[1] Here we present extensive observations of stratospheric and upper tropospheric water vapor using the balloon-borne Cryogenic Frost point Hygrometer (CFH) in support of the Aura Microwave Limb Sounder (MLS) satellite instrument. Coincident measurements were used for the validation of MLS version 1.5 and for a limited validation of MLS version 2.2 water vapor. The sensitivity of MLS is on average 30% lower than that of CFH, which is fully compensated by a constant offset at stratospheric levels but only partially compensated at tropospheric levels, leading to an upper tropospheric dry bias. The sensitivity of MLS observations may be adjusted using the correlation parameters provided here. For version 1.5 stratospheric observations at pressures of 68 hPa and smaller MLS retrievals and CFH in situ observations agree on average to within 2.3% ± 11.8%. At 100 hPa the agreement is to within 6.4% ± 22% and at upper tropospheric pressures to within 23% ± 37%. In the tropical stratosphere during the boreal winter the agreement is not as good. The ''tape recorder'' amplitude in MLS observations depends on the vertical profile of water vapor mixing ratio and shows a significant interannual variation. The agreement between stratospheric observations by MLS version 2.2 and CFH is comparable to the agreement using MLS version 1.5. The variability in the difference between observations by MLS version 2.2 and CFH at tropospheric levels is significantly reduced, but a tropospheric dry bias and a reduced sensitivity remain in this version. In the validation data set a dry bias at 177.8 hPa of À24.1% ± 16.0% is statistically significant.

The June 1991 eruption of the Philippine volcano Pinatubo introduced a massive plume of volcanic ash and other aerosol material into a stratosphere containing only near‐background concentrations of aerosol material. At Mauna Loa Observatory, Hawaii, the Pinatubo plume was first observed by lidar on 1 July 1991. During July and August the observable effects from this plume increased in intensity in terms of aerosol optical properties, plume height, and broad band solar radiation. Preliminary data analysis shows that the plume over Hawaii arrived in three generalized pulses or waves on approximately 3 July, 24 July, and 9 August. There was a decrease of about 13% in a broad band atmospheric transmission factor over Hawaii between June 1991 and Pinatubo affected conditions on 31 August 1991. At the end of August 1991, the Pinatubo plume over Hawaii exhibited characteristics similar in magnitude to what was observed at Mauna Loa after the El Chichon eruption in 1982. However, the early Pinatubo maximum plume heights were lower than were observed in the early months of the El Chichon plume dispersion. The Pinatubo plume was continuing to increase in magnitude and height at MLO at the end of August.

Abstract. The mountain wind field in the vicinity of Mauna Loa Observatory is derived by comparing vertical profiles of wind, ozone, and water vapor in the free troposphere to measurements made at the observatory. The wind field near the surface is described by two components: a radiation wind caused by the diurnal heating and cooling of the mountain slope, and a barrier wind caused by the free tropospheric wind flowing around the mountain barrier. The radiation wind is the primary factor in transporting air from different source altitudes in the freetroposphere to the observatory at 3400 m. At midday, air typically arrives from near the top of the marine boundary layer at 2500 m. After midnight, the average source altitude is 3400 m. The barrier wind field consists of a windward stagnation point, strong cross-slope and downslope flow in the flanks, and moderate downslope flow in the leeward sectors. The barrier wind field is effective at disrupting the surface temperature inversion and the radiation wind at night. A simple model is presented which relates the average properties and statistical variation of these winds to the vertical transport of air from the free troposphere to the observatory by the mountain wind field.

Thirteen years of continuous atmospheric carbon dioxide and methane measurements at the Mauna Loa Observatory in Hawaii are used to determine the methane emission rate from the summit of Mauna Loa volcano. We find no measurable methane emissions coming from the summit area, with a 95% confidence upper limit of 9 t CH4 yr−1. Recent studies have detected 10 ppb CH4 in the Martian atmosphere, requiring emissions of about 300 t CH4 yr−1. Volcanic activity has been suggested as a source of abiogenic CH4 on Mars, either by magmatic degassing or reactions in hydrothermal fluids heated by a magma intrusion. The most recent lava flows on Mars (2 My ago) are on the Tharsis shield volcanoes, which may still be active. If Mauna Loa is a valid terrestrial analog, our findings suggest that volcanic activity is not a significant source of methane to the Martian atmosphere.

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