Visible and Near-Infrared Contrast of Faculae in Active Region NOAA 8518

We compare the contrast of faculae, in visible light and in the near infrared (NIR), that were associated with the active region NOAA 8518 which crossed the solar disk from April 19 to 27, 1999. We obtained NIR continuum images at 1.6 μm at the Big Bear Solar Observatory (BBSO) with an Indium Gallium Arsenide (In Ga As) NIR digital camera. We also obtained high-resolution longitudinal magnetograms and visible light filtergrams at 610.3 nm with the newly developed Digital Vector Magnetograph (DVMG). Our data show that the contrast of faculae has the same sign in both the visible and the NIR. We did not find any so-called ``dark faculae', faculae that are bright in the visible and simultaneously dark in the NIR. We determined a threshold magnetic flux density that separates pores from faculae.

How much has the Sun influenced Northern Hemisphere temperature trends?An ongoing debate

In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature.Half of these estimates are"low variability"and half are"high variability".Meanwhile,five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using:1)only rural weather stations;2)all available stations whether urban or rural(the standard approach);3)only sea surface temperatures;4)tree-ring widths as temperature proxies;5)glacier length records as temperature proxies.The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates,suggesting that urbanization bias might still be a problem in current global temperature datasets-despite the conclusions of some earlier studies.Nonetheless,all five estimates confirm that it is currently warmer than the late 19th century,i.e.,there has been some"global warming"since the 19th century.For each of the five estimates of Northern Hemisphere temperatures,the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting.The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended"anthropogenic forcings"time series.For all five Northern Hemisphere temperature series,different TSI estimates suggest everything from no role for the Sun in recent decades(implying that recent global warming is mostly human-caused)to most of the recent global warming being due to changes in solar activity(that is,that recent global warming is mostly natural).It appears that previous studies(including the most recent IPCC reports)which had prematurely concluded the former,had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates.Therefore,several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.

Length Scale of Photospheric Granules in Solar Active Regions

Investigating the length scales of granules could help understand the dynamics of granules in the photosphere.In this work,we detected and identified granules in an active region near disk center observed at wavelength of TiO(7057?)by the 1.6 m Goode Solar Telescope(GST).By a detailed analysis of the size distribution and flatness of granules,we found a critical size that divides the granules in motions into two regimes:convection and turbulence.The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate“flat”in flatness,which reveal that these granules are dominated by convection.Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness,which indicate that the small granules are dominated by turbulence.Hence,for the granules in active regions,they are originally convective in large length scale,and directly become turbulent once their sizes turn to small,likely below the critical size of 600 km.Comparing with the granules in quiet regions,they evolve with the absence of the mixing motions of convection and turbulence.Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions.The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules.Such walls cause convective granules extending to smaller sizes on one hand,and cause wide intergranular lanes on the other hand.The small granules isolated in such wide intergranular lanes are continually sheared,rotated by strong downflows in surroundings and hereby become turbulent.