Rangasayi N. Halthore

Infrared polar brightenings on Jupiter: IV. Spatial properties of methane emission

Abstract Polar “hot spots” observed on Jupiter at 7.8 μm with the NASA Infrared Telescope Facility at Mauna Kea, Hawaii, reveal different characteristics in the northern and southern hemispheres. The hot spot in the northern hemisphere is found to be fixed with respect to system III coordinates at 180±10° long and 60±10° lat. In contrast, the south polar hot spot is not fixed with respect to system III longitude; neither is it fixed with respect to the subsolar point or to Ios position. Additional analysis of the north polar hot spot, also with the help of Voyager I IRIS data, reveals that it is more extended in longitude than in latitude.

Infrared polar brightenings on Jupiter. V: A thermal equilibrium model for the north polar hot spot

Abstract Infrared hydrocarbon emissions from Jupiters north polar region, recorded using the Voyager IRIS instrument, determine spatial and other properties of the north polar hot spot. Emission at 7.8 μm by stratospheric methane reveals that the peak is asymmetric with respect to system III longitude. A thermal equilibrium model exploits this asymmetry to derive an estimate for the zonal wind velocity in the stratosphere. The same model predicts accurately the observed asymmetry in acetylene emission at 13.6 μm, but requires that the acetylene abundance be enhanced in the hot spot. Ethane, in contrast, appears to be depleted. Energetic charged particles are the most probable cause of these effects; their energies determine the altitude of the hot spot in the stratosphere, estimated here to be between the 1-mbar and 1-μbar pressure levels.

Trace-gas measurements with an infrared sun photometer

Accurate assessment of the potential impact of greenhouse gases and aerosols on the Earth system can be enhanced by a global monitoring network and can be facilitated by the development of compact, portable optical instruments for field use. The more important of these gases, e.g., methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O), have strong absorptions at wavelengths between 2 and 5 micrometers ; however, this spectral region is heavily dominated by absorption by water (H2O) which is itself an important contributor to radiative transfer at these wavelengths. To achieve the desired reduction in instrument size, it is often necessary to relax wavelength resolution requirements which in turn affects the accuracy and precision of the retrieved column abundances. To address these measurement problems, an infrared sun photometer has been constructed for application to trace-gas detection and analysis techniques are being developed to extract column abundances from the spectrally congested data. The current instrument design is based on a circular variable filter (CVF) with wavelength coverage from 1.2 to 5 micrometers . Preliminary measurements with this instrument are presented and electro-optical alternatives to the CVF as the tuning element are discussed.

Simulation of the spectral content of the 7.8-μm emission from Jupiter at high resolution

Abstract Jovian emission due to 12 CH 4 , 13 CH 4 , and CH 3 D in the 1100 to 1400 cm −1 region is simulated at high spectral resolution as seen from the Earth from an altitude of 4 km above sea level. Due to absorption in the Earths atmosphere, strong lines do not contribute significantly to the total intensity in this region; it is the weak to marginally strong lines that contribute most. Polar hot spots and other midlatitude features observed in broadband observations are conclusively shown to be stratospheric effects. Signal enhancement in the broadband observations is obtained at zenith angles close to zero and increased doppler shifts; however, the magnitude in the latter case is a sensitive function of the stratospheric temperature.