bluuebunny/crossref_metadata_2025 huggingface dataset:
Trend estimation and change point detection in individual climatic series using flexible regression methods
Authors: Bates Bryson C. , Chandler Richard E. , Bowman Adrian W.
Published: July 2012

Over recent years, considerable attention has been given to the problem of detecting trends and change points (discontinuities) in climatic series. This has led to the use of a plethora of detection techniques, ranging from the very simple (e.g., linear regression and t‐tests) to the relatively complex (e.g., Markov chain Monte Carlo methods). However, many of these techniques are quite restricted in their range of application and care is needed to avoid misinterpretation of their results. In this paper we highlight the availability of modern regression methods that allow for both smooth trends and abrupt changes, and a discontinuity test that enables discrimination between the two. Our framework can accommodate constant mean levels, linear or smooth trends, and can test for genuine change points in an objective and data‐driven way. We demonstrate its capabilities using the winter (December–March) North Atlantic Oscillation, an annual mean relative humidity series and a seasonal (June to October) typhoon count series as case studies. We show that the framework is less restrictive than many alternatives in allowing the data to speak for themselves and can give different and more credible results from those of conventional methods. The research findings from such analyses can be used to appropriately inform the design of subsequent studies of temporal changes in underlying physical mechanisms, and the development of policy responses that are appropriate for smoothly varying rather than abrupt climate change (and vice versa).
Carbon dioxide snow clouds on Mars: South polar winter observations by the Mars Climate Sounder
Authors: Hayne Paul O. , Paige David A. , Schofield John T. , Kass David M. , Kleinböhl Armin , Heavens Nicholas G. , McCleese Daniel J.
Published: July 2012

We present south polar winter infrared observations from the Mars Climate Sounder (MCS) and test three hypotheses concerning the origins of “cold spots”: regions of anomalously low infrared brightness temperatures, which could be due to enrichment in non‐condensable gases, low‐emissivity surface frost, or optically thick CO2 clouds. Clouds and surface frosts have been historically difficult to distinguish, but the unique limb sounding capability of MCS reveals extensive tropospheric CO2clouds over the cold spots. We find that both clouds and surface deposits play a significant role in lowering the infrared emissivity of the seasonal ice cap, and the granular surface deposits are likely emplaced by snowfall. Surface temperatures indicate the polar winter atmosphere is enriched by a factor ∼5–7 in non‐condensable gases relative to the annual average, consistent with earlier gamma ray spectrometer observations, but not enough to account for the low brightness temperatures. A large ∼500‐km diameter cloud with visible optical depth ∼0.1–1.0 persists throughout winter over the south polar residual cap (SPRC). At latitudes 70–80°S, clouds and low emission regions are smaller and shorter‐lived, probably corresponding to large‐grained “channel 1” clouds observed by the Mars Orbiter Laser Altimeter. Snowfall over the SPRC imparts the lowest emissivity in the south polar region, which paradoxically tends to reduce net accumulation of seasonal CO2 by backscattering infrared radiation. This could be compensated by the observed anomalously high summertime albedo of the SPRC, which may be related to small grains preserved in a rapidly formed snow deposit.
Spatial distribution of glacial erosion rates in the St. Elias range, Alaska, inferred from a realistic model of glacier dynamics
Authors: Headley Rachel , Hallet Bernard , Roe Gerard , Waddington Edwin D. , Rignot Eric
Published: July 2012

Glaciers have been principal erosional agents in many orogens throughout much of the recent geological past. A modern example is the St. Elias Mountains in southeastern Alaska; it is a highly convergent, complex orogen, which has been glaciated for much of its history. We examine the Seward‐Malaspina Glacier system, which comprises two of the largest temperate glaciers in the world. We focus on the pattern of erosion within its narrow passage through the St. Elias Mountains, the Seward Throat. Measured glacier surface velocities and elevations provide constraints for a full‐stress numerical flowband model that enables us to quantitatively determine the glacier thickness profile, which is not easily measured on temperate glaciers, and the basal characteristics relevant for erosion. These characteristics at the bed, namely the water pressure, normal and shear stresses, and sliding velocity, are then used to infer the spatial variation in erosion rates using several commonly invoked erosion laws. The calculations show that the geometry of the glacier basin exerts a far stronger control on the spatial variation of erosion rates than does the equilibrium line altitude, which is often assumed to be important in studies of glaciated orogens. The model provides a quantitative basis for understanding why erosion rates are highest around the Seward Throat, which is generally consistent with local and large‐scale geological observations and thermochronologic evidence. Moreover, model results suggest how glacier characteristics could be used to infer zones of active or recent uplift in ice‐mantled orogens.
Australian developments in marine science
Authors: Coffin Millard F.
Published: July 2012

Australia is an island nation with about two thirds of its jurisdiction underwater. On 25 May 2012, Australia instituted the Seas and Submerged Lands (Limits of Continental Shelf) Proclamation 2012, confirming areas of seabed where Australia has exclusive rights to explore and exploit marine resources. This proclamation follows recommendations by the Commission on the Limits of the Continental Shelf, a body established under the United Nations Convention on the Law of the Sea, confirming Australia's entitlement to extended continental shelf, i.e., that beyond 200 nautical miles from the coastline, of some 2.56 million square kilometers, excluding Australian Antarctic Territory [Symonds et al., 2009] (Figure 1a).
With Scripps library closure, university tries to minimize impact
Authors: Showstack Randy
Published: July 2012

The Scripps Institution of Oceanography (SIO) Library at the University of California, San Diego (UCSD) closed on 29 June, succumbing to budget cuts and a change in library usage that has included a shift toward electronic media and fewer people using the library's physical facilities. The SIO library's book and journal collections—which include more than 227,000 volumes and more than 700 print periodicals—will be transferred to UCSD's Geisel Library about 1 mile away; the Scripps archives and special collections will remain in their current location in the Eckart Building at SIO, according to a UCSD announcement. A note posted on the UCSD library Web site states, “Though Scripps Institution of Oceanography loses a library facility on campus, the UC San Diego Library remains committed to supporting Scripps faculty, staff and students, and continues to develop electronic and print collections to support the Institution's academic mission. Research and curriculum support services also continue to be available, by appointment.”
Quantifying the value of environmental information to society
Authors: Craglia Max , Friedl Lawrence , Pearlman Jay
Published: July 2012

Socio‐Economic Benefits From the Use of Earth Observation; Ispra, Italy, 11–13 July 2011 Many large space‐or ground‐based Earth observation systems, such as Global Monitoring for Environment and Security (GMES) and Landsat, are justified by citing their benefits to scientific knowledge and their impacts on government decisions about environmental issues. These justifications attempt to quantify the lives saved, losses avoided, or economic benefits gained. Each justification is made on an ad hoc basis, and the approach used in one case rarely applies to another. In July 2011 a workshop was held at the European Commission Joint Research Centre in Italy to consider whether broadly applicable methodologies could be developed that could be consistently used for assessing the value of large‐scale observation and information systems.
A call to public service
Authors: Lloyd Ian
Published: July 2012

Working for a U.S. senator (Sen. Jeff Merkley (D‐Oreg.)) as a 2011–2012 AGU Congressional Science Fellow has affirmed my conviction that more scientists and engineers should be working in Congress and other branches of government. I am not referring to scientists who provide specialized, research‐oriented services and communicate technical information, which is important. I am referring to people with scientific and technical backgrounds who should work on policy issues in government if they are interested in doing so. Scientists can be proficient in this type of work because of the way they think about problems, not just because of the technical knowledge they can contribute, however relevant it may be.
Outstanding Student Paper Awards
Authors: Anonymous
Published: July 2012

The following members received Outstanding Student Paper Awards at the 2011 AGU Fall Meeting in San Francisco, Calif. See also “Outstanding Student Paper Awards” published previously (Eos, 93(27), 253–254; Eos, 93(28), 260–261) and in future issues of Eos.
Conference focuses on challenges, opportunities in key Earth science and policy topics
Authors: Landau Elizabeth , Hankin Erik , Uhlenbrock Kristan
Published: July 2012

In our rapidly changing world, integrating Earth and space science into policy is vital to supporting our economy, public safety, and national security. One way in which AGU is striving to bridge the science and policy fields is through discussions and collaborations at the AGU Science Policy Conference. This inaugural conference, held in May 2012 in Washington, D. C., featured experts from government, industry, academia, and nonprofits. The goal of this new conference is to ensure diverse discussions and viewpoints on the challenges and opportunities of science policy, with a focus on applications of Earth and space science that serve local, national, and international communities.
Three featured plenary sessions
Authors: Anonymous
Published: July 2012

The conference included three plenary sessions. The plenary on Governance, Security, Economy, and the Ecosystem of the Changing Arctic featured Vera Alexander, president, Arctic Research Consortium of the U.S.; Alan Thornhill, chief environmental officer, U.S. Department of the Interior's Bureau of Ocean Energy Management; and Fran Ulmer, chair, U.S. Arctic Research Commission. A plenary on the U.N. Convention on the Law of the Sea featured Ambassador David Balton, deputy assistant secretary for oceans and fisheries, U.S. Department of State; and Rear Admiral Frederick Kenney Jr., judge advocate general and chief counsel, U.S. Coast Guard. The plenary on Science and the 21st Century featured Phil Keslin, chief technology officer, small lab within Google.
Presidential Citation for Science and Society
Authors: Anonymous
Published: July 2012

AGU presented its Presidential Citation for Science and Society to three recipients at a reception on 1 May 2012 in the Rayburn House Office Building as part of the inaugural AGU Science Policy Conference. Google Earth, Jane Lubchenco, who is the under secretary of Commerce for oceans and atmosphere and administrator of the National Oceanic and Atmospheric Administration, and Sen. Olympia Snowe (R‐Maine) were recognized for their leadership and vision in shaping policy and heightening public awareness of the value of Earth and space science. “This is an important award because with it AGU brings to light the importance of cutting‐edge use‐inspired science that helps people, communities, and businesses adapt to climate change and sustainably manage our oceans and coasts,” Lubchenco said.
Clouds continue to plague latest generation climate models
Authors: Schultz Colin
Published: July 2012

In anticipation of the 2013 publication of the Intergovernmental Panel on Climate Change's fifth assessment report, many in the climate modeling community came together in 2008 under the banner of the Fifth Coupled Model Intercomparison Project (CMIP5). An international effort, this project sought to identify crucial research directions and laid down standardized parameters under which atmosphere‐ocean coupled general circulation models (AOGCMs) should be tested so that they can be compared on equal footing. Andrews et al. assessed 15 models participating in the CMIP5 to find the most up‐to‐date measure of climate sensitivity and the remaining sources of model uncertainty. To test the AOGCMs, the authors looked at how the modeled top‐of‐the‐atmosphere (TOA) radiative emissions from the Earth respond to an imposed change in atmospheric carbon dioxide concentration. Because TOA emissions depend on the global mean atmospheric and surface temperatures, this technique provides an effective way to investigate the feedback mechanisms built into each of the models. The authors assessed model runs for pre‐industrial atmospheric carbon dioxide levels as well as those that simulated a sudden quadrupling in the concentration of atmospheric carbon dioxide—the amount that could be reached given a “do nothing” approach to mitigating carbon emissions.
Italian super‐eruption larger than thought
Authors: Schultz Colin
Published: July 2012

Recent research suggested that the super‐eruption of the Campi Flegrei caldera volcano in southern Italy about 40,000 years ago may have played a part in wiping out, or forcing the migration of, the Neanderthal and modern human populations in the eastern Mediterranean regions that were covered in ash. Now a new modeling study by Costa et al. suggests that this eruption may have been even larger than previously thought. This Campi Flegrei eruption produced a widespread ash layer known as Campanian Ignimbrite (CI). Using ash thickness measurements collected at 115 sites and a three‐dimensional ash dispersal model, the researchers found that the CI super‐eruption would have spread 250–300 cubic kilometers of ash across a 3.7‐million‐square kilometer region—2 to 3 times previous ash volume estimates.
Effects of variable magma supply on mid‐ocean ridge eruptions: Constraints from mapped lava flow fields along the Galápagos Spreading Center
Authors: Colman Alice , Sinton John M. , White Scott M. , McClinton J. Timothy , Bowles Julie A. , Rubin Kenneth H. , Behn Mark D. , Cushman Buffy , Eason Deborah E. , Gregg Tracy K. P. , Grönvold Karl , Hidalgo Silvana , Howell Julia , Neill Owen , Russo Chris
Published: July 2012

Mapping and sampling of 18 eruptive units in two study areas along the Galápagos Spreading Center (GSC) provide insight into how magma supply affects mid‐ocean ridge (MOR) volcanic eruptions. The two study areas have similar spreading rates (53 versus 55 mm/yr), but differ by 30% in the time‐averaged rate of magma supply (0.3 × 106 versus 0.4 × 106 m3/yr/km). Detailed geologic maps of each study area incorporate observations of flow contacts and sediment thickness, in addition to sample petrology, geomagnetic paleointensity, and inferences from high‐resolution bathymetry data. At the lower‐magma‐supply study area, eruptions typically produce irregularly shaped clusters of pillow mounds with total eruptive volumes ranging from 0.09 to 1.3 km3. At the higher‐magma‐supply study area, lava morphologies characteristic of higher effusion rates are more common, eruptions typically occur along elongated fissures, and eruptive volumes are an order of magnitude smaller (0.002–0.13 km3). At this site, glass MgO contents (2.7–8.4 wt. %) and corresponding liquidus temperatures are lower on average, and more variable, than those at the lower‐magma‐supply study area (6.2–9.1 wt. % MgO). The differences in eruptive volume, lava temperature, morphology, and inferred eruption rates observed between the two areas along the GSC are similar to those that have previously been related to variable spreading rates on the global MOR system. Importantly, the documentation of multiple sequences of eruptions at each study area, representing hundreds to thousands of years, provides constraints on the variability in eruptive style at a given magma supply and spreading rate.
Heat flow in the Lesser Antilles island arc and adjacent back arc Grenada basin
Authors: Manga Michael , Hornbach Matthew J. , Le Friant Anne , Ishizuka Osamu , Stroncik Nicole , Adachi Tatsuya , Aljahdali Mohammed , Boudon Georges , Breitkreuz Christoph , Fraass Andrew , Fujinawa Akihiko , Hatfield Robert , Jutzeler Martin , Kataoka Kyoko , Lafuerza Sara , Maeno Fukashi , Martinez‐Colon Michael , McCanta Molly , Morgan Sally , Palmer Martin R. , Saito Takeshi , Slagle Angela , Stinton Adam J. , Subramanyam K. S. V. , Tamura Yoshihiko , Talling Peter J. , Villemant Benoit , Wall‐Palmer Deborah , Wang Fei
Published: July 2012

Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m2 on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to <0.07 W/m2 at distances >15 km from the crest in the back arc direction. Combined with previous measurements, we find that the magnitude and spatial pattern of heat flow are similar to those at continental arcs. The heat flow in the Grenada basin to the west of the active arc is 0.06 W/m2, a factor of 2 lower than that found in the previous and most recent study. There is no thermal evidence for significant shallow fluid advection at any of these sites. Present‐day volcanism is confined to the region with the highest heat flow.
Can tidal tomography be used to unravel the long‐wavelength structure of the lunar interior?
Authors: Zhong Shijie , Qin Chuan , A Geruo , Wahr John
Published: July 2012

The Moon displays a number of hemispherically asymmetric features that may be related to long‐wavelength structure and dynamics in the lunar mantle. Here we propose to use observations of the non‐degree‐2 gravitational response of the Moon to degree‐2 tidal forcing to constrain the long‐wavelength lunar mantle structure. For a planetary body with laterally varying structure, degree‐2 tidal forces excite gravitational response at non‐degree‐2 harmonics due to mode coupling effects. Using a new numerical model, we determine that for a lunar mantle with ∼5% hemispherical variations in seismic shear wave velocityVs, the degree‐3 response could reach ∼2% of the degree‐2 response. The larger the hemispherical variations inVs, the larger the degree‐3 response. We suggest that if observations from recent lunar missions such as SELENA and GRAIL could be used to determine the non‐degree‐2 tidal response, it might be possible to place constraints on the lunar mantle structure.
Solar influence on winter severity in central Europe
Authors: Sirocko Frank , Brunck Heiko , Pfahl Stephan
Published: July 2012

The last two winters in central Europe were unusually cold in comparison to the years before. Meteorological data, mainly from the last 50 years, and modelling studies have suggested that both solar activity and El Niño strength may influence such central European winter coldness. To investigate the mechanisms behind this in a statistically robust way and to test which of the two factors was more important during the last 230 years back into the Little Ice Age, we use historical reports of freezing of the river Rhine. The historical data show that 10 of the 14 freeze years occurred close to sunspot minima and only one during a year of moderate El Niño. This solar influence is underpinned by corresponding atmospheric circulation anomalies in reanalysis data covering the period 1871 to 2008. Accordingly, weak solar activity is empirically related to extremely cold winter conditions in Europe also on such long time scales. This relationship still holds today, however the average winter temperatures have been rising during the last decades.
Flux of carbonate melt from deeply subducted pelitic sediments: Geophysical and geochemical implications for the source of Central American volcanic arc
Authors: Tsuno Kyusei , Dasgupta Rajdeep , Danielson Lisa , Righter Kevin
Published: July 2012

We determined the fluid‐present and fluid‐absent near‐solidus melting of an Al‐poor carbonated pelite at 3–7 GPa, to constrain the possible influence of sediment melt in subduction zones. Hydrous silicate melt is produced at the solidi at 3–4 GPa whereas Na‐K‐rich carbonatite is produced at the solidi at ≥5 GPa for both starting compositions. At ≥5 GPa and 1050°C, immiscible carbonate and silicate melts appear with carbonate melt forming isolated pockets embedded in silicate melt. Application of our data to Nicaraguan slab suggests that sediment melting may not occur at sub‐arc depth (∼170 km) but carbonatite production can occur atop slab or by diapiric rise of carbonated‐silicate mélange zone to the mantle wedge at ∼200–250 km depth. Flux of carbonatite to shallower arc‐source can explain the geochemistry of Nicaraguan primary magma (low SiO2and high CaO, Ba/La). Comparison of carbonate‐silicate melt immiscibility field with mantle wedge thermal structure suggests that carbonatite might temporally be trapped in viscous silicate melt, and contribute to seismic low‐velocity zone at deep mantle wedge of Nicaragua.
Evaluating global climate responses to different forcings using simple indices
Authors: Drost Frank , Karoly David
Published: July 2012

Previous studies have shown that various climate indices based on surface temperature can be used in detection and attribution studies of climate change. Besides global mean surface temperature, these indices are the contrast between surface temperature over land and over oceans, the temperature contrast between the Northern and Southern Hemispheres, the meridional temperature gradient in the Northern Hemisphere and the magnitude of the annual cycle of temperatures over land. The indices vary independently from the global mean at decadal timescales, yet show common responses to anthropogenic climate change. Collectively they are more useful in detecting and attributing climate change than global mean surface temperature alone. We use CMIP5 model data and investigate to what extent observed trends in surface temperature can be attributed to natural and anthropogenic forcings. The multi‐model ensemble mean trend for all indices, except for NS, are either at or exceed the 5%–95% confidence interval for no trend. These trends cannot be explained by natural forcings only and additional forcings are required to replicate observed trends. Historical simulations with greenhouse gas forcings only resulted generally in trends in the indices that were larger than those in simulations with all historical forcings and observed. The difference in the trends in the indices between the simulations with all historical forcings and with greenhouse gas forcing only are ascribed to the effect of aerosols.
Maximum wind speeds and US hurricane losses
Authors: Murnane R. J. , Elsner J. B.
Published: July 2012

There is academic, commercial, and public interest in estimating loss from hurricanes striking land and understanding how loss might change as a result of future variations in climate. Here we show that the relationship between wind speed and loss is exponential and that loss increases with wind speed at a rate of 5% per m s−1. The relationship is derived using quantile regression and a data set comprising wind speeds of hurricanes hitting the United States and normalized economic losses. We suggest that the “centercepts” for the different quantiles account for exposure‐related factors such as population density, precipitation, and surface roughness, and that once these effects are accounted for, the increase in loss with wind speed is consistent across quantiles. An out‐of‐sample test of this relationship correctly predicts economic losses from Hurricane Irene in 2011. The exponential relationship suggests that increased wind speeds will produce significantly higher losses; however, increases in exposed property and population are expected to be a more important factor for near future losses.
Influence of bias correction on simulated landcover changes
Authors: McAfee Stephanie A. , Russell Joellen L. , Webb Robert S.
Published: July 2012

Vegetation responses to climate change will provide feedbacks that could amplify or moderate regional temperature and precipitation changes. However, systematic biases in the simulation of regional climate across general circulation models (GCMs) may lead to consistent misrepresentation of vegetation changes and associated ecological processes. This study uses Köppen classification driven by simulated climate with and without bias correction. Our results indicate that because climate biases lead to inaccuracies in land cover, corrected and uncorrected analyses result in distinct land cover changes in regions (the tropics and high‐latitude Northern Hemisphere) that have strong climate feedbacks, even though the climate change is identical. While a more realistic biosphere may ameliorate some model biases, our results illustrate the potential for existing errors to influence feedbacks and suggest that, as models become more complex, nuanced understanding of bias propagation will be critical in assessing the uncertainty of projections and common downscaling techniques.
On the sunrise oscillation of the F region in the equatorial ionosphere
Authors: Ambili K. M. , St.‐Maurice J.‐P. , Choudhary R. K.
Published: July 2012

This paper shows that, contrary to previous explanations, the apparent undulating motion of the equatorial F region peak at sunrise is produced by photochemistry rather than dynamics. Our study is based on an investigation of the behavior of the early morning ionosphere observed by a Digital Ionosonde at Trivandrum, India. The phenomenon is rooted in the production of new plasma at the upper F region altitudes soon after sunrise. As the peak photoproduction rate moves down in altitude and increases in magnitude the newly formed plasma follows a similar trend. Once the density becomes large enough to be detected by an ionosonde, a jump is observed in the F region peak altitude. The jump is followed by a quick downward motion of the increasingly strong F peak. Chemistry causes the downward motion of the F peak to end near 250 km. Electrodynamics is not responsible for the sunrise undulation, but plays an indirect role in the detection of the sunrise effect by simultaneously lowering during the night the peak height and decreasing the density. When detectable, the remnant plasma introduces a lower peak height that facilitates the observation of the initial increase in peak height, while the lower background density allows the relatively small initial density increase from photoionization to be observed.
Dispersive modeling of the 2009 Samoa tsunami
Authors: Zhou Hongqiang , Wei Yong , Titov Vasily V.
Published: July 2012

In this study, we investigate the dispersive effects in the 2009 Samoa tsunami through numerical simulations. The wave propagation is first simulated with a weakly nonlinear and dispersive Boussinesq model and a non‐dispersive shallow‐water‐equations model. Comparison of the numerical results between these models indicates that tsunami propagation is significantly affected by the frequency dispersion east of Tonga Trench. Neglecting dispersive effects results in larger wave heights and speeds. The strong frequency dispersion is primarily attributed to the dramatic variation of water surface elevations generated by the earthquake doublet, and enhanced by the uneven bathymetry in Tonga Trench. Tsunami propagation is also simulated with MOST (“Method of Splitting Tsunamis”), which is based on the shallow water equations but uses numerical dispersion to mimic physical frequency dispersion at operational resolutions. A good agreement is observed between MOST and the Boussinesq model, as well as the field measurements in the leading wave. In the shorter trailing waves, agreement becomes poorer due to the mismatch between numerical and physical dispersions.
Midnight ionosphere collapse at Arecibo and its relationship to the neutral wind, electric field, and ambipolar diffusion
Authors: Gong Yun , Zhou Qihou , Zhang Shaodong , Aponte Nestor , Sulzer Michael , Gonzalez Sixto
Published: July 2012

We report the analysis of “midnight collapse,” a large drop in the F‐layer peak height (HmF2) around midnight, observed at Arecibo during Jan. 14–22, 2010. During the nine nights of observations, the first four nights (Jan. 14–17) exhibited modest drops in HmF2 while the last five nights (Jan. 18–22) showed more severe drops. We examine the roles played by the meridional wind, electric field, and ambipolar diffusion in driving the vertical ion motion. The collapse process can be classified into three stages: preconditioning, initial descent, and sustained descent. Severe collapses occur when HmF2 is preconditioned high prior to the collapse. Ambipolar diffusion is most important during the initial descent. Neutral wind and electric field are responsible for sustaining the collapse. During Jan. 18–22, HmF2 was pushed high by the neutral wind before the collapse started. Neutral wind and electric field were in phase during the sustained severe collapses. The diurnal tide of the meridional wind provided the general condition for the collapses. The terdiurnal tide was most important to cause the difference between the two periods in our observation. Previous studies largely emphasized meridional wind being the dominant mechanism causing midnight collapse. Our study suggests that electric field and ambipolar diffusion also play an important role and the former can be the most dominant factor in some cases.
Comparing the cross polar cap potentials measured by SuperDARN and AMIE during saturation intervals
Authors: Gao Ye
Published: July 2012

Assimilative Mapping of Ionospheric Electrodynamics (AMIE) and Super Dual Auroral Radar Network (SuperDARN) are two commonly used techniques to measure cross polar cap potential (ΦPC). In this study, I compare ΦPC inferred from AMIE with that inferred from SuperDARN during saturation intervals. Measurements from Defense Meteorological Satellite Program (DMSP) and polar cap (PC) index are also used to help estimate true ΦPC. Seven saturation events in 2000 were selected. For each event, I ran the AMIE software driven by magnetometer data only, by magnetometer data and SuperDARN data, and by SuperDARN data only. Then I compared ΦPC obtained from AMIE with that from SuperDARN. I found that: (1) ΦPC inferred from SuperDARN is significantly lower than that inferred from other techniques including AMIE when ΦPC is large (e.g., greater than 150 kV); (2) ΦPC inferred from AMIE with SuperDARN input is much higher than ΦPC inferred from SuperDARN; (3) ΦPC inferred from AMIE with magnetometer input tends to give the same results as that inferred from AMIE with magnetometer and SuperDARN input; (4) ΦPC inferred from AMIE with magnetometer input is, in general, in agreement with ΦPCinferred from AMIE with SuperDARN input. It is suggested that reason for the low values of SuperDARN‐derived ΦPC during saturation intervals is that the SuperDARN algorithm to compute ΦPC from measurements is not applicable to such intervals.
On post‐midnight field‐aligned irregularities observed with a 30.8‐MHz radar at a low latitude: Comparison withF‐layer altitude near the geomagnetic equator
Authors: Nishioka M. , Otsuka Y. , Shiokawa K. , Tsugawa T. , Effendy  , Supnithi P. , Nagatsuma T. , Murata K. T.
Published: July 2012

We investigated the relationship between post‐midnightF‐region field aligned irregularities (FAIs) andF‐layer altitude by analyzing data of a 30.8‐MHz radar installed 5at Kototabang, Indonesia (0.2°S, 100.3°E; geomagnetic latitude 10.4°S) and an ionosonde installed at Chumphon, Thailand (10.7°N, 99.4°E; geomagnetic latitude 3.3°N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of theF‐layer rose at Chumphon a half hour before the post‐midnight FAIs appeared at Kototabang. The Doppler velocity of theE‐region FAIs observed simultaneously by the 30.8‐MHz radar was downward, indicating that theF‐layer uplift was not caused by the electric field. We also investigated seasonal variations of the post‐midnight FAI occurrence and theF‐layer altitude. Both the post‐midnight FAIs and the uplift of theF‐layer were frequently seen around midnight between May and August. The seasonal variation of the midnightF‐layer uplift around the geomagnetic equator coincided with that of the post‐midnight FAI occurrence at Kototabang. These results suggest that the uplift of theF‐layer would play an important role in the generation of post‐midnight FAIs. We evaluated the linear growth rate of the Rayleigh‐Taylor instability based on the altitude of theF‐layer observed at Chumphon. The result shows that the uplift of theF‐layer can enhance the growth rate because gravity‐driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the upliftedF‐layer.
An examination of inter‐hemispheric conjugacy in a subauroral polarization stream
Authors: Kunduri B. S. R. , Baker J. B. H. , Ruohoniemi J. M. , Clausen L. B. N. , Grocott A. , Thomas E. G. , Freeman M. P. , Talaat E. R.
Published: July 2012

During geomagnetically disturbed conditions the midlatitude ionosphere is subject to intense poleward directed electric fields in the dusk‐midnight sector. These electric fields lead to the generation of a latitudinally narrow westward directed flow channel in the subauroral region called a subauroral polarization stream (SAPS). If the magnetic field lines are treated as equipotentials, electrodynamic events such as SAPS are expected to occur simultaneously at magnetically conjugate locations with similar features. In this paper we present simultaneous observations of a SAPS event in both hemispheres made by midlatitude SuperDARN radars with conjugate fields‐of‐view. We analyze the relation between the geomagnetic conditions and the characteristics of the channels such as latitudinal location, electric field, total potential variations across the channels, and Pedersen current. The results suggest a strong correlation between the strength of the ring current and the latitudinal location of the channel. An inter‐hemispheric comparison of the characteristics of the channel indicates that the potential variations across the channels are similar while the electric fields, Pedersen currents and latitudinal widths of the channel exhibit differences that are consistent with equal potential variations. We attribute these differences to seasonal differences in ionospheric conductivity between the hemispheres and magnetic distortion effects in the inner magnetosphere.
Survey of coherent ∼1 Hz waves in Mercury's inner magnetosphere from MESSENGER observations
Authors: Boardsen Scott A. , Slavin James A. , Anderson Brian J. , Korth Haje , Schriver David , Solomon Sean C.
Published: July 2012

We summarize observations by the MESSENGER spacecraft of highly coherent waves at frequencies between 0.4 and 5 Hz in Mercury's inner magnetosphere. This survey covers the time period from 24 March to 25 September 2011, or 2.1 Mercury years. These waves typically exhibit banded harmonic structure that drifts in frequency as the spacecraft traverses the magnetic equator. The waves are seen at all magnetic local times, but their observed rate of occurrence is much less on the dayside, at least in part the result of MESSENGER's orbit. On the nightside, on average, wave power is maximum near the equator and decreases with increasing magnetic latitude, consistent with an equatorial source. When the spacecraft traverses the plasma sheet during its equatorial crossings, wave power is a factor of 2 larger than for equatorial crossings that do not cross the plasma sheet. The waves are highly transverse at large magnetic latitudes but are more compressional near the equator. However, at the equator the transverse component of these waves increases relative to the compressional component as the degree of polarization decreases. Also, there is a substantial minority of events that are transverse at all magnetic latitudes, including the equator. A few of these latter events could be interpreted as ion cyclotron waves. In general, the waves tend to be strongly linear and characterized by values of the ellipticity <0.3 and wave‐normal angles peaked near 90°. Their maxima in wave power at the equator coupled with their narrow‐band character suggests that these waves might be generated locally in loss cone plasma characterized by high values of the ratio β of plasma pressure to magnetic pressure. Presumably both electromagnetic ion cyclotron waves and electromagnetic ion Bernstein waves can be generated by ion loss cone distributions. If proton β decreases with increasing magnetic latitude along a field line, then electromagnetic ion Bernstein waves are predicted to transition from compressional to transverse, a pattern consistent with our observations. We hypothesize that these local instabilities can lead to enhanced ion precipitation and directly feed field‐line resonances.
Solar wind alpha particles and heavy ions in the inner heliosphere observed with MESSENGER
Authors: Gershman Daniel J. , Zurbuchen Thomas H. , Fisk Lennard A. , Gilbert Jason A. , Raines Jim M. , Anderson Brian J. , Smith Charles W. , Korth Haje , Solomon Sean C.
Published: July 2012

The Fast Imaging Plasma Spectrometer (FIPS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has made the first in situ measurements of solar wind plasma in the inner heliosphere since the Helios 1 and 2 spacecraft in the 1980s. Although the core of the solar wind velocity distribution is obstructed by the spacecraft sunshade, a data analysis technique has been developed that recovers both bulk and thermal speeds to 10% accuracy and provides the first measurements of solar wind heavy ions (mass per charge >2 amu/e) at heliocentric distances within 0.5 AU. Solar wind alpha particles and heavy ions appear to have similar mean flow speeds at values greater than that of the protons by approximately 70% of the Alfvén speed. From an examination of the thermal properties of alpha particles and heavier solar wind ions, we find a ratio of the temperature of alpha particles to that of protons nearly twice that of previously reported Helios observations, though still within the limits of excessive heating of heavy ions observed spectroscopically close to the Sun. Furthermore, examination of typical magnetic power spectra at the orbits of MESSENGER and at 1 AU reveals the lack of a strong signature of local resonant ion heating, implying that a majority of heavy ion heating could occur close to the Sun. These results demonstrate that the solar wind at ∼0.3 AU is a blend of the effects of wave–particle interactions occurring in both the solar corona and the heliosphere.
On the formation of pre‐onset azimuthal pressure gradient in the near‐Earth plasma sheet
Authors: Xing X. , Lyons L. R. , Zhou X.‐Z. , Angelopoulos V. , Donovan E. , Larson D. , Carlson C. , Auster U.
Published: July 2012

Xing et al. (2011) demonstrated by case study that the plasma sheet pressure gradient at ∼11 REnear the substorm onset meridian undergoes a substantial duskward enhancement shortly before substorm onset as identified from the auroral poleward expansion. It was suggested that the increased upward FAC driven by this pressure gradient enhancement lead to the thin onset arc intensification from which the poleward expansion initiates. In the present study, we employ the multiTHEMIS spacecraft in azimuthal conjunction ‐at ∼−11 REand examine the ion flux and distributions during the period of pressure gradient enhancement, and identify two categories of events. For events with pressure gradient change ≤2 min prior to onset, strong earthward ion flux enhancements covering the energy range from several keV to above 25 keV were observed by the spacecraft identifying the higher pressure increase, while at the same time the ion distributions show a substantial earthward shift in velocity space. These resemble the ion acceleration ahead of earthward moving dipolarization fronts. On the other hand, the spacecraft observing the lower pressure increase found weaker or no ion flux enhancements and had nearly isotropic distributions, indicating that longitudinally localized dipolarization fronts are responsible for the pressure gradient development. These pressure gradient enhancements were in the duskward (dawnward) direction for measurements to the east (west) of the onset region. For pressure gradient enhancement >2 min prior to onset, stronger plasma sheet thinning was observed by the spacecraft identifying the larger pressure increase and the ion distributions appear nearly isotropic, which suggests plasma redistribution in the undisturbed plasma sheet. These two categories suggest that both dipolarization fronts and growth phase plasma sheet localized thinning can drive azimuthal pressure gradient enhancement near the onset meridian and cause pre‐onset thin auroral arc intensification, though the dipolarization front events appear to be substantially more common based on our 14 events.
Ionospheric Joule heating and Poynting flux in quasi‐static approximation
Authors: Vanhamäki H. , Yoshikawa A. , Amm O. , Fujii R.
Published: July 2012

Energy flow is an important aspect of magnetosphere‐ionosphere coupling. Electromagnetic energy is transported as Poynting flux from the magnetosphere to the ionosphere, where it is dissipated as Joule heating. Recently Richmond derived an “Equipotential Boundary Poynting Flux (EBPF) theorem”, that the Poynting flux within a flux tube whose boundary is an equipotential curve is dissipated inside the ionospheric foot point of the flux tube. In this article we study Richmond's EBPF theorem more closely by considering the curl‐free and divergence‐free parts as well as the Hall and Pedersen parts of the ionospheric current system separately. Our main findings are that i) divergence‐free currents are on average dissipationless, ii) the curl‐free Pedersen current is responsible for the whole ionospheric Joule heating and iii) pointwise match between vertical Poynting flux and ionospheric Joule heating is broken by gradients of Hall and Pedersen conductances. Results i) and ii) hold when integrated over the whole ionosphere or any area bounded by an equipotential curve. The present study is limited to quasi‐static phenomena. The more general topic of electrodynamic Joule heating and Poynting flux, including inductive effects, will be addressed in a future study.
Energy transport by kinetic‐scale electromagnetic waves in fast plasma sheet flows
Authors: Chaston C. C. , Bonnell J. W. , Clausen L. , Angelopoulos V.
Published: July 2012

We report observations from the THEMIS spacecraft characterizing the nature and importance of low frequency electromagnetic fluctuations on kinetic scales embedded within fast flows in the Earth's plasma sheet. A consideration of wave property variations with frequency and flow speed suggest that for spacecraft frame frequencies satisfying |vf|/ñi ≤ ùsc ≤ 100|vf|/ñi (or 0.2 ≲ fsc ≲ 20 Hz) these fluctuations can generally be described as kinetic Alfvén waves. Here vf is the flow speed, ñi the ion gyroradius, and ùsc and fsc are the angular and cyclical frequencies respectively in the spacecraft frame. The statistics of energy transport via Poynting flux (S) in these fluctuations and ion energy flux (å) in the flow follow log normal distributions with mean values of 〈S〉 = 101.1 ± 0.7 and 〈ε〉 = 102.4 ± 0.4 mW/m2 respectively where the values are ‘mapped’ to a reference magnetic field at 100 km altitude. Here the indices following ‘ ± ’ correspond to one standard deviation. We find that 〈S/ε〉 = 10−1.3 ± 0.7 or that kinetic Alfvén waves on average transport ∼5% of the total energy transport in the flow but note that the values larger than 25% are within one standard deviation of the mean. Our observations show that these waves are continually radiated outward from the flow toward the auroral oval, low latitude boundary layer or lobes and that over several Earth‐radii the integrated energy loss from the flow channel can be comparable to the total energy content of the flow itself. We find that this plasma sheet energy loss process is particularly effective within |XGSE| ≤ 15 RE.
Nonlinear pitch angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere
Authors: Omura Yoshiharu , Zhao Qinghua
Published: July 2012

We derive the second‐order resonance condition for interaction between a relativistic electron and a coherent Electromagnetic Ion Cyclotron (EMIC) wave with a variable frequency. We perform test particle simulations of relativistic electrons interacting with EMIC waves with a fixed frequency and a rising‐tone frequency such as EMIC triggered emissions observed in the inner magnetosphere. Trapping of resonant electrons leads to rapid and efficient pitch angle scattering of relativistic electrons, resulting in bursty precipitation of relativistic electrons. The efficiency of the pitch angle scattering depends on the gradient of the magnetic field, the frequency sweep rate, and the wave amplitude. The effective wave trapping occurs for a wide range of pitch angles from 10 to 60 degrees. The most effective pitch angle scattering takes place for the case of a rising‐tone emission with an enhanced magnetic field gradient. Since the efficiency of pitch angle scattering also depends on the wave amplitude, resonant electrons may not be scattered into the loss cone in a single passage through the wave packet. However, repeated interactions with a series of wave packets result in scattering of relativistic electrons into the loss cone.
Magnetic declination and zonal wind effects on longitudinal differences of ionospheric electron density at midlatitudes
Authors: Zhang Shun‐Rong , Foster John C. , Holt John M. , Erickson Philip J. , Coster Anthea J.
Published: July 2012

A prominent ionospheric longitudinal variation at midlatitudes, in particular, over the continental US, was found recently. This variation is characterized as a higher east‐side electron density in the evening and a higher west‐side electron density in the morning, and with clear seasonal and solar activity dependencies. A combined effect of geomagnetic declination and changing zonal winds was proposed to explain it. This paper represents a comprehensive investigation of this effect by examining climatology for both electron density longitudinal differences and the nighttime zonal winds in the eastern US. Electron density is from incoherent scatter radar extra‐wide coverage experiments during 1978–2011 over Millstone Hill for which the spatial separation of the data can be up to 50° in longitude. The thermospheric zonal wind is from the on‐site Fabry‐Perot interferometer measurements during 1989–2001. The observed zonal wind climatology is found to be perfectly consistent with the expectation based on the east‐west electron density differences in terms of local time, seasonal, and solar cycle dependencies. The correlation between the zonal wind and the east‐west differential ratio is extremely high with an overall correlation coefficient of 0.93. The observed time delay of ∼3 hours in the response of electron density differences to zonal winds is a marked feature. Thus these results confirm positively the declination‐zonal wind mechanism and provide new insight into longitudinal variations at midlatitudes for other geographic sectors.