Science Accomplishments from Polar FUV Imaging

Ching-I Meng, Patrick T. Newell, Kan Liou, James F. Carbary, and Jih-Hong Shue

The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland

(A full publication list and reprints)

1.      The Source of the 1500 Auroral Hot Spot

·        Liou et al. [1999] showed that the most intense afternoon auroral activity maps to the nightside plasma sheet.

2.      The Suppression of Aurora by Sunlight

·        Liou et al. [1997] and Shue et al. [2001a] showed that intense aurora are suppressed by sunlight.

3.      The Solar Cycle Effect on Aurora

·        Shue et al. [2001a] showed that there are fewer auroras under sunlit conditions when the F10.7 number is higher.  This strongly implies a solar cycle effect different from that commonly supposed.

4.      An Auroral Signature Decoded: Bursty Bulk Flows

·        Sergeev et al. [1999] showed that auroral streamers observed by Polar UVI correspond to bursty bulk flows as observed by Geotail ([as did Fairfield et al., 1999]).

5.      Substorm Onset Timing

·        Liou et al. [1999, 2000a, 2000b, 2001c, 2002a] made substantial progress in establishing a consistent substorm sequence around t=0, placing various common onset identifiers in their proper order.

6.      Quantified Auroral Power Response to Solar Wind Input and Substorm Onset

·        Liou et al. [1998] quantified the auroral power response to solar wind input, including finding the best response function.

·        Newell et al. [2001a] determined the quantitative relationship between auroral power, polar cap size, and magnetotail stretching.

·        Newell et al. [2001b] quantified auroral power response to substorm onset; for example determining that nightside power averages 62% higher following onset.

7.      The Asymmetric Response of Day-night Aurora to Sunlight

·        Meng et al. [2001] and Liou et al. [2001a] showed that dayside auroras are enhanced under sunlit conditions, in contrast to nightside auroras, which are suppressed under sunlit conditions.

8.      Dependence of Global Auroral Patterns on Interplanetary Magnetic Field

·        Shue et al. [2001b, 2001c, 2002b] produced global auroral patterns in terms of the X, Y, and Z components of the interplanetary magnetic field (IMF).  These patterns show that the aurora reaches the highest activity when all the components of the IMF are negative.

9.      Discovery of midday sub-auroral patches (MSPs)

·        Liou et al. [2002b] reported a new category of dayside auroral transients using Polar UVI images. The transisents were found to occur concurrently with storm sudden commencements in response to the compression of the magnetosphere by interplanetary shocks.

10.      The convection aurora

·        Shue et al. [2002b] described the global morphology of the convection aurora, contrasting the substorm aurora.

11.      Superposed Epoch Analysis of Substorm Power

·        Polar UVI was used to study the time history of auroral power for 390 substorms, using superposed epoch analysis [Newell et al., 2001]. In the premidnight sector, for example, auroral power actually dropped by about 10% prior to substorm onset, but after onset more than tripled, with most of the increase occuring within the first 3 minutes. Subsequent decay of auroral power was far slower, taking approximately 2 hours. Dayside auroral power was found to be invariant with respect to substorm onset.

12.      Seasonal and Diurnal Variations of Polar Cap Size

·        The seasonal and diurnal variations in the magnetospheric have previously been investigated using ground-based magnetometer chains (where the response depends directly on local conductivity). Newell et al. [2002] used Polar UVI to get the first spacecraft-based determination of seasonal and diurnal activity. The equinoctial preference was confirmed (the polar cap is largest around equinox). The details of the universal time variation suggest that ionospheric conductivity can account for the equinoctial effect, since the polar cap is largest when the nightside oval of both hemispheres is in darkness.

13.      Relationship between plasma sheet fast flows and nightside auroral precipitation

·        Shue et al. [2003], using Geotail and Polar data, reported that the rate of nightside auroral power change is independent of the earthward plasma sheet fast flow, indicating that the plasma fast flows are not necessarily associated with large-scale auroral activity.

14.      Do interplanetary shocks trigger substorms?

·        Liou et al. [2003, 2004] reported that interplanetary shocks might trigger auroral electrojets enhancements (compression bays) but not auroral breakups. They also show that compression bays are associated with a direct-driven instead of loading-unloading process.

15.      Storm-substorm relationship

·        Wu et al. [2004] studied 23 storms and 167 concurrent substorms and found that substorms occur more frequently in the main phase (60%) than in the recovery phase (40%) of storms. However, there is no clear indication that the occurrence of substorm affects the storm intensity.

16.      A new Kp-based auroral boundary model

·        A simple model of the auroral boundaries is constructed by binning several months' of Polar UVI images by Kp index. The peak locations and peak intensities are found in the indexed images. The boundary and peak locations vary linearly with Kp index, and the coefficients of the linear fits are tabulated for each MLT. As a general rule of thumb, the UV intensity peak shifts 1 degree in magnetic latitude for each increment in Kp. The statistical model allows calculation of the auroral boundaries at most MLTs as a function of Kp and can serve as an approximation to the shape and extent of the statistical oval.

17.      Ionospheric plasma flows on the theta aurora

·        Based on two-dimensional SuperDARN radar measurements, Liou et al. [2005a] reported that the plasma flow on the nightside part of theta auroras is antisunward, which contradicts previous in situ measurements (mostly dayside or/and very high latitude) in which plasma flow is sunward.

18.      Neutral composition changes as a major cause of negative ionospheric storms

·        Liou et al. [2005b] demonstrated for the first time that regions of a reduced column O/N2 ratio seen at dayside in both hemispheres coincide well with regions of depleted ionospheric plasma during storm times.

References

Carbary, J. F., A Kp-based model of auroral boundaries, Space Weather., in press, 2005.

Liou, K., P. T. Newell, C.-I Meng, M. Brittnacher, and G. Parks, Synoptic auroral distribution:  A survey using Polar ultraviolet imagery, J. Geophys. Res., 102, 27197-27205, 1997.

Liou, K., P. T. Newell, C.-I Meng, M. Brittnacher, and G. Parks, Characteristics of the solar wind controlled auroral emissions, J. Geophys. Res., 103, 17543-17557, 1998.

Liou, K., P. T. Newell, C.-I Meng, T. Sotirelis, M. Brittnacher, and G. Parks, The source region of 1500 MLT auroral bright spots:  Simultaneous Polar UV-images and DMSP particle data, J. Geophys. Res., 104, 24587-24602 1999.

Liou, K., C.-I Meng, T. Y. Lui, P. T. Newell, M. Brittnacher, G. D. Reeves, R. R. Anderson, and K. Yumoto, On relative timing in substorm onsets, J. Geophys. Res., 104, 22807-22817, 1999.

Liou, K., C.-I Meng, P. T. Newell, K. Takahashi, S.-I. Ohtani, A. T. Y. Lui, M. Brittnacher, and G. Parks, Evaluation of low-latitude Pi2 pulsations as indicators of substorm onset using Polar ultraviolet imagery, J. Geophys. Res., 105, 2495-2505, 2000a.

Liou, K., C.-I Meng, A. T. Y. Lui, P. T. Newell, and R. R. Anderson, Auroral kilometric radiation at substorm onset, J. Geophys. Res., 105, 25325-25331, 2000b.

Liou, K., C.-I Meng, P. T. Newell, A. T. Y. Lui, and G. Reeves, Particle injections with auroral expansion, J. Geophys. Res., 106, 5873, 2001c.

Liou, K., P. T. Newell, and C.-I Meng, Seasonal effects on auroral particle acceleration and precipitation, J. Geophys. Res., 106., 5531, 2001a.

Liou, K., C.-C. Wu, R. P. Lepping, P. T. Newell, and C.-I Meng, Midday sub-auroral patches (MSPs) associated with interplanetary, Geophys. Res. Lett., 29(16)., 1771, doi:10.1029/2001GL014182, 2002b.

Liou, K., C.-I Meng, A. T. Y. Lui, P. T. Newell, and S. Wing, Magnetic dipolarization with substorm expansion onset, J. Geophys. Res., 107, 1131, doi:10.1029/2001JA000179 , 2002a.

Liou, K., J., P. T. Newell, C.-I Meng, C.-C. Wu, and R. P. Lepping, Investigation of external triggering of substorms with Polar ultraviolet imager observations, J. Geophys. Res., 107., doi:10.1029/2003JA009984, 2003.

Liou, K., P. T. Newell, C.-I Meng, C.-C. Wu, and R. P. Lepping, On the relationship between shock-induced polar magnetic bays and solar wind parameters, J. Geophys. Res., 108., doi:10.1029/2004JA010400, 2004.

Liou, K., J. M. Ruohoniemi, P. T. Newell, R. Greenwald and C. -I Meng, and M. Hairston Observations of ionospheric plasma flows within theta auroras, J. Geophys. Res., 109., A03303, doi:10.1029/2004JA010735, 2005a.

Liou, K., P. T. Newell, B. J. Anderson, L. Zanetti, and C. -I Meng, Neutral composition effects on ionospheric storms at middle and low latitudes, J. Geophys. Res., 109., A05309, doi:10.1029/2004JA010840, 2005b.

Meng, C. -I, K. Liou, P. T. Newell, Asymmetric sunlight effect on dayside/nightside auroral precipitation, Phys. Chem. Earth (c), 26, 43-47, 2001.

Newell, P. T., C.-I Meng, T. Sotirelis, and K. Liou, Polar UVI observations of global auroral power as a function of polar cap size and magnetotail stretching, J. Geophys. Res., 106., 5895, 2001a.

Newell, P. T., K. Liou, T. Sotirelis, and C.-I Meng, Auroral power during substorms:  A Polar UVI based superposed epoch analysis, J. Geophys. Res 106,, 28885-28896, 2001b.

Newell, P. T., T. Sotirelis, J. P. Skura, C.-I. Meng, and W. Lyatsky, Ultraviolet insolation drives seasonal and diurnal space weather variations, J. Geophys. Res., 107, doi:10.1029/2002JA000196, 2002.

Sergeev, V. A., K. Liou, C.-I Meng, P. T. Newell, M. Brittnacher, G. Parks, and G. D. Reeves, Development of auroral streamers in association with localized impulsive injections to the inner magnetotail, Geophys. Res. Lett.,  26, 417-420, 1999.

Shue, J.-H., P. T. Newell, K. Liou, and C.-I Meng, The quantitative relationship between auroral brightness and solar EUV Pedersen conductance, J. Geophys. Res., 106, 5883, 2001a.

Shue, J.-H., P. T. Newell, K. Liou, and C.-I Meng, Interplanetary magnetic field clock angle influence on auroral patterns, J. Geophys. Res., 106, 5913, 2001b.

Shue, J.-H., P. T. Newell, K. Liou, C.-I Meng, and S. W. H. Cowley, Dependence of auroral brightness on the X component of the interplanetary magnetic field, J. Geophys. Res., 107, 1197, doi:10.1029/2001JA/000229, 2002a.

Shue, J.-H., P. T. Newell, K. Liou, C.-I Meng, Y. Kamide, and R. P. Lepping, Two-component auroras,  Geophys. Res. Lett. 29, 1379, doi:10.1029/2002GL014657, 2002b.

Shue, J.-H., S. Ohtani, P. T. Newell, K. Liou, C.-I. Meng, A. Ieda, and T. Mukai, quantitative relationships between plasma sheet fast flows and nightside auroral power,  J. Geophys. Res., 108. ., 1231, doi:10.1029/2002JA009794, 2003.

Wu, C.-C., K. Liou, R. P. Lepping, C.-I Meng,  J. Atmos. Terr. Phys., 66. (2)., 125-132, 2004.