Analysis of Jupiter North Equatorial Belt hot spots in the 4-5 μm range from Galileo/near-infrared mapping spectrometer observations: Measurements of cloud opacity, water, and ammonia

This paper presents the analysis of hot spot observations in the Jovian North Equatorial Belt obtained with the near-infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft. The data were acquired during the closest approach sequences between June 1996 and April 1997. We focus on the spectral window between 4.5 and 5.2 [Jim determining the cloud opacity above 2 bar, the water vapor relative humidity, and the ammonia abundance between 4 and 8 bar. We find a linear relationship between the cloud opacity and the continuum level of the spectrum. For a given radiance level of an individual spectrum, significant variations in the water vapor relative humidity are seen. However, no clear evidence for a relationship between the cloud opacity and the water relative humidity is seen. A cloud structure similar to that measured by the Galileo entry probe, with no significant cloud opacity below 2 bar, is adequate. The air in the hot spots is found to be overall dry, consistent with the probe measurements. None of the considered spectra show water vapor relative humidities exceeding 10%. Significant spatial variations of the water vapor relative humidity are found, and the distribution over the observed hot spot regions is complex. Because of a low sensitivity of the NIMS spectra to ammonia, uncertainties in the derived ammonia abundance are much higher than for water. There is, however, a possible trend in all the observed hot spots toward more ammonia inside than outside the hot spots at the sounded pressure levels. Copyright 1998 by the American Geophysical Union.