Engineering topics

Reichmann, Edwin J.

Publications and source records attributed to Reichmann, Edwin J..

14 records

NASA NTRS2004

Erratum: Evidence That a Deep Meridional Flow Sets the Sunspot Cycle Period

An error was made in entering the data. This changes the results concerning the length of the time lag between the variations in the meridional flow speed and those in the cycle amplitude. The final paragraph on page 667 should read: Finally, we study the relationship between the drift velocities and the amplitudes of the hemisphere/cycles. We compare the drift velocity at the maximum of the cycle to the amplitude of that cycle for that hemisphere. There is a positive (0.5) and significant (95%) correlation between the two. However, an even stronger relationship is found between the drift velocity and the amplitude of the N + 2 cycle. The correlation is stronger (0.7) and more significant (99%), as shown. This relationship is suggestive of a "memory" in the solar cycle, again a property of dynamo models that use meridional circulation. Indeed, the two-cycle lag is precisely the relationship found by Charbonneau & Dikpati. This behavior is, however, more difficult to interpret, and we elaborate on this in the next section. In either case, these correlations only explain part of the variance in cycle amplitude (25% for the current cycle and 50% for the N + 2 cycle). Obviously, other mechanisms, such as variations in the gradient in the rotation rate, also contribute to the cycle amplitude variations. Our investigation of possible connections between drift rates and the amplitudes of the N + 1 and N + 3 cycles gives no significant correlations at these alternative time lags.

Hathaway, David H.↗

NASA NTRS2000

Status of Cycle 23 Forecasts

Forecasts for the amplitude of cycle 23 that were reported prior to the start of, the cycle covered a full range of, values from very small to very large. A forecast reached by the consensus of a panel of forecasters convened at the time of minimum in 1996 [Joselyn et al., 1997] suggested that this cycle would be much larger than average with the smoothed International Sunspot Number reaching a maximum of 160 +/- 30 in the middle of the year 2000. A recent survey of solar cycle prediction techniques [Hathaway et al., 1999] found that the two most reliable techniques for forecasting the cycle prior to its start give similar predictions for this cycle's maximum -- 154 +/- 26 and 153 +/- 33. Curve-fitting and regression techniques can be used with some confidence now that cycle 23 is well underway. These techniques indicate a more modest sunspot cycle with a maximum of 112 + 10 -- only slightly larger than average. The current (May 2000) prediction using the combined predictions from both precursors and curve-fitting gives a cycle amplitude of about 135 +/- 20. This is within the errors given by the consensus and the precursor technique predictions but very close to their lower bounds. Inspection of the characteristics of cycle 23 thus far indicates that in some respects this cycle is an outlier but in other respects it is quite normal.

Hathaway, David H.↗

NASA NTRS1999

A Synthesis of Solar Cycle Prediction Techniques

A number of techniques currently in use for predicting solar activity on a solar cycle timescale are tested with historical data. Some techniques, e.g., regression and curve fitting, work well as solar activity approaches maximum and provide a month-by-month description of future activity, while others, e.g., geomagnetic precursors, work well near solar minimum but only provide an estimate of the amplitude of the cycle. A synthesis of different techniques is shown to provide a more accurate and useful forecast of solar cycle activity levels. A combination of two uncorrelated geomagnetic precursor techniques provides a more accurate prediction for the amplitude of a solar activity cycle at a time well before activity minimum. This combined precursor method gives a smoothed sunspot number maximum of 154 plus or minus 21 at the 95% level of confidence for the next cycle maximum. A mathematical function dependent on the time of cycle initiation and the cycle amplitude is used to describe the level of solar activity month by month for the next cycle. As the time of cycle maximum approaches a better estimate of the cycle activity is obtained by including the fit between previous activity levels and this function. This Combined Solar Cycle Activity Forecast gives, as of January 1999, a smoothed sunspot maximum of 146 plus or minus 20 at the 95% level of confidence for the next cycle maximum.

Hathaway, David H.↗

NASA NTRS1999

A Survey and Synthesis of Solar Cycle Prediction Techniques

A number of techniques for predicting solar activity on a solar cycle time scale are identified, described, and tested with historical data. Some techniques, e.g. regression and curve-fitting, work well as solar activity approaches maximum and provide a complete description of future activity, while others, e.g. geomagnetic precursors, work well near solar minimum but only provide an estimate of the amplitude of the cycle. A synthesis of different techniques is shown to provide a more accurate and useful forecast of solar cycle activity levels. A combination of two uncorrelated geomagnetic precursor techniques provides the most accurate prediction for the amplitude of a solar activity cycle at a time well before activity minimum. This Combined Precursor Method gives a smoothed sunspot number maximum of 154+/-21 at the 95% level of confidence for the next cycle maximum. A mathematical function dependent upon the time of cycle initiation and the cycle amplitude then describes the level of solar activity for the next complete cycle. As the time of cycle maximum approaches a better estimate of the cycle activity is obtained by including the fit between previous activity levels and this function. This Combined Solar Cycle Activity Forecast gives, as of January 1999, a smoothed sunspot maximum of 146+/-20 at the 95% level of confidence for the next cycle maximum. The success of the geomagnetic precursors in predicting future solar activity suggests that solar magnetic phenomena at latitudes above the sunspot activity belts are linked to solar activity which occurs many years later in the lower latitudes.

Hathaway, David H.↗

NASA NTRS1998

On the Correlation Between Maximum Amplitude and Smoothed Monthly Mean Sunspot Number during the Rise of the Cycle (from t = 0-48 months Past Sunspot Minimum)

During the rise from sunspot minimum to maximum, the observed value of smoothed monthly mean sunspot number at maximum RM is found to correlate with increasing strength against the current value of smoothed monthly mean sunspot number R(t), where t is the elapsed time in months from minimum. On the basis of the modern era sunspot cycles (i.e., cycles 10-22), the inferred linear correlation is found to be statistically important (i.e., at the 95-percent level of confidence) from about 11 mo past minimum and statistically very important (i.e.. at the 99-percent level of confidence) from about 15 mo past minimum; ignoring cycle 19, the largest cycle of the modern era, the inferred linear correlation is found to be statistically important from cycle onset. On the basis of R(t), estimates of RM can be gauged usually to within about +/- 30 percent during the first 2 yr and to within about +/- 20 percent (or better) after the first 2 yr of a cycle's onset. For cycle 23, because controversy exists regarding the placement of its minimum (i.e., its onset), being either May 1996 or perhaps August 1996 (or shortly thereafter), estimates of its RM are divergent, being lower (more like a mean size cycle) when using the earlier epoch of minimum and higher (above average in size) when using the later-occurring minimum. For smoothed monthly mean sunspot number through October 1997 (t = 17 or 14 mo, respectively), having a provisional value of 32.0. the earlier minimum date projects an RM of 110.3 +/- 33.1, while the later minimum date projects one of 137.2 +/- 41.2. The projection is slowly decreasing in size using the earlier onset date, while it is slowly increasing in size using the later onset date.

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 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 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 NTRS1990

UBV photometry of the Ap variable UZ Psc = HD 10783

The photometric variability of the Ap star HD 10783 = UZ Psc is discussed. New UBV photometry, obtained between late 1965 and early 1969, is presented and it is combined with existing published photometry to derive an improved ephemeris for times of maximum brightness: 2439758.00 + 4d.1328 n. It is concluded that the results are not very sensitive to the small shifts applied to the blue photometry.

Hardie, Robert H.↗

NASA NTRS1989

Ultraviolet events observed in active regions. I - Observations and scenario

UV line data obtained in solar active regions on and near the limb, taken with the Ultraviolet Spectrometer and Polarimeter experiment on the Solar Maximum Mission are examined. The study provides insight into the physical processes behind sudden localized brightenings (or microflares) that occur within these active regions and their relation to surging activity. Time sequences of rasters and rasters through the line (taken in Ly-alpha and N V lines simultaneously) and C IV dopplergrams are the core of these data. They show the brightening events on the disk and Doppler shifts in dynamic events on the disk and above the limb. The study suggests, for the events, a localized energy deposition in a region of the chromosphere that heats the material and produces a pressure pulse. This mechanism explains the brightenings in transition region lines and also the observed surging behavior and jet-like events.

Fontenla, Juan M.↗

NASA NTRS1987

Lyman alpha SMM/UVSP absolute calibration and geocoronal correction

Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter (UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were analyzed and provide instrumental calibration details. Specific values of the instrument quantum efficiency, Lyman alpha absolute intensity, and correction for geocoronal absorption are presented.

Fontenla, Juan M.↗