Kj Michael

Foraging strategies of southern elephant seals ( Mirounga leonina ) in relation to frontal zones and water masses

Geolocating-time-depth-temperature-recorders (GLTDTR) provided a continuous record of diving behaviour in relation to water temperature for ten female southern elephant seals from Macquarie Island during their post-breeding trips to sea. Four water bodies were determined from depth/temperature profiles recorded by the GLTDTRs. These water bodies corresponded to Sub-Antarctic Mode Water (SAMW), Polar Front Zone Water (PFZW), Polar Front Water (PFW) and Antarctic Water Masses (AWM). Thermal structures within these water bodies did not influence seal diving behaviour. Overall mean dive depth, nocturnal dive depths, diurnal dive depths and dive duration were similar in all areas. However, individuals did change behaviour as they moved between different water bodies. Seals also used different water bodies in the two different years of the study. We suggest that variations in foraging behaviour among seals are a result of prey distribution associated with local oceanographic conditions, but also reflect important individual foraging strategies within thermal zones.

East Antarctic Landfast Sea Ice Distribution and Variability, 2000–08

AbstractThis study presents the first continuous, high spatiotemporal resolution time series of landfast sea ice extent along the East Antarctic coast for the period March 2000–December 2008. The time series was derived from consecutive 20-day cloud-free Moderate Resolution Imaging Spectroradiometer (MODIS) composite images. Fast ice extent across the East Antarctic coast shows a statistically significant (1.43% ±0.30% yr−1) increase. Regionally, there is a strong increase in the Indian Ocean sector (20°–90°E, 4.07% ±0.42% yr−1), and a nonsignificant decrease in the western Pacific Ocean sector (90°–160°E, −0.40% ±0.37% yr−1). An apparent shift from a negative to a positive extent trend is observed in the Indian Ocean sector from 2004. This shift also coincides with a greater amount of interannual variability. No such shift in apparent trend is observed in the western Pacific Ocean sector, where fast ice extent is typically higher and variability lower than the Indian Ocean sector. The limit to the maximu...

An Improved Model for Relativistic Solar Proton Acceleration Applied to the 2005 January 20 and Earlier Events

This paper presents results on modeling the ground-level response of the higher energy protons for the 2005 January 20 ground-level enhancement (GLE). This event, known as GLE 69, produced the highest intensity of relativistic solar particles since the famous event on 1956 February 23. The location of recent X-ray and γ-ray emission (N14° W61°) was near Sun-Earth connecting magnetic field lines, thus providing the opportunity to directly observe the acceleration source from Earth. We restrict our analysis to protons of energy ≥450 MeV to avoid complications arising from transport processes that can affect the propagation of low-energy protons. In light of this revised approach we have reinvestigated two previous GLEs: those of 2000 July 14 (GLE 59) and 2001 April 15 (GLE 60). Within the limitations of the spectral forms employed, we find that from the peak (06:55 UT) to the decline (07:30 UT) phases of GLE 69, neutron monitor observations from 450 MeV to 10 GeV are best fitted by the Gallegos-Cruz & Perez-Peraza stochastic acceleration model. In contrast, the Ellison & Ramaty spectra did not fit the neutron monitor observations as well. This result suggests that for GLE 69, a stochastic process cannot be discounted as a mechanism for relativistic particle acceleration, particularly during the initial stages of this solar event. For GLE 59 we find evidence that more than one acceleration mechanism was present, consistent with both shock and stochastic acceleration processes dominating at different times of the event. For GLE 60 we find that Ellison & Ramaty spectra better represent the neutron monitor observations compared to stochastic acceleration spectra. The results for GLEs 59 and 60 are in agreement with our previous work.

Measurements of erythemal irradiance near Davis Station, Antarctica: Effect of inhomogeneous surface albedo

To examine effects of inhomogeneous surface albedo on UV irradiance, measurements were taken near Davis Station (68.58°S, 77.97°E), East Antarctica during November/December 1997. Data were collected in transects perpendicular to an ice/water boundary, while one instrument continuously measured at the ice edge. Irradiances along transects were normalised by coincident measurements at the ice edge. Systematic differences in downwelling irradiance near the ice edge were observed over the highly reflective surface and open water. For cloudless conditions, the relative change in irradiance reached limiting values of about +5% from the ice edge to a point 2.5 km over snow-covered ice, and about −5% from the ice edge to a point 2.5 km over water. In overcast conditions, higher relative changes were observed (about +30% from the ice edge to a point 2.5 km over ice on 17 November 1997) with no sign of a constant relative change being reached.

The influence of polar-cap convection on the geoelectric field at Vostok, Antarctica

Abstract Vertical geoelectric field measurements at Vostok, Antarctica ( 78.5° S , 107° E ; corrected geomagnetic latitude, 83.4°S) made during 1998 are compared with both Weimer (1996) and IZMEM (1994) model calculations of the solar-wind-induced, polar-cap potential differences with respect to the station. By investigating the correlations between these parameters for individual UT hours, we confirm and extend the diurnal range over which significant correlations have been obtained. Nineteen individual UT hours are significantly correlated with the Weimer model predictions and nine with the IZMEM model predictions. Diurnal variation in the slopes of the linear regressions allows us to comment on each model, demonstrating that Antarctic polar plateau geoelectric field measurements can be used to investigate polar convection. Seasonal variations in the diurnal electric field variations at Vostok are compared with the Carnegie global electric circuit diurnal curves, after allowance is made for the solar-wind-induced, polar-cap potential difference patterns.

Relativistic Proton Production during the 2000 July 14 Solar Event: The Case for Multiple Source Mechanisms

Protons accelerated to relativistic energies by transient solar and interplanetary phenomena caused a ground-level cosmic-ray enhancement on 2000 July 14, Bastille Day. Near-Earth spacecraft measured the proton flux directly, and ground-based observatories measured the secondary responses to higher energy protons. We have modeled the arrival of these relativistic protons at Earth using a technique that deduces the spectrum, arrival direction, and anisotropy of the high-energy protons that produce increased responses in neutron monitors. To investigate the acceleration processes involved we have employed theoretical shock and stochastic acceleration spectral forms in our fits to spacecraft and neutron monitor data. During the rising phase of the event (10:45 and 10:50 UT) we find that the spectrum between 140 MeV and 4 GeV is best fitted by a shock acceleration spectrum. In contrast, the spectrum at the peak (10:55 and 11:00 UT) and in the declining phase (11:40 UT) is best fitted with a stochastic acceleration spectrum. We propose that at least two acceleration processes were responsible for the production of relativistic protons during the Bastille Day solar event: (1) protons were accelerated to relativistic energies by a shock, presumably a coronal mass ejection (CME); and (2) protons were also accelerated to relativistic energies by stochastic processes initiated by magnetohydrodynamic (MHD) turbulence.

Remote sensing of Southern Ocean sea surface temperature: implications for marine biophysical models

Nineteen years of Advanced Very High Resolution Radiometer Multi-Channel Sea Surface Temperature (AVHRR MCSST) data were used to calculate monthly averages of sea surface temperatures (SSTs) for a large region of the Southern Ocean centred on Macquarie Island. Between October and February, the MCSST data were a reliable source of SSTs north of 60°S, but their quality (i.e. spatial and temporal density) was degraded severely at higher latitudes. Between April and August, the interpolated MCSST data were found to be unreliable in the study area, even at latitudes as low as 45°S. A specific problem has been identified to the west of Tasmania in the winter interpolated climatology which is likely an artefact of interpolation of sparse data. The poor coverage of valid MCSSTs during this time limits the datas application for many uses. Although the limitations of the MCSST data set are well recognised, the possibilities for ecological applications of these data remain largely unexplored and unquantified. The potential exists to maximize the information available from this and other similar data sets by determining the appropriate spatial and temporal scales at which they are best applied to biophysical models.

Relativistic Proton Production during the 2001 April 15 Solar Event

Extreme solar processes at the Sun on 2001 April 15 accelerated protons to relativistic energies, resulting in a ground-level enhancement in cosmic rays observed at Earth. The GOES 10 spacecraft measured the proton flux directly, and ground-based observatories measured the secondary responses to higher energy protons. We have modeled the ground-level response to this event using a technique that deduces the spectrum, arrival direction, and anisotropy of the high-energy protons. To investigate the acceleration process(es), we have employed theoretical shock and stochastic acceleration spectral forms in our fits to spacecraft and neutron-monitor data. In the case of stochastic acceleration, we use two different spectral forms. The first (model A) incorporates an idealized preacceleration step through monoenergetic injection. The second (model B) incorporates a more realistic injection function using preacceleration by DC electric fields in a reconnecting neutral current sheet. We find that at the rise, peak, and decline phases of the event (14:20, 14:30, and 14:45 UT, respectively), the spectrum between 120 MeV and 10 GeV is best fitted by a shock acceleration spectral form. This implies that protons were accelerated to relativistic energies either by a coronal shock or at the bow shock of the 2001 April 15 coronal mass ejection. In addition, reinvestigation of the 2000 July 14 solar event using the more realistic injection function (model B) further supports our earlier findings that MHD turbulence arising from magnetic reconnection from a dissipating neutral current sheet was important in relativistic proton production for that event.

Shallow-water wave lensing in coral reefs: a physical and biological case study.

SUMMARY Wave lensing produces the highest level of transient solar irradiances found in nature, ranging in intensity over several orders of magnitude in just a few tens of milliseconds. Shallow coral reefs can be exposed to wave lensing during light-wind, clear-sky conditions, which have been implicated as a secondary cause of mass coral bleaching through light stress. Management strategies to protect small areas of high-value reef from wave-lensed light stress were tested using seawater irrigation sprinklers to negate wave lensing by breaking up the water surface. A series of field and tank experiments investigated the physical and photophysiological response of the shallow-water species Stylophora pistillata and Favites abdita to wave lensing and sprinkler conditions. Results show that the sprinkler treatment only slightly reduces the total downwelling photosynthetically active and ultraviolet irradiance (∼5.0%), whereas it dramatically reduces, by 460%, the irradiance variability caused by wave lensing. Despite this large reduction in variability and modest reduction in downwelling irradiance, there was no detectable difference in photophysiological response of the corals between control and sprinkler treatments under two thermal regimes of ambient (27°C) and heated treatment (31°C). This study suggests that shallow-water coral species are not negatively affected by the strong flashes that occur under wave-lensing conditions.

A Method for Compositing Polar MODIS Satellite Images to Remove Cloud Cover for Landfast Sea-Ice Detection

This paper presents details of techniques for generating thermal infrared and visible composite images from the cloud-free portions of temporally closely spaced MODerate resolution Imaging Spectroradiometer (MODIS) images, with a focus on studies of landfast sea ice along the East Antarctic coast. Composite image inclusion criteria are based on modified MODIS Earth Observing System cloud mask product results. The compositing process presented places emphasis on retaining maximum spatial resolution while minimizing storage space requirements. Composite images can be produced either as a regular product (e.g., on a ten-day grid), or dynamically (whenever enough information is acquired to produce a new output image). The techniques presented are applicable at any latitude, are available for all MODIS channels at their native resolution, can combine Aqua and Terra images, and can produce maps in any output projection. However, due to the polar orbit of NASAs Terra and Aqua satellites which host the MODIS instrument, more frequent coverage is produced at higher latitudes. Thus, the techniques presented are particularly applicable to polar research. Examples of composite image generation of the landfast sea ice around the Mertz Glacier region, East Antarctica, are included for both winter and summer.