German physicist, Martin Brendel 1862-1939

1. Feasibility Preliminary Experiments Abstract Since 1892 when aurora was first imaged by Martin Brendel, useful auroral images have been obtained only when the aurora is in darkness. While UV imagers onboard satellite provide global auroral dynamics, the sunlit aurora in the UV band is overwhelmed by the UV airglow that has the same wavelengths with the UV auroral emissions. The visible band imaging is feasible only when the aurora is in darkness to avoid the sunlight contamination. However, sunlit aurora (such as dayside aurora) is closely related to the solar wind – magnetosphere – ionosphere coupling. In addition, limited land area has badly restricted the capability of imaging dayside aurora from the northern hemisphere and nightside aurora from the southern hemisphere. We have confirmed that sunlit aurora can be imaged using a near-infrared (NIR) camera on board the balloon platform flying in Antarctica or Arctic. This method provides a unique capability for dayside and conjugate auroral investigations. The new method is also cost effective comparing to space-borne imagers, and offers capabilities not obtainable from space and the ground. With the accomplishment of identifying auroral dynamics in sunlight and darkness, in the south and north simultaneously, our knowledge and understanding of auroral phenomenon and its causes will be expanded. From the ground at Poker Flat, using the JPL NIR camera and a narrow field-of-view lens (7.5°) have yielded promising results. Images were obtained without any filter yet aurora could still be separated out of the bright background sky (that is mainly the OH airglow in 1450-1650 nm) during twilight with a solar depression angles of about 6°, which corresponds to the sky intensity at 35-40 km altitude during the Antarctic summer. MODTRAN model predictions indicate that sky brightness (Rayleigh scattered sunlight) and atmospheric absorption favor the near infrared (NIR) for daytime observations (Zhou et al., GRL2007). Imaging Sunlit Aurora from BalloonDirk Lummerzheim1, Xiaoyan Zhou2, 1Geophysical Institute, University of Alaska, Fairbanks, Fairbanks, AK, United States2UCLA/IGPP (on leave from JPL) background sky brightness removed Bright auroral features in that wavelength region are: raw image 0617:07 UT April 13, 2005 Images at 1 sec intervals, 7.5° FOV, 30° above the northern horizon, sun at 6° depression 0616:23-0616:33 UT April 13, 2005 (Zhou et al., GRL, 2007) Possible Applications Motivation Dayside Aurora: high spatial resolution images of interplanetary shock/pressure impulse induced aurora gives clues about the acceleration mechanism, e.g. well defined discrete arcs originate from other mechanisms than diffuse patches (Zhou et al., JGR2003). Aurora borealis is one of the oldest and well known space physics phenomena and is the most visible characteristic of the high latitude ionosphere, the magnetospheric dynamics as well as the solar wind-magnetosphere-ionosphere coupling and interaction. 1667 nm 1429 nm 1250 nm 1111 nm 1000 nm 2000 nm A closer view of N2+Meinel 0-0 band emission German physicist,Martin Brendel 1862-1939 1136 nm 1124 nm 1111 nm 1099 nm 1087 nm Zhou et al., GRL, 2007 Remick et al., JASTP, 2001 Conjugate Aurora The relative auroral brightness (i.e., auroral intensity/sky intensity) is shown in Figure (b), which is obtained for an assumed auroral energy flux of 10 mW/m2, representing moderate auroral brightness during the brightest Antarctic summer sky (with LAZ=90°). For each vertical segment, the top mark corresponds to the intensity ratio at 50 km altitude, the bottom to the intensity ratio at 40 km altitude. For the N2+ Meinel line at 1109 nm, the ratio increases from 0.15 to 0.75 as the altitude increases from 40 to 50 km. It should be noted that in general when the auroral signal over background ratio is 0.1 or higher, the aurora is detectable. • The first successful auroral photograph that was taken by Martin Brendelon 1 February 1892 in Alten Fiord, Lapland and was published in the Century Magazine on October 1897. Conjugate aurora imaging can be obtained: balloon borne daylight auroral imaging on the southern (summer) hemisphere simultaneously complemented by existing ground-based ASI observations on the northern (winter) hemisphere. Technology • In the past 120 years, auroras have only been imaged when they are in darkness. However, compelling scientific questions can be addressed when sunlit auroras (or auroras under sunlight) can be imaged. Such questions include • How does the dayside aurora respond to solar wind transient variations? • Are auroras hemispherically symmetric? • Are auroral forms and their variations under sunlight the same as those in darkness? Conclusions An existing JPL built high performance Focal Plane Array (FPA) hybrid InGaAs camera has the needed wavelength sensitivity at room temperature. Balloon flights to 49 km altitude with 700 kg payload have been made by NASA. The new method is cost effective comparing to space-borne imagers, and offers capabilities not obtainable from space and the ground. With the accomplishment of identifying auroral dynamics in sunlight and darkness, in the south and north simultaneously, our knowledge and understanding of auroral phenomenon and its causes will be expanded, all the science questions mentioned above can be addressed in near future based on balloon observations. Zhou et al., GRL, 2007