With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters. Mesopelagic fishes dominate the global fishes biomass, yet there exist major uncertainties regarding their global biomass. Irigoien et al.analyse acoustic data collected during a circumglobal cruise and show that biomass estimates should be raised by an order of magnitude.

/pdf/large-mesopelagic-fishes-biomass-and-trophic-efficiency-in-1q1fmxkuue.pdf

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

/pdf/the-global-atmospheric-electric-circuit-solar-activity-and-5e4z8tnd4k.pdf

The global atmospheric electric circuit, solar activity and climate change

. An experimental Very Low Frequency (VLF) World-Wide Lightning Location Network (WWLLN) has been developed through collaborations with research institutions across the world, providing global real-time locations of lightning discharges. As of April 2006, the network included 25 stations providing coverage for much of the Earth. In this paper we examine the detection efficiency of the WWLLN by comparing the locations from this network with lightning location data purchased from a commercial lightning location network operating in New Zealand. Our analysis confirms that WWLLN favours high peak current return stroke lightning discharges, and that discharges with larger currents are observed by more stations across the global network. We then construct a first principles detection efficiency model to describe the WWLLN, combining calibration information for each station with theoretical modelling to describe the expected amplitudes of the VLF sferics observed by the network. This detection efficiency model allows the prediction of the global variation in WWLLN lightning detection, and an estimate of the minimum CG return stroke peak current required to trigger the network. There are strong spatial variations across the globe, primarily due to station density and sensitivity. The WWLLN is currently best suited to study the occurrence and impacts of high peak-current lightning. For example, in 2005 about 12% of the global elve-producing lightning will have been located by the network. Since the lightning-EMP which produce elves has a high mean rate (210 per minute) it has the potential to significantly influence the ionosphere on regional scales.

https://angeo.copernicus.org/articles/24/3197/2006/angeo-24-3197-2006.pdf

Detection efficiency of the VLF World-Wide Lightning Location Network (WWLLN): initial case study

Introduction to ionospheric heating at Tromsø—I. Experimental overview

ELF and VLF radio waves

ELF and VLF wave generation by HF heating: A comparison of AM and CW techniques

Using the simple slab-cylinder acoustic model for fish, developed by Clay and Horne [J. Acoust. Soc. Am. 96, 1661–1668 (1994)], the target strengths of three of New Zealand’s deep-water fish species, namely orange roughy, black oreos, and smooth oreos, have been derived. The target strengths derived for the model fish have been found to be in reasonable agreement with currently accepted target strength values. These three model fish were used in a study to test the species discrimination of a chirp sonar system. Chirps of center frequencies 40, 80, and 160 kHz and bandwidth of 10, 20, and 40 kHz have been used to acoustically illuminate the three fish species listed above and the matched, filtered responses to the chirps determined. The effect of the response of transducer or system bandwidth has also been investigated. It has been found that the bandwidth of the chirp is much more important for resolving detail in a fish target than the chirp center frequency. A bandwidth of at least 20 kHz, and preferably 40 kHz, produces matched filtered responses for black and smooth oreos and orange roughy which are quite clearly species specific. Results suggest that with orange roughy it may be possible to size and even sex the targets acoustically.

A design study of an acoustic system suitable for differentiating between orange roughy and other New Zealand deep-water species

Using amplitude modulation derived from repetitive pulses of varying duty cycle with the Tromsoe heater facility, the authors determine the ratio of the heating to cooling time constants of ELF currents generated in the D-region. This ratio is found to decrease from 1.03 {plus minus} 0.07 at 510 Hz to 0.28 {plus minus} 0.03 at 6,010 kHz. These results, which were obtained using an effective radiated power of 240 MW, suggest that future heater facilities designed to optimize ELF radiation efficiency using the technique of beam painting' will have to operate at considerably higher power levels than the Tromsoe facility if any practical advantages are to be gained.

On the ELF generation efficiency of the Tromsø Heater Facility

Using a new experimental technique the response of the auroral ionosphere to a very powerful HF wave amplitude modulated by an ELF square wave has been determined independent of the obfuscating effects of earth-ionosphere-waveguide resonances. It has been found that when resonance effects are compensated for, the odd harmonic amplitude ratios are predominantly those one would expect for a square wave, slightly modified by the non-linear relationship between generated ELF signal and HF radiated power. The even harmonic amplitude ratios are found to be much lower than those observed in earlier experiments and have been modelled by assuming unequal electron heating and cooling time constants and hence different rise and fall times for the ionospheric currents.

Richard Barr

Papers

ELF and VLF radio waves

ELF and VLF wave generation by HF heating: A comparison of AM and CW techniques

A design study of an acoustic system suitable for differentiating between orange roughy and other New Zealand deep-water species

On the ELF generation efficiency of the Tromsø Heater Facility

ELF harmonic radiation from the Tromsø Heating Facility