摘要:

Short‐term (6 months to 17 years) glaciochemical records have been collected from glacier basins throughout the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled predominantly by the influx of dust from the arid and semi‐arid regions in central Asia. The glaciochemical data suggests that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the southeastern Tibetan Plateau, are the ones most likely to contain longer‐term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long‐range transport of Asi

ISSN:0094-8276    

DOI:10.1029/93GL01682

年代:1993

数据来源: WILEY

摘要:

This paper evaluates the hypothesis that historical CO2levels could have been governed by releases of geologic methane. Methane clathrates and natural gas could have contributed to CO2increases at the ends of the last two glacial periods. Computations indicate that oxidation of CH4to CO2could have rapidly provided enough CO2to cause historical CO2changes. A simple dynamic model, the hydrocarbon pump, for methane as the source term for changes in CO2over the glacial cycles matches several features of the historical record. If methane clathrates were the source of CO2, then CO2at the interglacial transitions should be depleted in14C because of the low14C levels in C from this source. Evidence is presented that this is the case.13C data are also evaluated. Overall, CH4is a credible source for CO2, but definitive conclusions await further data.

ISSN:0094-8276    

DOI:10.1029/93GL01518

年代:1993

数据来源: WILEY

摘要:

Recent measurements (21 September–15 October 1992) of methane and water vapor by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) are compared with model results for the same season from a troposphere‐middle atmosphere version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM2). Several important features of the two constituent fields are well reproduced by the CCM2, despite the use of simplified methane photochemistry in the CCM2 and some notable differences between the model's zonal mean circulation and climatology. Observed features simulated by the model include the following: 1) subsidence over a deep layer in the Southern Hemisphere polar vortex; 2) widespread dehydration in the polar vortex; 3) existence of a region of low water vapor mixing ratios extending from the Antarctic into the Northern Hemisphere tropics, which suggests that Antarctic dehydration contributes to midlatitude and tropical dryness in the stratosph

ISSN:0094-8276    

DOI:10.1029/93GL01764

年代:1993

数据来源: WILEY

摘要:

The Cl2‐sensitized continuous photolysis of O3mixtures in O2was investigated at 298 K using time resolved single wavelength and diode array spectroscopy to monitor the decay of O3and the formation of OClO. Φ−O3was found to be 4.1±0.4. This value, combined with the determination of the initial rates of OClO formation, allowed the evaluation of the following branching ratios into the three bimolecular disproportionation channels of ClO reactions; k3a/k3= 0.40 ± 0.08, k3b/k3= 0.42 ± 0.08 and k3c/k3= 0.18 ± 0.02 where ClO + ClO → Cl2+ O2(3a), ClO + ClO → Cl + Cl + O2(3b) and ClO + ClO →

ISSN:0094-8276    

DOI:10.1029/93GL01383

年代:1993

数据来源: WILEY

摘要:

A periodicity was observed to drive the 1992 late winter formation of stratospheric clouds over McMurdo Station, Antarctica. Lidar and meteorological data show that intense stratospheric coolings, accompanied by generation of clouds, resulted from the transit of air parcels proceeding from latitudes near the edge of the polar vortex. Lidar depolarization measurements show that large cloud particles could survive for several days in undersaturated air. In the occurrence of further coolings, these particles would act as preferential growth nuclei. Depolarization measurements also indicate that most of the late winter inner vortex sulfuric acid aerosol was frozen. Periodically observed transit of vortex airmasses outside the terminator could be the cause of the wintertime ozone losses, occasionally observed at the very center of the continent.

ISSN:0094-8276    

DOI:10.1029/93GL01385

年代:1993

数据来源: WILEY

摘要:

From uptake measurements of NO2on solid amorphous carbon in the mTorr pressure range and at ambient temperature an accommodation coefficient for NO2of (4.8±0.6)·10−2has been measured. These experiments reveal a complex chemical mechanism. The only major product observed is NO whose yield corresponds to about 60% of the NO2adsorbed on the surface. Thermal desorption of a carbon sample that has been exposed to NO2yields CO and CO2along with some NO3and/or N2O5. H2O does not interact measurably at ambient temperature with the type of carbon used in the present st

ISSN:0094-8276    

DOI:10.1029/93GL01434

年代:1993

数据来源: WILEY

摘要:

Vertical profiles of aerosol have been measured approximately biweekly since June 1991 at Laramie, Wyoming (41°N). Both the total number concentration and concentration of particles>0.15 to 10.0 µm were measured using balloonborne instruments. The aerosol size distributions were best represented when bimodal lognormal distributions were fit to the data. After an early short‐lived intense aerosol layer, the stratospheric maximum surface area and mass (40 µm² cm−3, 160 ppbm) was observed to occur approximately 180 days after the eruption. The aerosol was then observed to remain relatively homogeneous both in altitude and time during 1992, with the maximum surface area and mass remaining relatively constant between 20 to 30 µm² cm−3and 30

ISSN:0094-8276    

DOI:10.1029/93GL01337

年代:1993

数据来源: WILEY

摘要:

The rate at which molecular oxygen absorbs radiation in the O2(X3Σg→b1Σg) transition is calculated using a line‐by‐line radiative transfer model. This rate is critical to the determination of the population of the O2(b1Σg) state required for studies of the O2(b1Σg→X3Σg) dayglow, the O2(a1Δg→X3Σg) dayglow, and possibly the rates of oxidation of H2and N2O. Previous evaluations of this rate (which is sometimes called the g‐factor) have significantly overestimated its value. The rate is tabulated as a function of altitude, pressure, and

ISSN:0094-8276    

DOI:10.1029/93GL01457

年代:1993

数据来源: WILEY

摘要:

The first observations of mean winds and the amplitude and phases of the tidal components measured with a meteor wind radar located at Trivandrum (8.5°N, 77°E) during five consecutive days of counter electrojet events identified in the horizontal component of the earth's magnetic field from January 27–31, 1987 are described. The mean zonal winds in the altitude region of 90–105 km are in general westward during counter electrojet days and eastward during no counter electrojet days. The amplitudes and phases of the tidal components on the counter electrojet days are found to be substantially different from those on the no counter electrojet

ISSN:0094-8276    

DOI:10.1029/93GL00088

年代:1993

数据来源: WILEY

摘要:

Narrow band emissions at frequencies near twice and three times the ionospheric electron cyclotron frequency have been observed with a ground based receiver located at Two Rivers, Alaska (near Fairbanks). The emissions at twice the local ionospheric electron cyclotron frequency ( ≈ 2.50–2.80 MHz) appear similar in frequency, intensity, local time dependence, and temporal structure to auroral “roar” events previously observed at Churchill, Manitoba [Kellogg and Monson, 1979; 1984]. The observation of emissions near 3fce( ≈ 3.66–4.24 MHz), sometimes observed simultaneously with the 2fceevents, represents a new aspect of this phenomenon. A quantitative theoretical understanding of the phenomenon has not yet be

ISSN:0094-8276    

DOI:10.1029/GL020i014p01447

年代:1993

数据来源: WILEY