Technical Note: Measurement of the tropical UTLS composition in presence of clouds using millimetre-wave heterodyne spectroscopy

The MARSCHALS (Millimetre-wave Airborne Receiver for Spectroscopic CHaracterisation of Atmospheric Limb-Sounding) project has the general objectives of demonstrating the measurement capabilities of a limb viewing instrument working in the millimetre and sub-millimetre spectral regions (from 294 to 349 GHz) for the study of the Upper Troposphere – Lower Stratosphere (UTLS). MARSCHALS has flown on board the M-55 stratospheric aircraft (Geophysica) in two measurements campaigns. Here we report the results of the analysis of MARSCHALS measurements during the SCOUT-O3 campaign held in Darwin (Australia) in December 2005 obtained with MARC (Millimetrewave Atmospheric-Retrieval Code). MARSCHALS measured vertical distributions of temperature, water vapour, ozone and nitric acid in the altitude range from 10 to 20 km in presence of clouds that obscure measurements in the middle infrared spectroscopic region. The minimum altitude at which the retrieval has been possible is determined by the high water concentration typical of the tropical region rather than the extensive cloud coverage experienced during the flight. Water has been measured from 10 km to flight altitude (~18 km) with a 10% accuracy, ozone from 14 km to flight altitude with accuracy ranging from 10% to 60%, while the retrieval of nitric acid has been possible with an accuracy not better than 40% only from 16 km to flight altitude due to the low signal to noise ratio of its emission in the analysed spectral region. The results have been validated using measurement made in a less cloudy region by MIPAS-STR, an infrared limb-viewing instrument on board the M-55, during the same flight

Tonotopic organization of the insect auditory pathway

The tonotopic organization of the Orthopteran auditory pathway is but one example of topographic representation in nervous systems. However, it may prove a prime model for understanding the creation of more complex neuronal architecture. The pathway is extremely simple, containing as few as 20 receptors, each individually tuned to a specific sound frequency, and a small number of interneurons. Physiological recordings can be made from each element in the pathway and from individuals at various stages of neural development. This review describes the tonotopic organization of the auditory organs and primary auditory neuropiles of Orthopterans, and discusses the significance of this organization for auditory processing

Physiology of auditory receptors in two species of Tettigoniidae (Orthoptera: Ensifera)

1. The gross anatomical features of the crista acustica in the tettigoniids Mygalopsis marki and Polichne sp. are compared (Fig. 1). The crista in Polichne sp. was longer and contained 12 more receptors than that in M. marki. Both organs, however, displayed a gradual and even taper from the proximal to the distal end. The size of the attachment cells and the length of the sensory dendrites displayed a similar gradual decrease in size from the proximal to the distal end of the array (Fig. 1). 2. The characeristic sound frequency and roll offs in sensitivity of ascending auditory interneurons in the oesophageal connectives of M. marki did not alter after the leg cuticle covering the crista acustica was removed (Fig. 2). Since such interneurons receive excitatory and possible inhibitory input from several receptors in the crista this result indicated that the tuning of these receptors was not affected by removing this portion of the leg cuticle. 3. Physiological recordings were obtained from the cell bodies of individual receptors in the crista acustica of M. marki and Polichne sp. (Fig. 3 A, B). Receptors in M. marki produced a maximum response to an 80 ms tone pulse of 16 spikes/stimulus, had a dynamic range of approximately 30 dB and a rate of increase in the spike response of 6 spikes/10 dB (Fig. 3C). The maximum response, dynamic range and slope of the intensity-response characteristics of auditory receptors in Polichne sp. were less than that for receptors in M. marki (Fig. 3 D). The slope of the intensity response characteristics, dynamic range and maximum spike response of individual auditory receptors in both M. marki and Polichne sp. did not alter for sound frequencies above and below the characteristic frequency of the individual receptor (Fig. 3 C, D). 4. The tonotopic organisation of the crista acustica in M. marki and Polichne sp. was determined by the injection of Lucifer Yellow into the cell bodies and dendrites (Fig. 4 A) of receptors for which the frequency-threshold characteristics had been obtained (Fig. 4B). The characteristic frequencies of adjacent receptors in the crista acustica of M. marki were seperated by irregular amounts with receptor 6 tuned to 7 kHz, receptor 7 to 14 kHz, receptor 8 to 17 kHz and receptors 10 and 11 tuned to 20 kHz (Fig. 6). Although adjacent receptors in Polichne sp. were seperated by approximately 1 kHz, the crista acustica of the species contains four receptors tuned to 20 kHz (Fig. 7). 5. The discontinuities in the tonotopic organisation of the crista acustica of M. marki and Polichne sp. are incompatable with the notion that mechanical resonances within the receptor array could be responsible for the frequency selectivity of these auditory receptors. It is therefore proposed that these receptors are tuned as a result of electrical and/or mechanical resonance intrinsic to the individual sensilla

The tuning of auditory receptors in bushcrickets

The auditory organ of bushcrickets consists of an array of chordotonal sensilla in the insect's foreleg. Physiological recordings from these sensilla demonstrate that the individual receptors are tuned to specific sound frequencies and that the array is tonotopically organised. This frequency selectivity and tonotopic organisation are not altered by severely disrupting the integrity of the receptor array. Since the tuning of the individual receptors is not dependent on resonance in the auditory canal (prothoracic trachea), tympanal membranes or receptor array it is proposed that it is due to mechanical and/or electrical properties of the individual receptors

Tonotopic organisation of the auditory organ of the locust Valanga irregularis (Walker)

The responses to pure tone stimuli of individual auditory receptors in the locust Valanga irregularis were quantified and the location of receptors within the auditory organ identified through the intracellular injection of Lucifer Yellow. Three groups of receptors were identified and classified according to their site of attachment to the tympanic membrane (Gray 1960). Group 'a' cells were attached to the elevated process and were tuned to sound frequencies from 4 to 6 kHz (Fig. 2). Group 'c' cells were attached to the folded body and were tuned to sound frequencies from 2 to 3.5 kHz (Fig. 3). Group 'd' cells were attached to the pyriform vesicle and were tuned to sound frequencies from 14 to 25 kHz (Fig. 4). The receptor cell bodies belonging to these groups were separated into three distinct regions of the auditory organ (Fig. 5). There was no evidence of any tonotopic organisation within the three groups (Fig. 6). These data therefore support the conclusion that the receptors within the auditory organ of the locust are organized into specific physiological groups (Michelsen 1971a) and thus suggest that the mechanics of the auditory apparatus may indeed play a role in defining the tuning of the receptors