Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory

Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error

The smallest observable elements of magnetic flux

We have followed disappearing elements of magnetic flux to determine the smallest elements detectable with the Big Bear videomagnetograph. All the elements followed were disappearing through interaction with elements of opposite polarity. The last remaining visible segment of magnectic field of such features can be used to infer the total magnetic flux of these and other small flux elements visible on the magnetograms. We used both photographic and digital videomagnetograms combining 4096 Zeeman frames made at Big Bear. Fifteen elements were measured near the vanishing point, in a 2–8 hr period. The minimum observable fluxes fall in the range of 1.0 × 10¹⁶ to 1.4 × 10¹⁷ Mx, and the apparent size of these elements is in the range of 1 to 9 square arc sec. The process of disappearance appears to be a smooth one. The smallest detectable elements of network field and ephemeral regions (ER) appear to be the same as the small intra-network (IN) field elements. The present limit is still instrumental; elements smaller than 1 × 10¹⁶ would not have been detected

Complexity of emerging magnetic flux during lifetime of solar ephemeral regions

As a relatively active region, ephemeral region (ER) exhibits highly complex pattern of magnetic flux emergence. We aim to study detailed secondary flux emergences (SFEs) which we define as bipoles that they appear close to ERs and finally coalesce with ERs after a period. We study the SFEs during the whole process from emergence to decay of 5 ERs observed by the Helioseismic and Magnetic Imager (HMI) aboard Solar Dynamics Observatory (SDO) . The maximum unsigned magnetic flux for each ER is around $10^{20}$ Mx. Each ER has tens of SFEs with an average emerging magnetic flux of approximately 5$\times10^{18}$ Mx. The frequency of normalized magnetic flux for all the SFEs follows a power law distribution with an index of -2.08 . The majority of SFEs occur between the positive and negative polarities of ER , and their growth time is concentrated within one hour. The magnetic axis of SFE is found to exhibit a random distribution in the 5 ERs. We suggest that the relationship between SFEs and ERs can be understood by regarding the photospheric magnetic field observations as cross-sections of an emerging magnetic structure. Tracking the ERs' evolution, we propose that these SFEs in ERs may be sequent emergences from the bundle of flux tube of ERs, and that SFEs are partially emerged $\Omega$-loops.Comment: 12 pages, 9 figures, 1 table and accepted for publication in the Astrophysical Journa

Flux distribution of solar intranetwork magnetic fields

Big Bear deep magnetograms of June 4, 1992 provide unprecedented observations for direct measurements of solar intranetwork (IN) magnetic fields. More than 2500 individual IN elements and 500 network elements are identified and their magnetic flux measured in a quiet region of 300 × 235 arc sec. The analysis reveals the following results: 1. (1) IN element flux ranges from 10¹⁶ Mx (detection limit) to 2 × 10¹⁸ Mx, with a peak flux distribution of 6 × 10¹⁶ Mx. 2. (2) More than 20% of the total flux in this quiet region is in the form of IN elements at any given time. 3. (3) Most IN elements appear as a cluster of mixed polarities from an emergence center (or centers) somewhere within the network interior. 4. (4) The IN flux is smaller than the network flux by more than an order of magnitude. It has a uniform spatial distribution with equal amount of both polarities. It is speculated that IN fields are intrinsically different from network fields and may be generated from a different source as well

Magnetic Evolution and Temperature Variation in a Coronal Hole

We have explored the magnetic flux evolution and temperature variation in a coronal-hole region, using Big Bear Solar Observatory (BBSO) deep magnetograms and {\it SOHO}/EIT images observed from 2005 October 10 to 14. For comparison, we also investigated a neighboring quiet region of the Sun. The coronal hole evolved from its mature stage to its disappearance during the observing period. We have obtained the following results: (1) When the coronal hole was well developed on October 10, about 60 % of the magnetic flux was positive. The EUV brightness was 420 counts pixel$^{-1}$, and the coronal temperature, estimated from the line ratio of the EIT 195 {\AA} and 171 {\AA} images, was 1.07 MK. (2) On October 14, when the coronal hole had almost disappeared, 51 % of the magnetic flux was positive, the EUV radiance was 530 counts pixel$^{-1}$, and the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an irregular variation, with a mean value of 870 counts pixel$^{-1}$. The temperature was almost constant at 1.11 MK during the five-day observation. Our results demonstrate that in a coronal hole less imbalance of the magnetic flux in opposite polarities leads to stronger EUV brightness and higher coronal temperatures

Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory

Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error