Kitt Peak National Solar Observatory Research Articles

Nonaxisymmetric Component of the Solar Photospheric Magnetic Field

The longitudinal asymmetry of the photospheric magnetic field distribution is studied based on data from the Kitt Peak National Solar Observatory (synoptic maps for 1976–2016). Vector summation is used to weaken the effect of a stochastic component uniformly distributed along the longitude and to emphasize the stable nonaxisymmetric field component. Distributions of magnetic fields with different strength are considered: strong (B > 50 G), weak (B B > 5 G). It is shown that the longitudinal asymmetry in all the groups of fields varies in phase with the 11-year solar cycle. The asymmetry of the strong and medium fields varies in phase with the magnetic fluxes of these fields, whereas that of weak fields is in antiphase with the flux of the weak fields. The longitudinal distributions of the strong and medium magnetic fields resemble each other in shape: the distribution maximum is located at a longitude of ~180° during the ascent–maximum period of the solar cycle and at a longitude of ~0°/360° during the decrease–minimum period. Weak fields show the opposite picture: their distribution maximum is always located at the longitude of the strong and medium field minimum.

Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model

Aims. We study the properties of the coronal magnetic field according to the current sheet source surface (CSSS) model in 1976–2017 for all physically reasonable values of the three model parameters (cusp surface radius Rcs, source surface radius Rss, and current parameter a), and compare the CSSS field with the potential field source surface (PFSS) model field. Methods. We used the synoptic maps of the photospheric magnetic field from the Wilcox Solar Observatory (WSO), National Solar Observatory/Kitt Peak (NSO/KP), and the NSO Synoptic Optical Long-term Investigations of the Sun Vector Spectromagnetograph (SOLIS/VSM) in order to calculate the coronal magnetic field according to the CSSS and PFSS models. We calculated the coronal field strength, its latitudinal variation and neutral line location, as well as its polarity match with the heliospheric magnetic field. Results. The CSSS model can correct the erroneous latitudinal variation of the PFSS model if the source surface is sufficiently far out with respect to the cusp surface (Rss ≥ 3 ⋅ Rcs). The topology of the neutral line only slightly depends on source surface radius or current parameter, but excludes very low values of the cusp surface (Rcs ≤ 1.5). A comparison of the polarities gives an optimum cusp surface radius that varies in time between 2 and 5; a stronger current yields a larger optimum Rcs. Interestingly, the optimum polarity match percentages and optimum radii vary very similarly in the two models over the four solar cycles we studied. Conclusions. The CSSS model can produce a stronger total coronal flux than the PFSS model and correct its latitudinal variation. However, the topology of the CSSS model is rather independent of horizontal currents and remains very similar to that of the PFSS model. Therefore, the CSSS model cannot improve the match of field polarities between corona and heliosphere.

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles

We comparatively studied the long-term variation (1992-2017) in polar brightening observed with the Nobeyama Radioheliograph, the polar solar wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal hole distribution computed by potential field calculations of the solar corona using synoptic magnetogram data obtained at Kitt Peak National Solar Observatory. First, by comparing the solar wind velocity (V) and the brightness temperature (T_b) in the polar region, we found good correlation coefficients (CCs) between V and T_b in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V-T_b relationship as V =12.6 (T_b-10,667)^{1/2}+432. We also confirmed that the CC of V-T_b is higher than those of V-B and V-B/f, where B and f are the polar magnetic field strength and magnetic flux expansion rate, respectively. These results indicate that T_b is a more direct parameter than B or B/f for expressing solar wind velocity. Next, we analyzed the long-term variation of the polar brightening and its relation to the area of the polar coronal hole (A). As a result, we found that the polar brightening matches the probability distribution of the predicted coronal hole and that the CC between T_b and A is remarkably high, CC = 0.97. This result indicates that the polar brightening is strongly coupled to the size of the polar coronal hole. Therefore, the reasonable correlation of V-T_b is explained by V-A. In addition, by considering the anti-correlation between A and f found in a previous study, we suggest that the V-T_b relationship is another expression of the Wang-Sheeley relationship (V-1/f) in the polar regions.

Estimating Total Open Heliospheric Magnetic Flux

Over the solar-activity cycle, there are extended periods where significant discrepancies occur between the spacecraft-observed total (unsigned) open magnetic flux and that determined from coronal models. In this article, the total open heliospheric magnetic flux is computed using two different methods and then compared with results obtained from in-situ interplanetary magnetic-field observations. The first method uses two different types of photospheric magnetic-field maps as input to the Wang Sheeley Arge (WSA) model: i) traditional Carrington or diachronic maps, and ii) Air Force Data Assimilative Photospheric Flux Transport model synchronic maps. The second method uses observationally derived helium and extreme-ultraviolet coronal-hole maps overlaid on the same magnetic-field maps in order to compute total open magnetic flux. The diachronic and synchronic maps are both constructed using magnetograms from the same source, namely the National Solar Observatory Kitt Peak Vacuum Telescope and Vector Spectromagnetograph. The results of this work show that the total open flux obtained from observationally derived coronal holes agrees remarkably well with that derived from WSA, especially near solar minimum. This suggests that, on average, coronal models capture well the observed large-scale coronal-hole structure over most of the solar cycle. Both methods show considerable deviations from total open flux deduced from spacecraft data, especially near solar maximum, pointing to something other than poorly determined coronal-hole area specification as the source of these discrepancies.

Positive and Negative Photospheric Fields in Solar Cycles 21–24

Distribution of the positive and negative photospheric fields is studied on the base of synoptic maps of the photospheric magnetic field produced by the National Solar Observatory Kitt Peak (NSO Kitt Peak) for 1976-2016. In the analysis only the sign of the field irrespective of its strength is taken into account, emphasizing the role of the fields with average and weak strengths. Time changes in the positive and negative magnetic fields for two hemispheres, for the high latitudes and for the sunspot zone as well as their imbalances are considered. Distributions of fields of opposite polarities, which are defined mostly by the fields of the high latitudes, change with a 22-year cycle. The polarity imbalance in each hemisphere is closely connected with the dipole moment $g_{10}$. The imbalance of high latitudes for two hemispheres changes with the 22-year period and coincides with the sign of both the polar field in the southern hemisphere, and the quadrupole moment $g_{20}$. For the magnetic fields of the sunspot zone during ~75% of time a connection of the magnetic field imbalance with the quadrupole moment taken with the reversed sign $- g_{20}$ and with the sign of the polar field in the northern hemisphere is observed. The received results testify to cyclic changes in the polarity imbalance.

Line positions and intensities in the 7400–8600 cm−1 region of the ammonia spectrum

ABSTRACTThe positions and intensities of 1936 lines observed in the range 7400– of two absorption spectra of ammonia recorded at high resolution using Fourier transform spectroscopy are reported. The accuracy of these line positions is estimated to range from 0.001 to from the lower to the upper limits of the spectral range considered, while the accuracy of the line intensities is estimated to be around 10% or better. Also reported are less-accurately measured positions and intensities of 1985 lines retrieved from these two spectra or from only one of them. These results are compared with the data measured recently in a spectrum recorded in 1980 at the Kitt Peak National Solar Observatory [Barton et al., J. Mol. Spectrosc. 325, 7 (2016)] and provided in HITRAN 2016, as well as line positions and intensities measured in this work in the same Kitt Peak spectrum.

Analysis of the red and green optical absorption spectrum of gas phase ammonia

Room temperature NH3 absorption spectra recorded at the Kitt Peak National Solar Observatory in 1980 are analyzed. The spectra cover two regions in the visible: 15,200 – 15,700 cm−1 and 17,950 – 18,250 cm−1. These high overtone rotation-vibration spectra are analyzed using both combination differences and variational line lists. Two variational line lists were computed using the TROVE nuclear motion program: one is based on an ab initio potential energy surface (PES) while the other used a semi-empirical PES. Ab initio dipole moment surfaces are used in both cases. 95 energy levels with J=1−7 are determined from analysis of the experimental spectrum in the 5νNH (red) region and 46 for 6νNH (green) region. These levels span four vibrational bands in each of the two regions, associated with stretching overtones.

Latitudinal Profiles of the Photospheric Magnetic Field in Solar Cycles 19–21

For groups of photospheric magnetic fields differing in strength the time averaged synoptic maps were obtained on the basis of the National Solar Observatory Kitt Peak data (1976-2003). The latitudinal profiles of magnetic field fluxes were considered separately for each 5 G interval of the field strength B. The changes both of the profile maxima and of the latitudinal localization of these maxima were studied. The obtained results show that the latitudinal distribution of magnetic fields considerably changes at certain values of the field strength: 5 G, 15 G, and 50 G. The magnetic flux for field groups differing in strength, monotonically decreases with increase of strength for all fields with strength B>5 G. For these fields the fluxes of the southern hemisphere exceed fluxes of the northern hemisphere. A very special group is represented by the weakest fields B<5 G, which are in antiphase both in localization and in time changes with stronger fields.

Latitudinal Distribution of Photospheric Magnetic Fields of Different Magnitudes

Photospheric magnetic fields are studied using synoptic maps from 1976 to 2003 produced at the National Solar Observatory, Kitt Peak (NSO/KP). Synoptic maps were averaged over the time interval of nearly three solar cycles (Solar Cycles 21 – 23). The change in the latitudinal distribution was considered for the following groups of magnetic field values: $B = 0 \,\mbox{--}\, 5~\mbox{G}$ , $B = 5 \,\mbox{--}\, 15~\mbox{G}$ , $B = 15 \,\mbox{--}\, 50~\mbox{G}$ , and $B > 50~\mbox{G}$ . Magnetic fields in each of the above groups have common latitudinal distribution features, while for different field groups these features are significantly different. Each of the groups is closely related to a certain manifestation of solar activity. Strong magnetic fields are connected with two types of solar activity: active regions (magnetic fields $B>15~\mbox{G}$ ) that are related to sunspot zones, and polar faculae (magnetic fields $50~\mbox{G} > B > 15~\mbox{G}$ ) that occupy latitudes around $65^{\circ}-75^{\circ}$ . Fields from 5 to 15 G occupy the polar regions and are connected with polar coronal holes (the global solar dipole). Fields of $B<5~\mbox{G}$ occupy a) the equatorial region and b) latitudes $40^{\circ}$ – $60^{\circ}$ .

Properties of the magnetic fields of coronal holes with active regions

We determine the structure of the magnetic fields of coronal holes (CHs) and investigate its change in connection with the emergence of active regions (ARs) in CHs. Based on our observations in the HeI 1083 nm line performed with the CrAO TST-2 telescope, we have selected CHs of two types: without (15 CHs) and with (28 CHs) ARs. Magnetograms obtained at the Kitt Peak National Solar Observatory have been used to calculate the magnetic fields of the same objects.

Solar magnetic cycle: Peculiarities of the photospheric field distribution

Synoptic maps for 1976–2003 obtained at the Kitt Peak National Solar Observatory are used to analyze the longitudinal distribution of the solar photospheric magnetic field. The superposition of synoptic maps gives different pictures for the rise-maximum phase and the decline-minimum phase. Two characteristic periods correspond to different situations in the 22-year solar magnetic cycle in the course of which both the global magnetic field and the magnetic field of the leading sunspot in a group change their sign.

코로나 홀을 이용한 CIR과 지자기 폭풍의 경험적 예보 연구

이 연구에서 우리는 코로나 홀(Coronal hole, CH)의 정보(위치, 면적)를 이용하여 CIR(Corotating Interaction Regions)과 지자기폭퐁(Geomagnetic Storm)에 대한 경험적인 예보를 수행하였다. 이것을 위해 1996년 1월 <TEX>$\sim$</TEX> 2003년 11월까지의 미국 국립 천문대-Kitt Peak 관측소의 He I <TEX>$1083{\AA}$</TEX> 영상으로부터 코로나 홀 자료를 얻고, Choi et al.(2009)로부터 확인된 CIR과 지자기폭풍 자료를 활용하였다. 지자기 폭풍을 일으키는 코로나 홀의 특성을 고려하여 코로나 홀의 중심이 <TEX>$N40^{\circ}$</TEX>와 <TEX>$S40^{\circ}$</TEX> 사이, <TEX>$E40^{\circ}$</TEX>와 <TEX>$W20^{\circ}$</TEX> 사이에 위치하고 태양 반구에 대한 면적 비율이 다음과 같은 세 가지 경우를 선택하였다: (1) case 1: 0.36% 이상, (2) case 2: 0.66% 이상, (3) case 3: <TEX>$1996{\sim}2000$</TEX>년 동안에는 0.36%, <TEX>$2001{\sim}2003$</TEX>년 동안에는 0.66% 이상. 우리는 각 경우에 대하여 예보의 성공 유무를 확인할 수 있는 예보 분할표(Contingency Table)를 만들고, 그들의 태양 주기 위상(Solar cycle phase)에 대한 의존성을 조사하였다 분할표로부터 우리는 PODy(the probability of detection yes), FAR(the false alarm ratio), Bias(the ratio of "yes" predictions to "yes" observations) 그리고 CSI(critical success index)와 같은 예보 평가 지수를 결정하였다. 이와 같은 예보에서 PODy와 CSI가 상대적으로 더 중요한 사실을 고려하여, 우리는 가장 좋은 후보가 case 3이라는 것을 발견하였다. 이 경우에 두 가지 예보에 대한 예보평가 지수는 아래와 같다: CH-CIR의 경우는 PODy=0.77, FAR=0.66, Bias=2.28, CSI=0.30이고, CH-storm의 경우는 PODy=0.81, FAR=0.84, Bias=5.00, CSI=0.16이다. 또한 태양 활동 극대기 이후 감쇄기간 동안의 지수들이 태양 극대기 이전의 값들 보다 훨씬 잘 예보되고 있음을 알 수 있다. 따라서 코로나 홀을 이용한 CIR의 예보는 충분한 가능성을 보여주고 있으나, 지자기 폭풍의 예보는 너무 많은 허위 예보로 인하여 다소 어려울 것으로 비상된다. In this study, we suggest an empirical forecast of CIR (Corotating Interaction Regions) and geomagnetic storm based on the information of coronal holes (CH). For this we used CH data obtained from He I <TEX>$10830{\AA}$</TEX> maps at National Solar Observatory-Kitt Peak from January 1996 to November 2003 and the CIR and storm data that Choi et al. (2009) identified. Considering the relationship among coronal holes, CIRs, and geomagnetic storms (Choi et al. 2009), we propose the criteria for geoeffective coronal holes; the center of CH is located between <TEX>$N40^{\circ}$</TEX> and <TEX>$S40^{\circ}$</TEX> and between <TEX>$E40^{\circ}$</TEX> and <TEX>$W20^{\circ}$</TEX>, and its area in percentage of solar hemispheric area is larger than the following areas: (1) case 1: 0.36%, (2) case 2: 0.66%, (3) case 3: 0.36% for 1996-2000, and 0.66% for 2001-2003. Then we present contingency tables between prediction and observation for three cases and their dependence on solar cycle phase. From the contingency tables, we determined several statistical parameters for forecast evaluation such as PODy (the probability of detection yes), FAR (the false alarm ratio), Bias (the ratio of "yes" predictions to "yes" observations) and CSI (critical success index). Considering the importance of PODy and CSI, we found that the best criterion is case 3; CH-CIR: PODy=0.77, FAR=0.66, Bias=2.28, CSI=0.30. CH-storm: PODy=0.81, FAR=0.84, Bias=5.00, CSI=0.16. It is also found that the parameters after the solar maximum are much better than those before the solar maximum. Our results show that the forecasting of CIR based on coronal hole information is meaningful but the forecast of goemagnetic storm is challenging.

Reconstruction of solar UV irradiance since 1974

Variations of the solar UV irradiance are an important driver of chemical and physical processes in the Earth's upper atmosphere and may also influence global climate. Here we reconstruct solar UV irradiance in the range 115–400 nm over the period 1974–2007 by making use of the recently developed empirical extension of the Spectral And Total Irradiance Reconstruction (SATIRE) models employing Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) data. The evolution of the solar photospheric magnetic flux, which is a central input to the model, is described by the magnetograms and continuum images recorded at the Kitt Peak National Solar Observatory between 1974 and 2003 and by the Michelson Doppler Imager instrument on SOHO since 1996. The reconstruction extends the available observational record by 1.5 solar cycles. The reconstructed Ly‐α irradiance agrees well with the composite time series by Woods et al. (2000). The amplitude of the irradiance variations grows with decreasing wavelength and in the wavelength regions of special interest for studies of the Earth's climate (Ly‐α and oxygen absorption continuum and bands between 130 and 350 nm) is 1–2 orders of magnitude stronger than in the visible or if integrated over all wavelengths (total solar irradiance).

Statistical Analysis of the Relationships among Coronal Holes, Corotating Interaction Regions, and Geomagnetic Storms

We have examined the relationships among coronal holes (CHs), corotating interaction regions (CIRs), and geomagnetic storms in the period 1996 – 2003. We have identified 123 CIRs with forward and reverse shock or wave features in ACE and Wind data and have linked them to coronal holes shown in National Solar Observatory/Kitt Peak (NSO/KP) daily He i 10 830 A maps considering the Sun – Earth transit time of the solar wind with the observed wind speed. A sample of 107 CH – CIR pairs is thus identified. We have examined the magnetic polarity, location, and area of the CHs as well as their association with geomagnetic storms (Dst≤−50 nT). For all pairs, the magnetic polarity of the CHs is found to be consistent with the sunward (or earthward) direction of the interplanetary magnetic fields (IMFs), which confirms the linkage between the CHs and the CIRs in the sample. Our statistical analysis shows that (1) the mean longitude of the center of CHs is about 8°E, (2) 74% of the CHs are located between 30°S and 30°N (i.e., mostly in the equatorial regions), (3) 46% of the CIRs are associated with geomagnetic storms, (4) the area of geoeffective coronal holes is found to be larger than 0.12% of the solar hemisphere area, and (5) the maximum convective electric field E y in the solar wind is much more highly correlated with the Dst index than any other solar or interplanetary parameter. In addition, we found that there is also a semiannual variation of CIR-associated geomagnetic storms and discovered new tendencies as follows: For negative-polarity coronal holes, the percentage (59%; 16 out of 27 events) of CIRs associated with geomagnetic storms in the first half of the year is much larger than that (25%; 6 out of 24 events) in the second half of the year and the occurrence percentage (63%; 15 out of 24 events) of CIR-associated storms in the southern hemisphere is significantly larger than that (26%; 7 out of 27 events) in the northern hemisphere. Positive-polarity coronal holes exhibit an opposite tendency.

Solar Cycle Changes in Sunspot Umbral Intensity

The minimum intensities of sunspot umbrae were measured from 1992 through 2003 using the National Solar Observatory Kitt Peak Vacuum Telescope spectromagnetograph data. The resulting 3931 umbral measurements reveal a solar cycle variation in the umbral intensity, with umbrae appearing brighter on average at cycle minimum and darker at cycle maximum. Recent studies of umbral intensity have been in direct conflict with each other, showing decreasing, increasing, or no umbral intensity trends. By providing a longer temporal baseline, our new measurements uncover a solar cycle oscillation in umbral intensity. From this new perspective we show how previous studies agree with our work and with each other when the same phase of the solar cycle is examined. Also in agreement with other investigators, the solar cycle variation in the daily average umbral area, the lognormal distribution of umbral area, and the near constancy of the mean umbral radius during the solar cycle are seen in this data.

Correlation Height of the Source Region of Si II Emission Lines in Coronal Hole Regions

The height of the source region of Si II emission lines characterizes the height of the bottom layer of solar atmosphere's transition region. The correlation analysis of the intensities of ultraviolet spectral lines and the threedimensional structure of magnetic field yielded by force-free extrapolation is a new method for determining the height of ultraviolet emission lines’ source region. It has been found that the height thus obtained is larger than that given by traditional viewpoint. Because the existing numerical analyses with this method are scarce, this result has to be further verified with more observational materials. In this work, this method is applied to the Si II emission lines observed by SOHO/SUMER for the solar surface region beneath the solar coronal hole at southern pole and to the magnetic fields measured by National Solar Observatory/Kitt Peak (NSO/KP) in U.S.A. The correlation height of the source region of Si II emission lines in coronal hole region is approximately 5.0 Mm. This result supports the conclusion that the height of the bottom layer of transition region in coronal hole region is larger than that in quiet regions. Moreover, some new phenomena have been discovered and their causes are probed.

Relation between solar wind velocity and properties of its source region

Abstract Different kinds of coronal holes are sources of different kind of solar winds. A successful solar wind acceleration model should be able to explain all those solar winds. For the modeling it is important to find a universal relation between the solar wind physical parameters, such as velocity, and coronal physical parameters such as magnetic field energy. To clarify the physical parameters which control the solar wind velocity, we have studied the relation between solar wind velocity and properties of its source region such as photospheric/coronal magnetic field and the size of each coronal hole during the solar minimum. The solar wind velocity structures were derived by using interplanetary scintillation tomography obtained at Solar-Terrestrial Environment Laboratory, Japan. Potential magnetic fields were calculated to identify the source region of the solar wind. HeI 1083 nm absorption line maps obtained at Kitt Peak National Solar Observatory were used to identify coronal holes. As a result, we found a relation during solar minimum between the solar wind velocity and the coronal magnetic condition which is applicable to different kind of solar winds from different kind of coronal holes.

Coronal plasma flows and magnetic fields in solar active regions

During the early days of the SOHO mission, SUMER observed a few active regions (ARs) connected with sunspots on the Sun and took their images and spectra in various EUV emission lines. In addition to these spectroscopic data magne- tograms of the photospheric footpoint regions of the AR loops were available from the MDI on SOHO and the National Solar Observatory/Kitt Peak (NSO/KP), data which here are used to construct the coronal magnetic field of the ARs by force-free- field extrapolation. The combined data set is analysed with respect to the large-scale circulation of coronal matter, which means that the Dopplershifts of various lines used as tracers of the plasma flow are investigated in close connection with the ambient magnetic field, which is found to be either closed or open in the coronal volume considered. The Dopplershift pattern is found to be clearly linked with the field topology, and several regions of strong velocity shear are identified. We also estimate the coronal currents. We discuss the results of this mainly phenomenological correlative study with the perspective to understand coronal heating and mass supply to the extended corona, and with respect to the role played by the field in guiding and constraining plasma flows.

Near infrared spectroscopy of carbon dioxide. II: 16O 13C 16O and 16O 13C 18O line positions

High-resolution near-infrared (4000–8500 cm −1) spectra of 13C-enriched carbon dioxide have been recorded using the McMath-Pierce Fourier transform spectrometer at the Kitt Peak National Solar Observatory. We observed over 1000 line positions for the 16O 13C 16O isotopologue, the majority of which have previously been observed only in spectra of the Venusian atmosphere [J. Mol. Spectrosc. 67 (1977) 304]. These have been analyzed to determine spectroscopic constants for 28 different vibrational states. The analysis yielded RMS fitting residuals <1.5 × 10 −4 cm −1 for the strongest bands and RMS residuals <5 × 10 −4 cm −1 for most other fitted bands. A 5% 18O-enrichment in the sample enabled us to observe 410 line positions from 5 near-infrared vibrational bands of the 16O 13C 18O isotopologue. Analysis of the 16O 13C 18O bands yielded RMS fitting residuals <2 × 10 −4 cm −1. Additionally, the first fits for the 16O 13C 18O 11101 ← 01101 and 11102 ← 01101 hot bands yielded RMS residuals of 2.3 × 10 −4 and 2.2 × 10 −4 cm −1, respectively. Critical reevaluations of the spectroscopic constants for the low lying vibrational states for both isotopologues have been performed as part of the analysis.

Statistical Properties of Superpenumbral Whorls around Sunspots

We study properties of 897 superpenumbral fibrils using Hα Big Bear Solar Observatory (BBSO) and photospheric magnetic field National Solar Observatory/Kitt Peak (NSO/KP) data of 139 sunspots between 2000 July and 2001 April. From this low-resolution data, we find that about one-third of all superpenumbral fibrils begin inside the penumbra. The typical length of fibrils is 2.7 times the sunspot white-light penumbral radius. A majority of the fibrils are curved, i.e., 67% of them exhibit bow-extent/footpoint separation greater than 0.1. Both clockwise and counterclockwise fibrils are typically present within the same superpenumbra. We show that the topology of fibrils is clearly affected by distribution of magnetic fields around the sunspot.