expected the flare index to also peak (which it did). Likewise, because the number of major flares and flares of very long duration peaked simultaneously with sunspot number (1989) in cycle 22, one should have expected the flare index to also peak (which it did).

Wilson, Robert M.↗

NASA NTRS1994

A Comment on the Suspected Solar Neutrino-Solar Activity Connection

Recently, it has been proposed that there exists a highly statistically significant (at greater than or equal to 98% level of confidence) relationship between Ar-37 production rate (viz., solar neutrinos) and the Ap geomagnetic index (viz., solar particles), based on the (chi)-square goodness-of-fit test and correlation analysis, for the interval 1970-1990. While a relationship between the two parameters, indeed, seems to be discernible, the strength of the relationship has been overstated. Instead of being significant at the afore-mentioned level of confidence, the relationship is found to be significant at only greater than or equal to 95% level of confidence, based on Yates' modification to the (chi)-square test for 2 x 2 contingency tables. Likewise, while correlation analysis yields a value of r = 0.2691, it is important to note that such a value suggests that only about 7% of the variance can be 'explained' by the inferred correlation and that the remaining 93% of the variance must be attributed to other sources.

Wilson, Robert M.↗

NASA NTRS1993

On the variation of the sun's X ray background flux and its relation to the sun's flaring rate, energetic event rate, and the solar cycle

Daily averages of the sun's X-ray background flux as measured by the GOES satellite are combined to yield monthly means and 'smoothed' monthly means (12-month moving averages) for the interval January 1986 through May 1992 (minimum rise, maximum, and initial decline of solar cycle 22). These averages are then compared directly to the sun's optical flaring rate, energetic event rate, and the usual markers of the solar cycle (e.g., sunspot number, total corrected sunspot area, and 10.7-cm solar radio flux, number of groups, and number of spots). The results of this analysis support previous findings that there exists a remarkably close positive relationship between the optical flaring rate and the X-ray background flux rate (the independent variable), and that the X-ray background flux rate can be used as a proxy for the solar cycle. Additionally, this study has found that a strong positive relationship exists between the energetic event rate and the X-ray background flux rate (the independent variable), and that the lag between the maxima of the rates of optical flaring and X-ray background flux reported for cycle 21 did not recur for cycle 22.

Wilson, Robert M.↗

NASA NTRS1993

A prediction for the onset of cycle 23

The present sunspot cycle (number 22) is now in decline, having had its onset in September 1986, its primary maximum in July 1989, and a secondary maximum (of lower value) in 1991. Dependent upon whether cycle 22 is a short-or 1ong-period cycle, onset for cycle 23 w/II occur, respectively, either prior or subsequent to about July 1997. A relation is described, involving the slopes (i.e., the average rates of change in smoothed sunspot number values) as seen during the ascending and descending portions of the sunspot cycle, which appears to clarify, at least for cycle 22, the ambiguity of cycle length. In particular, the relation strongly suggests that cycle 22 is a short-period cycle and that onset for cycle 23 will come early rather than late, with the most probable date for cycle 23 onset being May-November 1996.

Wilson, Robert M.↗

NASA NTRS1992

On the variation of the Nimbus 7 total solar irradiance

For the interval December 1978 to April 1991, the value of the mean total solar irradiance, as measured by the Nimbus-7 Earth Radiation Budget Experiment channel 10C, was 1,372.02 Wm(exp -2), having a standard deviation of 0.65 Wm(exp -2), a coefficient of variation (mean divided by the standard deviation) of 0.047 percent, and a normal deviate z (a measure of the randomness of the data) of -8.019 (inferring a highly significant non-random variation in the solar irradiance measurements, presumably related to the action of the solar cycle). Comparison of the 12-month moving average (also called the 13-month running mean) of solar irradiance to those of the usual descriptors of the solar cycle (i.e., sunspot number, 10.7-cm solar radio flux, and total corrected sunspot area) suggests possibly significant temporal differences. For example, solar irradiance is found to have been greatest on or before mid 1979 (leading solar maximum for cycle 21), lowest in early 1987 (lagging solar minimum for cycle 22), and was rising again through late 1990 (thus, lagging solar maximum for cycle 22), having last reported values below those that were seen in 1979 (even though cycles 21 and 22 were of comparable strength). Presuming a genuine correlation between solar irradiance and the solar cycle (in particular, sunspot number) one infers that the correlation is weak (having a coefficient of correlation r less than 0.84) and that major excursions (both as 'excesses' and 'deficits') have occurred (about every 2 to 3 years, perhaps suggesting a pulsating Sun).

Wilson, Robert M.↗