Isual Publications 2014

COM_FABRIK_ORDERpublish time # Citation abstract
200812 91 T. Adachi, S. A. Cummer, J. Li, Y. Takahashi, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, and H. U. Frey( 200812 ).Correlated optical and radio signatures in sprite-producing lightning, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. AE13A-0301

We find a strong correlation between the optical and radio signatures of sprite-producing lightning, which suggests a possible new technique for the estimation of lightning current moment from measurement of optical emission intensity. During the period from 04 July 2004 to 23 June 2007, the ISUAL payload on FORMOSAT-2 satellite has observed 72 sprite events in the American and Caribbean region. In order to clarify the relationship between lightning processes and the generation of sprites, we analyze optical data observed with the ISUAL spectrophotometer and magnetic field data observed at Duke University (35.98 deg N, -79.10 deg E). In the present study, we select 5 sprite events in which the signal-to-noise ratios are sufficiently high both in the optical and electromagnetic data. By correcting instrumental functions and atmospheric transmittance using MODTRAN-4 code, the absolute luminosity of lightning 777.4 nm emissions is estimated. In all of 5 events, we find clear signatures of the return strokes, continuing currents, and M-component processes with luminosities of 100-800, 10-50, and 50-200 (MR), respectively. Concurrent waveforms of current moment change derived from magnetic field data also show corresponding signatures. It is found that the luminosity and current moment in lightning is strongly related with correlation coefficients of 0.774-0.968. To quantify a scaling factor between the luminosity and current moment, we find simple linear functions that best fit the observed data using the least square method. The estimated scaling factors are in the range of 0.66-0.85 (MR/kA-km) with an extraordinary value of 1.67 (MR/kA-km) in one event. We suggest that the lightning current moment, which is an essential parameter for the production of sprites, could be estimated from optical measurements by using a scaling factor of 1.06 (MR/kA-km) within an error of 30-50 %.

200812 92 A. B. Chen, L. Y. Tsai, L. J. Lee, J. K. Chou, H. T. Su, R. R. Hsu, C. C. Wu, P. H. Lin, S. B. Mende, H. U. Frey, Y. Takahashi, and L.C. Lee( 200812 ).Meteorological aspects of elves and jets, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. AE13A-0303

Evidence for ocean-atmosphere-ionosphere coupling is revealed in recent studies of ISUAL transient luminous events (TLEs) [Chen et al., 2008]. The results suggest that the meteorological systems below the stratosphere, primarily driven by sea surface temperature and solar radiation, play essential roles in inducing TLEs between the cloud top and the lower ionosphere. Through analyzing the ISUAL-recorded TLEs since July 2004, we realize that different types of TLEs are likely associated with different meteorological systems. For example, the elves are mainly located above Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ); elves also are strongly correlated with the atmospheric updraft and the precipitation. The fall/winter elves distribute along storm tracks poleward of 30 degrees north or south, implying their association with extratropical cyclones. Numerous blue jets and gigantic jets are recorded around tropical cyclones by ISUAL. Several recent examples indicate that blue jets and lightning often occur in rapid successions in the strong convective regions associated with the spiral rainbands of typhoons or hurricanes. Illustrative data and some of the probable mechanisms will be presented in the conference.

200812 93 L. J. Lee, A. B. Chen, L. Y. Tsai, J. K. Chou, S. C. Chang, C. L. Kuo, H. T. Su, R. R. Hsu, C. C. Wu, P. H. Lin, and L.C. Lee( 200812 ).TLEs, ITCZ, Storm Tracks and Their Correlation, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. AE13A-0316

Between July 2004 and February 2008, ISUAL has recorded 6747 elves, 718 sprites, 783 halos, 1081 blue jets, and 17 gigantic jets. We examine the correlation between the distribution of TLEs and the annual Inter- tropical Convergence Zone (ITCZ) distribution by analyzing the outgoing long-wave radiation (OLR) data from NOAA/ESRL Physical Sciences Division. The results indicate that there are two different TLE distribution patterns. For the low latitude region, the movement of TLEs occurrence follows the seasonal migration of the IITCZ. In northern hemisphere summer, the ITCZ is mainly located to the north of the equator and the distribution of TLEs follows. In southern hemisphere summer, part of ITCZ moves to south of the equator and so does the distribution of TLEs. In the middle and high latitude winter regions, the ISUAL recorded TLEs are defined as the winter TLEs, which are generally associated with cold fronts, air masses and mid-latitude cyclones. From the global distribution of winter TLEs, it is shown that they tend to congregate in some specific regions. Namely, in the northern winter , TLEs concentrate over the Japan Sea , north Pacific Ocean , northwest Atlantic Ocean and Mediterranean Sea ; while in the southern winter , TLEs distribute primarily over the south coast of Australia , south Pacific Ocean and east coast of south America. We find the distribution of winter TLEs is well collocated with the storm tracks. The correlation between the winter TLEs and storm tracks is thus analyzed.

200812 94 S. C. Chang, C. L. Kuo, J. K. Chou, L. Y. Tsai, L. J. Lee, A. B. Chen, H. T. Su, R. R. Hsu, and L.C. Lee( 200812 ).Far-Ultraviolet Emission in ISUAL Recorded TLEs and Lightning Events, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. AE13A-0317

In analyzing events recorded by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL), we often found lightning events that appeared to have Lyman-Birge-Hopfield (LBH) emission (SP1; 150-280nm). Also for most of the seemingly LBH-emitting lightning events, the intensity of LBH emission is substantially lower than their elve-accompanying counterparts. If we further consider the ISUAL detection limit that imposed on by the background fluctuation, then the possibility for these so called pure lightning events to have dim accompanying elves cannot be ruled out. To provide a definitive answer on the lightning LBH emission problem, we will use the ISUAL SP1 as an indicator to study FUV-emitting events that occur in front of Earth limb. So far we have studied the relation between integrated photon flux in 630-750nm image and the corresponding time-integrated photon flux in SP1 for elves and found positive correlation. We are also comparing the peak current of the associated National Lightning Detection Network (NLDN) events and their correlation with ISUAL imager and SP recorded intensities. If the LBH emission in lightning were found to be from dim elves not lightning, then the result implies that the elve occurrence rate is higher than expected.

200812 95 C. L. Kuo, A. B. Chen, S. C. Chang, L. J. Lee, J. K. Chou, L. Y. Tsai, R. R. Hsu, H. T. Su, L.C. Lee, H. U. Frey, S. B. Mende, Y. Takahashi, , , , , , and ( 200812 ).Global energy deposition and chemical effect by transient luminous events in the upper atmosphere, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. AE22A-05

Based on the analysis of the data from the imager of sprites and upper atmospheric lightning (ISUAL) experiment on the FORMOSAT-2 satellite, it has been reported that elve is the most dominant type of transient luminous events (TLEs) and the global occurrence rates of sprites, halos and elves are ~1, ~1 and 35 events/min, respectively [Chen et al, 2008]. In this presentation, we will review some of the important findings in the ISUAL experiment, including the deduction of the reduced E-field in sprites, the comparison of the modeling results with the observed elves, and detailed analyses of gigantic jets. Also through computing the radiative emissions in ISUAL recorded TLE and their energy deposition in the upper atmosphere, we found that for sprites, halos and elves the energy deposition is 22, 14 and 19 MJ per event, respectively. After factoring in the global occurrence rates, the global energy deposition rates in the upper atmosphere are 22, 14 and 665 MJ /min from sprites, halos and elves. Also in-line with the works of Sentman et al. (2008) on the chemical processes in discharge phenomena, we will discuss the possible chemical effects of TLEs in the upper atmosphere.

200812 96 C. Y. Chiang, T. F. Chang, C. Lin, P. K. Rajesh, J. Y. Liu, A. B. Chen, H. T. Su, and R. R. Hsu( 200812 ).ISUAL side-way observations of the OI(1D) night airglows, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. SA43B-1598

Recently, ISUAL/FORMOSAT-2 Satellite has devoted more observation time to investigate the OI(1D) nightglow from the sideway, which provides the first comprehensive survey of 630.0nm emission in the pre- midnight sector at F layer. It is found that the OI(1D) nightglow enhancement exhibited remarkable seasonal variations. In this study, we want to highlight the following three points. First, semiannual anomaly and winter anomaly existed in the form of the brightening emission in the region of equatorial anomaly. Second, the data indicates that the tidally enhanced regions show significant longitudinal variability. Third, the latitudinal variability of OI(1D) nightglow can be contributed to both the Equatorial Ionization Anomaly (EIA) effect and the upward propagation tides.

200812 97 T. F. Chang, C. Z. Cheng, C. Y. Chiang, S. W. Tam, A. B. Chen, R. R. Hsu, and H. T. Su( 200812 ).Azimuthal structure of substorm breakup arcs prior to expansive phase onset using ISUAL/FORMOSAT-2, American Geophysical Union, Fall Meeting 2008, San Francisco, USA. SM43A-1692

Substorm breakup arcs are investigated for substorm onset that occurs at the location of "Harang discontinuity" at pre-midnight. The auroral breakup arc images are obtained by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) onboard FORMOSAT-2 satellite. We identify that the auroral breakup arc brightening occurs at the same time as the associated negative H-Bay and Pi 2 pulsations. It begins with a brightening on the arc and evolves into clear bead-like structure with approximate equally spaced separation along the arc direction. The enhanced auroral arcs finally break up into several parts. The azimuthal mode number of auroral breakup arcs prior to expansive phase onset ranges from ~200 to ~300. Based on the observations, we suggest that the substorm initial breakup arcs are consistent with kinetic ballooning instability, which is localized at the center of cross tail current sheet at about -(8-10) RE for strong substorms.

200905 98 J. K. Chou, C. L. Kuo, L. Y. Tsai, S. C. Chang, L. J. Lee, Y. J. Lee, S. M. Huang, A. B. Chen, H. T. Su, R. R. Hsu, S. A. Cummer, H. U. Frey, S. B. Mende, Y. Takahashi, and L.C. Lee( 200905 ).Positive and Negative Gigantic Jets, AGU Chapman Conference on the Effects of Thunderstorms and Lightning in the Upper Atmosphere, Penn State University, State College, PA, USA. OTL-03

From analyzing the ISUAL recorded gigantic jets (GJs), there possibly are three forms of GJs.
The first type (type-I) is similar to those reported in the ground observations [Pasko, et al., 2002; Su, et al., 2003]. These GJs start from the cloud top and propagate upward. After the GJ completes the discharge channel to the ionosphere, it followed by the trailing jet. The data from ISUAL Imager, spectrophotometers (SP), and array photometers (AP) all indicate that the cloud radiate continuous luminance during the trailing-jet stage.
The second type of GJs (type-II) begins as a blue jet (BJ) that slowly propagates upward and then develops into a GJ. We also found that BJs occurred frequently at the same region before and after the type-II GJs. The ISUAL data shows that type-II GJs are dimmer and their S/N ratio are lower comparing with those for the type-I GJs. During the fully-developed stage, the streamer zone of type-I GJs are averagely ~3.5 times brighter than the type-II.
The third type (type-III) is preceded by lightning, and then develops into a GJ. The brightness of the type-III GJs falls between the type-I and the type-II.
We propose that the first two types of GJs have different discharge polarities. The associated ELF sferics for the ground observed GJs indicates that the type-I GJs are negative cloud-to-ionosphere discharges (-CIs). Type-II GJs are probably comprised of positive streamers (+CIs), similar to those in BJs [Pasko, 2002]. The polarity of type-III GJs is yet to be determined.

200905 99 L. Y. Tsai, S. M. Huang, A. B. Chen, S. C. Chang, J. K. Chou, C. M. Chen, H. T. Su, R. R. Hsu, C. L. Kuo, C. C. Wu, P. H. Lin, R. Holzworth, H. U. Frey, S. B. Mende, Y. Takahashi, and L.C. Lee( 200905 ).Blue Jets Over Tropical Cyclones, AGU Chapman Conference on the Effects of Thunderstorms and Lightning in the Upper Atmosphere, Penn State University, State College, PA, USA. OTL-12

Between 1 January 2005 and 31 December 2008, ISUAL recorded 1176 blue jets. Among them, 76% occurred consecutively and a large fraction of them were associated with tropical cyclones.

This poster showcases Typhoon Fungwong (July 27,2008), which featured interesting interactions between blue jets as positive streamers and two types of lightning (intra-cloud and negative cloud-to-ground). Not only IC flashes act as charge imbalance providers, vertical wind shear at the spiral rainband also seemed to cause the distortion of the charge structure of the thundercloud.

This poster also presents blue jets from tropical cyclones near Taiwan and Australia, due to hemisphere comparison, availability of meteorological data, and their usual high blue jet occurrence rate.

200905 100 A. B. Chen, H. T. Su, R. R. Hsu, C. L. Kuo, Y. J. Lee, L. Y. Tsai, J. K. Chou, L. J. Lee, S. C. Chang, S. B. Mende, H. U. Frey, Y. Takahashi, and L.C. Lee( 200905 ).Spatial and Interannual Variability of Transient Luminous Event and Intense Lightning by ISUAL Experiment, AGU Chapman Conference on the Effects of Thunderstorms and Lightning in the Upper Atmosphere, Penn State University, State College, PA, USA. (invited)

Since the discovery of sprites in 1989, transient luminous events (TLEs; sprites, elves, halos, blue jets, and gigantic jets) were studied extensively by ground observations, remote radio measurements, as well as shuttle observations in the past decades. But the global distribution and seasonal variation of TLEs are still not well assessed due to limitations in previous space or ground observations. Imager of Sprites and Upper Atmospheric Lightnings (ISUAL), the scientific payload onboard FORMOSAT-2 satellite is the first space-borne instrument that dedicates to a long-term and global survey of TLEs. Between July 2004 and January 2009, ISUAL has recorded more than 10,000 TLEs and tens of thousands of intense lightning. The high cumulative TLE event number has allowed us to explore the temporal and regional variations and their relation to the climate variability. The statistic result shows that the seasonal variation of elves distribution closely follows both ITCZ (inter-tropical convergence zone) and the deep updraft regions in the low latitudes. These imply that the latitudinal atmospheric circulation maybe is the primary force driving the production of elves. The occurrence of sprite matches the distribution of lightning in low latitude regions and winter storm tracks in the winter middle latitude regions. Chen et al. [2008] noted that a strong dependency between the elves occurrence and the sea surface temperature; thus implying a strong coupling between ocean, atmosphere and ionosphere may exist, and the El Nino-South Oscillation (ENSO) should play an important role in the variability of TLEs. We also perform a cross comparison of the inter-annual variation of TLEs and the intense lightning with Southern Oscillation Index (SOI), climate variability and sea surface temperature change in a few regions. The result indicates that the variability of TLE and lightning activity are closely governed by the sea surface temperature and the meteorological dynamics in the troposphere.

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