Bright X-Ray Flares from the BL Lac Object Markarian 421, Detected with MAXI in 2010 January and February

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Strong X-ray flares from the blazar Mrk 421 were detected in 2010 January and February through 7-month monitoring with the MAXI GSC. The maximum 2–10 keV flux in the January and February flares was measured to be 120 ± 10 mCrab and 164 ± 17 mCrab, respectively; the latter is the highest among those reported from the object. A comparison of the MAXI and Swift BAT data suggests a convex X-ray spectrum with an approximated photon index of Γ ≳ 2. This spectrum is consistent with a picture that MAXI is observing near the synchrotron peak frequency. The source exhibited a spectral variation during these flares, slightly different from those in previous observations, in which the positive correlation between the flux and hardness was widely reported. By equating the halving decay timescale in the January flare, tmd ∼ 2.5 × 104 s, to the synchrotron cooling time, the magnetic field was evaluated to be B ∼ 4.5 × 10−2 G (δ/10)−1/3, where δ is the jet beaming factor. Assuming that the light crossing time of the emission region is shorter than the doubling rise time, tmr ≲ 2 × 104 s, the region size was roughly estimated as R < 6 × 1015 cm (δ/10). These results are consistent with values previously reported. For the February flare, the rise time, tmr < 1.3 × 105 s, gives a loose upper limit on the size as R < 4 × 1016 cm (δ/10), although the longer decay time, tmd ∼ 1.4 × 105 s, indicates B ∼ 1.5 × 10−2 G (δ/10)−1/3, which is weaker than the previous results. This could be reconciled by invoking a scenario that this flare is a superposition of unresolved events with a shorter timescale.

Related URLs:
http://pasj.oxfordjournals.org/content/62/6/L55.abstract

Swift Follow-up Observations of MAXI Discovered Galactic Transients

by on 9 June 2015in Earth Science and Remote Sensing No comment

We describe the results of the first year of a program to localize new Galactic Transient sources discovered by MAXI with NASA's Swift mission. Swift is ideally suited for follow-up of MAXI discovered transients as its X-ray Telescope (XRT) field of view (~0.2 degrees radius) is closely matched to the typical MAXI error circle. The XRT is capable of localizing new sources to an accuracy of up to 1.5 arc-seconds radius (90% confidence), and the Swift Optical/UV Telescope also provides optical imaging of any optical counterpart of the X-ray source. If no optical counterpart is found with Swift (usually due to absorption), the XRT position is good enough to allow for ground based IR telescopes to positively identify the optical counterpart. Although localization and identification of MAXI transients is the main aim of the program, these are often followed up by long term monitoring of the source. We present here results from 2 of these monitoring programs: the black-hole candidate MAXI J1659-152, and the Be/X-ray binary candidate MAXI J1409-619.

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Patterns in Crew-Initiated Photography of Earth From ISS — Is Earth Observation a Salutogenic Experience?

by on 9 June 2015in Earth Science and Remote Sensing No comment

Background: To provide for the well-being of crewmembers on future exploration missions, understanding how space station crewmembers handle the inherently stressful isolation and confinement during long-duration missions is important. A recent retrospective survey of previously flown astronauts found that the most commonly reported psychologically enriching aspects of spaceflight had to do with their “Perceptions of Earth.” Crewmembers onboard the International Space Station (ISS) photograph Earth through the station windows. Some of these photographs are in response to requests from scientists on the ground through the Crew Earth Observations (CEO) payload. Other photographs taken by crewmembers have not been in response to these formal requests. The automatically recorded data from the camera provides a dataset that can be used to test hypotheses about factors correlated with self-initiated crewmember photography. The present study used objective in-flight data to corroborate the previous questionnaire finding and to further investigate the nature of voluntary Earth-Observation activity. Methods: We examined the distribution of photographs with respect to time, crew, and subject matter. We also determined whether the frequency fluctuated in conjunction with major mission events such as vehicle dockings, and extra-vehicular activities (EVAs, or spacewalks), relative to the norm for the relevant crew. We also examined the influence of geographic and temporal patterns on frequency of Earth photography activities. We tested the hypotheses that there would be peak photography intensity over locations of personal interest, and on weekends. Results: From December 2001 through October 2005 (Expeditions 4-11) crewmembers took 144,180 photographs of Earth with time and date automatically recorded by the camera. Of the time-stamped photographs, 84.5% were crew-initiated, and not in response to CEO requests. Preliminary analysis indicated some phasing in patterns of photography during the course of a mission (significant quadratic and trimodal models). There was also a small but significant increase in photo activity on the weekends. In contrast, fewer photos were taken during major station events and for a period of time immediately preceding those events. Discussion: Data on photography patterns presented here represent a relatively objective group-level measure of Earth observing activities on ISS. Crew Earth Observations offers a self-initiated positive activity that may be important in salutogenesis (maintenance of well-being) of astronauts on long-duration missions. Consideration should be given to developing substitute activities for crewmembers in future exploration missions where there will not be the opportunity to look at Earth, such as on long-duration transits to Mars.

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Color pictures of sprites from non-dedicated observation on board the International Space Station

by on 9 June 2015in Earth Science and Remote Sensing No comment

Very recently NASA astronauts took a new set of pictures from the International Space Station during night time in the frame of the NASA Crew Earth Observations program, giving a new opportunity to observe in color sprites and their parent lightning flashes. During about 20 h of observations, nondirectly dedicated to thunderstorm studies, 15 sprites were observed from August 2011 to April 2012. Chromatic observations allow analyzing thoroughly the main components of the sprite radiation. The red and green emissions, observed in all the sprite images, are due to the radiation of the first positive band system of molecular nitrogen N2. The blue emission, present in only 2 out of 15 sprites, is produced by the radiation of bands of the second positive band system of N2 and bands of the first negative band system of N2+ ions. It indicates the possible presence of ionization in these two sprites. The sprite brightness is equivalent to the Jupiter one.

Related URLs:
http://dx.doi.org/10.1029/2012JA018144

Evaluating the Diurnal Cycle of Upper-Tropospheric Ice Clouds in Climate Models Using SMILES Observations

by on 9 June 2015in Earth Science and Remote Sensing No comment

Upper-tropospheric ice cloud measurements from the Superconducting Submillimeter Limb Emission Sounder (SMILES) on the International Space Station (ISS) are used to study the diurnal cycle of upper-tropospheric ice cloud in the tropics and midlatitudes (40°S?40°N) and to quantitatively evaluate ice cloud diurnal variability simulated by 10 climate models. Over land, the SMILES-observed diurnal cycle has a maximum around 1800 local solar time (LST), while the model-simulated diurnal cycles have phases differing from the observed cycle by ?4 to 12 h. Over ocean, the observations show much smaller diurnal cycle amplitudes than over land with a peak at 1200 LST, while the modeled diurnal cycle phases are widely distributed throughout the 24-h period. Most models show smaller diurnal cycle amplitudes over ocean than over land, which is in agreement with the observations. However, there is a large spread of modeled diurnal cycle amplitudes ranging from 20% to more than 300% of the observed over both land and ocean. Empirical orthogonal function (EOF) analysis on the observed and model-simulated variations of ice clouds finds that the first EOF modes over land from both observation and model simulations explain more than 70% of the ice cloud diurnal variations and they have similar spatial and temporal patterns. Over ocean, the first EOF from observation explains 26.4% of the variance, while the first EOF from most models explains more than 70%. The modeled spatial and temporal patterns of the leading EOFs over ocean show large differences from observations, indicating that the physical mechanisms governing the diurnal cycle of oceanic ice clouds are more complicated and not well simulated by the current climate models.

Related URLs:
http://dx.doi.org/10.1175/JAS-D-14-0124.1
http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-14-0124.1

River behavior on megafans and potential influences on diversification and distribution of aquatic organisms

by on 9 June 2015in Earth Science and Remote Sensing No comment

Megafans are partial cones of river sediment usually laid down by a single switching river, characterized by areas on the order of 103–105 km2, smooth plains, and slopes of <1°. Astronaut handheld imagery acquired since the early 1980s has permitted the first global geomorphic survey of megafans. Using examples mainly from South America, and based on stream behaviors common in megafans, seven models that appear to have implications for the distribution and diversification of aquatic organisms are presented. River behaviors that appear significant for the fragmentation and age of aquatic habitats on megafans include river switching (models 1.1–1.4) and the disconnection of the megafan river from the main river of the basin (models 2–4). Each model has a habitat fragmentation and a habitat combining mode. In their vicariant mode, models 1.1 and 1.2 involve longer periods of time. Models 1.3 and 1.4 involve the relatively instantaneous merging of aquatic populations from neighboring megafan rivers or neighboring major basins. Models 2–4 involve longer-term dynamics with the potential for speciation. We identify the following levels of diversity related to scales of stream operation: intrafan diversity, or local populations and among local populations; interfan diversity, or among local populations and species; and interbasin diversity, or species and biotas.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0895981105001409

Remote sensing of selected water-quality indicators with the hyperspectral imager for the coastal ocean (HICO) sensor

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The Hyperspectral Imager for the Coastal Ocean (HICO) offers the coastal environmental monitoring community an unprecedented opportunity to observe changes in coastal and estuarine water quality across a range of spatial scales not feasible with traditional field-based monitoring or existing ocean colour satellites. HICO, an Office of Naval Research-sponsored programme, is the first space-based maritime hyperspectral imaging instrument designed specifically for the coastal ocean. HICO has been operating since September 2009 from the Japanese Experiment Module – Exposed Facility on the International Space Station (ISS). The high pixel resolution (approximately 95 m at nadir) and hyperspectral imaging capability offer a unique opportunity for characterizing a wide range of water colour constituents that could be used to assess environmental condition. In this study, we transform atmospherically corrected ISS/HICO hyperspectral imagery and derive environmental response variables routinely used for evaluating the environmental condition of coastal ecosystem resources. Using atmospherically corrected HICO imagery and a comprehensive field validation programme, three regionally specific algorithms were developed to estimate basic water-quality properties traditionally measured by monitoring agencies. Results indicated that a three-band chlorophyll a algorithm performed best (R2 = 0.62) when compared with in situ measurement data collected 2–4 hours of HICO acquisitions. Coloured dissolved organic matter (CDOM) (R2 = 0.93) and turbidity (R2 = 0.67) were also highly correlated. The distributions of these water-quality indicators were mapped for four estuaries along the northwest coast of Florida from April 2010 to May 2012. However, before the HICO sensor can be transitioned from proof-of-concept to operational status and its data applied to benefit decisions made by coastal managers, problems with vicarious calibration of the sensor need to be resolved and standardized protocols are required for atmospheric correction. Ideally, the sensor should be placed on a polar orbiting platform for greater spatial and temporal coverage as well as for image synchronization with field validation efforts.

Related URLs:
http://dx.doi.org/10.1080/01431161.2014.894663
http://www.tandfonline.com/doi/abs/10.1080/01431161.2014.894663

Spatial distribution patterns of chlorophyll-a and suspended matter in the Yangtze Estuary and the Hangzhou Bay as observed with the Hyperspectral Imager for the Coastal Ocean (HICO)

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Data from the Hyperspectral Imager for the Coastal Ocean (HICO) were used to identify gradients and patchiness due to chl-a and suspended matter in the Yangtze Estuary and the Hangzhou Bay in China. HICO images were classified using the spectral analysis to identify frontal systems and areas of plankton patchiness in these water bodies. The results obtained from the analysis were compared with results obtained from previous studies conducted in these water bodies. The chl-a concentrations estimated from atmospherically corrected HICO images were comparable to chl-a concentrations measured in situ previously in this region. The spatial patterns of chl-a distribution derived from the HICO data matched well with the spatial patterns derived from a MODIS image acquired on the same day.

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Diurnal variation of stratospheric and lower mesospheric HOCl, ClO and HO2 at the equator: comparison of 1-D model calculations with measurements by satellite instruments

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The diurnal variation of HOCl and the related species ClO, HO2 and HCl measured by satellites has been compared with the results of a one-dimensional photochemical model. The study compares the data from various limb-viewing instruments with model simulations from the middle stratosphere to the lower mesosphere. Data from three sub-millimetre instruments and two infrared spectrometers are used, namely from the Sub-Millimetre Radiometer (SMR) on board Odin, the Microwave Limb Sounder (MLS) on board Aura, the Superconducting Submillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satellites (SMR, MLS, MIPAS) and measurements from solar occultation instruments (ACE-FTS) is challenging since the measurements correspond to different solar zenith angles (or local times). However, using a model which covers all solar zenith angles and data from the SMILES instrument which measured at all local times over a period of several months provides the possibility to verify the model and to indirectly compare the diurnally variable species. The satellite data were averaged for latitudes of 20° S to 20° N for the SMILES observation period from November 2009 to April 2010 and were compared at three altitudes: 35, 45 and 55 km. Besides presenting the SMILES data, the study also shows a first comparison of the latest MLS data (version 3.3) of HOCl, ClO, and HO2 with other satellite observations, as well as a first evaluation of HO2 observations made by Odin/SMR. The MISU-1D model has been carefully initialised and run for conditions and locations of the observations. The diurnal cycle features for the species investigated here are generally well reproduced by the model. The satellite observations and the model agree well in terms of absolute mixing ratios. The differences between the day and night values of the model are in good agreement with the observations although the amplitude of the HO2 diurnal variation is 10–20% lower in the model than in the observations. In particular, the data offered the opportunity to study the reaction ClO+HO2 → HOCl+O2 in the lower mesosphere at 55 km. At this altitude the HOCl night-time variation depends only on this reaction. The result of this analysis points towards a value of the rate constant within the range of the JPL 2006 recommendation and the upper uncertainty limit of the JPL 2011 recommendation at 55 km.

Related URLs:
http://www.atmos-chem-phys.net/13/7587/2013/
http://www.atmos-chem-phys.net/13/7587/2013/acp-13-7587-2013.pdf