摘要:

This paper documents a larger degree of mixing in ice near the bottom of an ice sheet than described, or suspected, previously. It shows, thanks to favourable circumstances due to CO2and CH4production underneath the ice, that flow‐induced mixing within the basal ice has taken place at the scale of a few centimeters in the GRIP core. Such a mechanism must be considered when interpreting the ice properties in the bottom part of ice sheets and must be taken into account as a potential process of layer disruption in the low levels of the Central Greenland ice core

ISSN:0094-8276    

DOI:10.1029/94GL02863

年代:1995

数据来源: WILEY

摘要:

The Intergovernmental Panel on Climate Change (IPCC) has defined a set of scenarios for future CO2concentrations stabilizing at levels of 350 to 750 ppmv. Using models previously employed by IPCC, the implied global‐mean temperature and sea level changes are calculated out to 2500. While uncertainties are large, the results show that even with concerted efforts to stabilize concentrations of greenhouse gases, substantial temperature and sea level increases can be expected to occur over the next century. Increases in sea level are likely to continue for many centuries after concentration stabilization because of the extremely long time scales associated with the deep ocean (which influences thermal expansion) and with the large ice sheets of Greenland and Antarctic

ISSN:0094-8276    

DOI:10.1029/94GL01011

年代:1995

数据来源: WILEY

摘要:

We conducted year‐round measurements of mid infrared atmospheric emission over the South Pole in 1992. We were able to observe a large seasonal change of the total column of nitric acid (HNO3) vapor. During the summer, the HNO3column abundance was about 2×1016molecules/cm². There was a small increase in the fall. A rapid decrease of 50% was observed in late June, soon after the stratospheric temperature reached the threshold for formation of type I polar stratospheric clouds (PSCs). By early July, the stratospheric temperature was cold enough to form type II PSCs, and the HNO3column decreased to 7×1015molecules/cm². Measured nitric acid values in the spring remained extremely low even after the stratosphere warmed well above PSC temperatures. This may indicate permanent removal of HNO3by gravitational settling, or long‐term sequestering in large particles. Normal summer values were not observed until the vortex dissipated and allowed the lateral transport of HNO3, to the south polar

ISSN:0094-8276    

DOI:10.1029/94GL02794

年代:1995

数据来源: WILEY

摘要:

With a double monochromator, high resolution spectral measurements of direct solar UV‐irradiance were performed in Arosa during February and March, 1993. Total atmospheric ozone amount is determined by fitting model calculations to the measured spectra. The results are compared with the operationally performed measurements of a Dobson and a Brewer spectrometer. The total ozone amount determined from spectral measurements differs from the results of the Dobson instrument by −1.1±0.9% and from those of the Brewer instrument by −0.

ISSN:0094-8276    

DOI:10.1029/94GL02836

年代:1995

数据来源: WILEY

摘要:

Since the explosive volcanic eruption of Mt. Pinatubo on June 15, 1991, extensive lidar observations at a wavelength of 532 nm have been made at Tsukuba and Naha in the northern hemisphere and Lauder in the southern hemisphere. The first increase of the aerosols from the Pinatubo eruption was observed at 15.7 km over Tsukuba on June 28, 1991. From fall 1991, the Pinatubo aerosol particles were effectively transported from the tropical region into the northern mid‐latitude. The maximum scattering ratios observed were 14.1 at 22.7 km on November 29, 1991 at Tsukuba and 22.5 at 25.9 km on December 4, 1991 at Naha respectively. The Lauder measurements started in November 1992, too late to pick up the Pinatubo maximum. The maximum values of integrated backscattering coefficient (IBC) above the tropopause were 5.4×10−3sr−1over Naha on November 18, 1991 and 7.1×10−3sr−1over Tsukuba on February 22, 1992 respectively. The IBC over Tsukuba showed clear seasonal variation with a maximum in winter and early spring and a minimum in summer. The IBC over Tsukuba in winter of 92/93 decreased only about 26 percent compared with the IBC in 91/92 winter, but the IBC in winter of 93/94 decreased largely. The IBC over Lauder was significantly larger than those over Tsukuba and Naha from June 1993 to

ISSN:0094-8276    

DOI:10.1029/94GL02735

年代:1995

数据来源: WILEY

摘要:

The application of an advanced spectral estimation procedure, the multitaper method, to time series of stratospheric field variables is explored. New information on inherent cyclic variations is extracted from the time series of total ozone at Reykjavík, local 30 hPa temperatures and the equatorial zonal winds. Apart from the annual component, strong signatures of 8.6 months periodicity appear in the Dobson data for the period 1978 to 1990. The same harmonic component is successfully detected in the data from the total ozone mapping spectrometer (TOMS) and the longer term equatorial zonal winds, implying a low latitude dynamically induced cyclic variation of global significance. A spurious semi‐annual signal detected in the Dobson data is due to the non‐homogeneous sampling rate of the instrument throughout the year. The amplitude and phase of both the annual and 8.6 months line components of the Dobson and TOMS time series show excellent agree

ISSN:0094-8276    

DOI:10.1029/94GL02834

年代:1995

数据来源: WILEY

摘要:

VHF radar measurements have been made for 32 days in the summer polar mesosphere at Andenes (69°N, 16°E) in Northern Norway. For specific time intervals a significant correlation between wave‐induced velocity oscillations and corresponding echo power variations has been found. In particular, the height dependence of amplitude and phase of the different waves has been studied in detail. The observed waves in the velocity field, which are also present in the temperature field, occasionally appear in corresponding echo power variations possibly due to the existence of ice particles in the summer polar mesosph

ISSN:0094-8276    

DOI:10.1029/94GL02902

年代:1995

数据来源: WILEY

摘要:

A ∼2‐ms transition in auroral electron precipitation observed by the TESP electron spectrometer on Freja is described. The lack of significant pitch‐angle dependent velocity dispersion in the observations implies that the transition is a ∼10‐m spatial, rather than temporal, boundary. There is no evidence of associated changes in the accelerating potential. Either the source population, or the mechanism allowing entry of the source population to the acceleration region, must provide for the sharp observed transitions. The energy fluxes are such that the regions of stronger precipitation are marginally vis

ISSN:0094-8276    

DOI:10.1029/94GL02555

年代:1995

数据来源: WILEY

摘要:

Energetic particle dropouts were observed in the local morning sector with the particle spectrometer S321 onboard the European geostationary satellite GEOS‐2. The dropouts usually last 10 to 30 minutes. They differ from those commonly observed in the midnight sector during growth phases of substorms and also from magnetopause crossings. They occur during the recovery phase and are well inside the magnetosphere. During the dropouts the total magnetic field increases. Ground magnetic recordings and AE indices show that the dropouts are related to the substorm recovery phase during multiple substorm events. Ground magnetic recordings also reveal that in the majority of the cases a new substorm activation is seen in the midnight sector simultaneously with the recovery phase signatures in the morning sector. The dropouts are most likely associated with locally thinning of the morning side plasma shee

ISSN:0094-8276    

DOI:10.1029/94GL02910

年代:1995

数据来源: WILEY

摘要:

We employ data from two spacecraft, at the dawn flank of the magnetopause, to investigate fluctuations in the thickness of the low‐latitude boundary layer (LLBL). We show the LLBL is considerably thinner shortly after the detection of a flux transfer event than it was during the event. These data are shown to be consistent with the theory of transient increases in the open LLBL thickness caused by a pulse of enhanced reconnection at the magnetopaus

ISSN:0094-8276    

DOI:10.1029/94GL02835

年代:1995

数据来源: WILEY