January 5, 2004 To: Sue Greer Dan Wilkinson SOCC Suitland Fm: Dave Evans Re: General update I have finished the clean up and verification of NOAA-14, NOAA-15, NOAA-16, and NOAA-17 data from 2004 and have some updated performance information and figures that may be of interest. NOAA-12 We stopped archiving NOAA-12 SEM data as of July 2002. We continue to receive about one or two orbits of NOAA-12 data each day. Those data are processed as received and the results posted on the real-time web pages. However, those data are no longer archived. The assessment of the NOAA-12 SEM performance as of mid-2002 is contained in the 2002 SEM update memo and is not repeated here. NOAA-14 We terminated archive data processing of NOAA-14 as of January 1, 2005. This SEM, the last of the SEM-1 series, began operation in January 1995 and had been operating some 10 years. During 2004 SEC received about 90% of possible NOAA-14 data. We expect the SEM-2 on NOAA-18 to come on line in the spring of 2005 and, at that time, the data flow from NOAA-14 would likely to become still sparser. Data from the SEM on NOAA-14 will still be processed for the real-time web displays as that data arrives, as is done also for the relatively rare orbits of NOAA-12 data. The state of the MEPED solid-state detector telescopes in the NOAA-14 SEM remains the same as of January 1, 2004 and that performance is summarized below. All three operating solid-state detector telescopes have had noisy solid-state detectors since launch in mid 1995 and the fourth, the 90º proton telescope, had never worked. The current (as of December 31, 2004) noise level in the 30-80 keV channel of the 0º proton telescope on NOAA-14 is about 250-300 counts per second, a little bit lower than reported in January 2004. The detector noise does not affect the higher energy channels. The front solid-state detector in the 0º proton telescope has undoubtedly suffered radiation damage in launch, but the changes in effective energy thresholds is not known. The background count rate level in the >30 keV channel in the 0º electron telescope is about 70 counts per second (also somewhat lower than reported in January, 2004) while the >30 keV channel in the 90º electron telescope background count rate was about 7500 counts per second, 50% higher than reported in January, 2004. These levels, especially the 90º electron solid-state detector, are sufficiently high that conversion of sensor responses to electron fluxes in physical units will have errors, especially for low fluxes. During more intense events, when the sensor count rates are much higher than the noise background rates, the conversion to fluxes will have less error. The >100 keV electron energy channels in both the 0º and 90º telescopes are unaffected by the detector noise. The high background count rate observed in the 90º electron telescope may be largely due to an abnormally low electronic discrimination threshold for the >30 keV energy channel in that sensor. In-flight calibrations indicate that this threshold is (and has been since launch) at about 18.5 keV equivalent particle energy loss in the solid-state detector. In contrast, in-flight calibrations indicate that the electronic threshold of the 0º electron telescope channel is (and has been) about 24 keV equivalent energy loss. The historic in- flight calibration data for both the 0º and 90º electron telescopes have indicated solid- state detector noise levels of about 12 to 13 keV energy loss equivalent since launch in 1995. The last NOAA-14 calibration in December 2004 showed the 0º electron telescope noise level at 12.5 keV, the same as at the beginning of 2004. The detector noise level in the 90º detector had increased from about 13.5 keV at the beginning of 2004 to 14.5 keV at the end of 2004. These noise levels are higher than experienced in previous SEM-1 instruments (for example, 7-8 keV for the NOAA-12 solid-state electron telescopes). Both the 0º and 90º electron telescope, >300 keV channels suffered an electronic data multiplexer failure in 1999 and have not operated since. This problem appears to have first appeared on an intermittent basis in late1997 and continued intermittently through late-1998 before becoming permanently unusable in 1999. Use of the NOAA-14 >300 keV electron data after roughly November 1998 should be avoided. Of the MEPED solid-state detectors, only the three omni-directional detectors continue to operate entirely satisfactorily and those data are used in the web page 'Solar Proton' display. Users of these data should be aware that the P6 detector (>16 MeV protons) also responds to electrons of energies greater than several hundred keV. The response is caused by bremsstrahung produced in the Aluminum dome over the detector with the x- ray able to deposit enough energy in the solid-state detector to be detected. This response is particularly apparent in region south of the South Atlantic Anomaly. Beginning in mid 1995, about six-months after launch, the electron sensors in the TED on NOAA-14 began suffering a spurious count problem that was induced by encounters with intense auroral particle fluxes. This problem was never serious enough to declare the data non-usable but serious enough to compromise their value. The spurious count problem in the NOAA-14 TED instrument was mitigated in early 2001 by an increase in the electronic threshold discriminator levels. Since that time the TED instrument has provided satisfactory auroral electron data. The tabulation of those instances of a background response of more than 175 counts per readout period has remained less than 100 cases every 10-days throughout 2004. We believe that valid measurements of auroral particles over the energy range 300-20,000 eV continued to be made by the NOAA-14 TED until archiving was terminated, although the channeltron particle detectors have likely suffered a loss in gain over the years. SEM-2 (NOAA-15, NOAA-16, and NOAA-17) In the course of qualifying SEM-2 data at the end of 2004 an anomaly in the foot-of-the- magnetic-field-line (fofl) location was identified. This location (the point at which the magnetic field line threading the satellite is traced downward to intersect the atmosphere at 120 km altitude) is calculated by the archive program. This calculation involves an interpolation routine that uses the instantaneous sub-satellite geographic location together with a set of fofl geographic locations that have been pre-calculated each year for a grid of sub-satellite geographic latitude-longitude locations. In tracing the origin of this anomaly, an error was uncovered in the program that calculated the fofl locations for the grid array used in the interpolation. This error had existed since the inception of SEM-2 in 1998 and, thus, would have led to the similar anomalies in all the SEM-2 archive data. The error in creating the grid array leads, in turn, to an error in the geographic fofl locations (and associated dipole magnetic latitude, corrected magnetic latitude, and L- value) of up to several degrees. The fofl error appears in only one or two archive 32- second data frames (about 4 degrees latitude in satellite motion) adjacent to the satellite's crossing of the magnetic dip equator and, even then, only in certain geographic longitude ranges. Normally when the satellite approaches and crosses the magnetic dip equator, the latitude of fofl location changes slowly: about 0.1 degree or less every 8 seconds except for the discontinuous change when the satellite passes from one magnetic hemisphere to the other. This is because the satellite at those locations is moving roughly parallel to the magnetic field direction and along the same magnetic field line. The error in the calculation of the fofl location manifests itself as large changes in the calculated fofl latitude location (several tenths to several degrees) every 8-seconds at sub-satellite locations at and near the magnetic dip equator. The error in constructing the yearly array of fofl locations on the sub-satellite location grid was corrected. All SEM-2 archive data processed after January 3, 2005 will have correct fofl locations. We do not intend to reprocess the historical archive data. It should be emphasized that the fofl location errors are confined to sub-satellite locations within about 4 degrees of the magnetic dip equator and, even then, only in certain geographic longitude intervals. During 2004 there was also evidence uncovered that the P6 energy channels in the SEM-2 0º and 90º telescopes may have significant response to energetic (>500 keV) electrons in addition to the designed >6900 keV proton response. This is because the sweeping magnetic field in the proton telescope apertures is not effective in suppressing very energetic electrons from reaching the detector and very energetic electrons are capable of depositing >30 keV energy in the front solid-state detector and >60 keV in the back detector, thus triggering an event in the 0P6 or 90P6 channels. NOAA-15 The electron and proton solid-state detector telescopes on NOAA-15 continue to operate nominally. Detector noise and all electronic threshold levels remain the same since instrument turn-on in July 1998. There is clear evidence of radiation damage to the solid- state detectors in the 0º and 90º proton telescopes. The impact of this damage on the effective energy thresholds of these detectors is not well known. However, comparisons between proton telescope observations by NOAA-15 and by NOAA-16 that were made late in 2001 suggested at that time the nominal 30 keV energy threshold had increased to about 40 keV while the nominal 80 keV threshold had increased to about 100 keV. The change in effective energy thresholds has certainly become larger since late 2001 but no additional crosschecks have been conducted to quantify any further changes. The four omni-directional proton detectors also continue to operate nominally. The electronic thresholds remain at the same levels as at launch and there is no evidence of noise on the part of the solid-state detectors. Users of the data should be aware that because the electronic counting threshold on the P6 energy channel in the SEM-2 instrument is set to a much higher value than the case for SEM-1, the response to very energetic electrons is very much reduced in the SEM-2, P6 omni-directional detector. The TED in the SEM-2 on NOAA-15 continues to operate nominally. The electron gains on all channeltron detectors were checked for the in-flight calibration on November 30, 2004 and all are at satisfactory levels. NOAA-16 The electron and proton solid-state detector telescopes on NOAA-16 continue to operate nominally with the exception of radiation damage. Detector noise and all electronic threshold levels remain the same since instrument turn-on in September 2000. Comparisons between the responses of the 0º and 90º proton telescopes demonstrated that the effect of radiation damage to the front detectors in the proton telescopes on NOAA-16 became apparent during the latter 6-months of 2003. The degradation in solid-state detector performance, with corresponding increases in the proton energies required to register an event in the various energy bands, continued in 2004. The impact of the radiation damage on the effective proton energy thresholds in these telescopes has not been quantified. The four omni-directional proton detectors also continue to operate nominally. The electronic thresholds remain at the same levels as at launch and there is no evidence of noise on the part of the solid-state detectors. The TED in the SEM-2 on NOAA-16 continues to operate nominally. The electron gains on all channeltron detectors (both the electron and ion portions of the instrument) were checked at the end of 2002 and were found to be below specification. All the NOAA-16 channeltron bias voltages were increased on February 4, 2003 by two steps and the TED performance improved. The channeltron gains were checked again in November 2003 and the gain of the channeltron in the low-energy, 0º TED electron detector was found to be below specification. The channeltron bias voltage for the TED electron detector systems was increased by one step (to step 6 of 8) on December 2, 2003. Channeltron electron gains were again checked on December 1, 2004. The low-energy 0º TED electron channeltron detector continues to exhibit marginal gain. The low-energy 30º TED electron channeltron has very adequate gain. The channeltron gains in the high- energy 0º and 30º TED detectors are adequate although not as high as might be desired. The channeltron gains in the four TED proton detector systems are adequate. The channeltron bias level for the TED proton detectors on NOAA-16 remains at level 5 (of 8) and the bias levels for the TED electron detectors remains at level 6 (of 8.) The bias voltage continues to be inadequate for the 0º electron low-energy channeltron, but we are reluctant to increase the bias voltage still further. The contribution to the total integrated electron energy flux flowing into the atmosphere from the <1000 eV electrons is very modest. To increase the bias voltage further to compensate for the loss of sensitivity in that one detector would compromise the ability to handle future channeltron gain degradation in the more important >1000 keV TED electron detectors. NOAA-17 NOAA-17 was launched in June 2002 and the SEM-2 instrument was activated on July 19, 2002. The electron and proton solid-state detector telescopes on NOAA-17 are operating nominally. Detector noise levels and electronic threshold levels are well within specifications and are stable. The ratio of count rates between the 30-80 keV proton energy channels in the 0º and 90º proton telescopes during periods of significant proton fluxes are typically exceeding 1.0 in the NOAA-17 MEPED. A ratio greater than 1.0 is symptomatic of radiation damage to the sold-state detectors, especially the detector in the 90º telescope, which will have changed the proton energy threshold for detecting an event. The change in energy threshold is not quantified. The four omni-directional proton detectors are also operating nominally with electronic threshold levels well within specifications and stable. The TED in the SEM-2 on NOAA-17 is operating nominally. The electron gains on all channeltron detectors (both the electron and ion portions of the instrument) were checked on December 2, 2004 and were found at a satisfactory level. The channeltron bias voltages in the TED electron detectors are currently at level 3 (of 8) while the channeltron bias voltages in the TED proton detectors are currently at level 4 (of 8.) In summary, as of January 1, 2005 SEC is receiving and archiving data on a regular basis from the SEM packages of NOAA-15, NOAA-16, and NOAA-17. SEC has discontinued archiving NOAA-14 data as of January 1 although NOAA-14 data (and the rare NOAA- 12 data) will continue to be used in the real-time web displays of auroral activity and solar protons. Summary of SEM data recovery during 2004 NOAA-14 had the potential of making 10340 passes over the polar region during 2004. Of that potential, 9500 passes showed up in the data base (840 passes missing). This is a data recovery of 91.9%. Of the 9500 polar passes that were obtained, 9330 had sufficient data to estimate the hemispheric power input, a recovery rate of 98.2%. Both these percentages are somewhat lower than obtained in 2003 and reflect the fact that NOAA-14 is evolving towards a backup status. NOAA-15 had the potential of acquiring 10421 passes over the polar region during 2004. Of that potential, 10347 passes showed up in the data base (74 passes missing). This is a data recovery of 99.3%, marginally less than experienced in 2003. Of the 10347 polar passes that were obtained, 10316 had sufficient data to estimate the hemispheric power input, a recovery rate of 99.7% also marginally less than in 2003. The statistics for NOAA-16 data recovery during 2004 were satisfactory. Of the potential of acquiring 10331 polar passes during 2004, 10251 were logged into the data base. This is a recovery rate of 99.2%, again somewhat less than in 2004. Of the 10251 valid polar passes in the database, 10233 had sufficient data to estimate the hemispheric power input, a success rate of 99.8%. The statistics for NOAA-17 data recovery during 2004 are similar. Of the potential of acquiring 10415 polar passes during 2004, 10357 were logged into the data base. This is a recovery rate of 99.4%. Of the 10357 valid polar passes in the database, 10342 had sufficient data to estimate the hemispheric power input, a success rate of 99.8%. Interestingly, the bulk of the lost polar passes from NOAA-15, NOAA-16, and NOAA-17 (almost half of all during the year) occurred on February 7, 2004, for unknown reasons. cc Ron Zwickl Ernie Hildner Joe Kunches Rodney Viereck Howard Singer