摘要:

A three dimensional linear model of orographically forced gravity waves (mountain waves) using realistic topography is used to simulate a high altitude (20 km) ER‐2 encounter with a large mountain wave over Alexander Island (72° W, 69° −72° S). Reasonable agreement between the linear model and observations is obtained if the effects of low‐level flow blocking are taken into

ISSN:0094-8276    

DOI:10.1029/GL017i001p00081

年代:1990

数据来源: WILEY

摘要:

After removal of the ∼ 11,000‐year geomagnetic contribution to a relatively high‐precision atmospheric Δ14C record covering the past 7200 years, residual variations exhibit a 2200–2600 year quasi‐periodicity that has been recognized in earlier studies. We find here that century‐scale variations in the most recent ‘cycle’ are positively correlated with similar short‐term variations in each of the two previous cycles. Thus the quasi‐periodicity consists of both a long‐term variation of the mean and a superposed, approximately recurring pattern of century‐scale variations. The strongest of these latter variations occur near successive maxima of the ∼ 2400 year cycles. During the last millennium, the largest century‐scale variations (occurring near the most recent 2400 year maximum) are known to be mainly a consequence of the pronounced Maunder, Spörer, and Wolf solar activity minima. Therefore, the recurrence of large amplitude Δ14C variations at 2400 year intervals is most directly explained as due to solar forcing at both the ∼ 2400 year and century‐scale periods. A fully terrestrial 2400 year modulation of an independent century‐scale solar forcing function is disfavored by the joint occurrence of relatively strong Δ14C maxima and solar activity minima during the current millennium, according to independent proxy records. The probable existence of a ∼2400 year solar quasi‐cycle has implications for the predictability of future pronounced solar activity minima and for the interpretation of c

ISSN:0094-8276    

DOI:10.1029/GL017i001p00085

年代:1990

数据来源: WILEY

摘要:

A laser ceilometer, an acoustic sounder, and a microwave radiometer were used to estimate cloud thickness and the adiabatic and integrated liquid water content of shallow stratocumulus clouds continuously for three days using two‐minute averages. Although the observed liquid water path was close to the theoretical adiabatic value for most of the three days, there was one four‐hour period when the liquid water content dropped to about 50% of the adiabatic value. Hourly‐averaged values for a 19‐day period of intensive observations show that the cloud water content was generally close to the adiabatic value. Occasionally there were clouds greater than 300 m in depth in which the water content was clearly less than ad

ISSN:0094-8276    

DOI:10.1029/GL017i001p00089

年代:1990

数据来源: WILEY

摘要:

The factors for controlling the photochemical generation of gaseous H2O2were studied on the basis of both field data and model predictions. Field data of the concentration of gaseous H2O2at ground‐level were obtained in west Los Angeles during 1985–88. The results indicate that there is a clear seasonal trend of gaseous H2O2(0.03–1.35 ppb, n=150) with highest concentrations in the summer. Statistical analyses revealed that the concentration of H2O2increases with increasing solar radiation at a statistically significant level. A one‐dimensional photochemical model, which is based on the prevailing meteorological conditions and primary pollutants loading in Los Angeles, also predicted that solar radiation is the major factor in determining the formation rate of H2O2in the atmosphere. These results indicate that solar radiation significantly controls the formation of gaseous H2O2. Considering the low photochemical activity in the winter, H2O2is probably limiting for the oxidation of SO2in the Los Angeles winter atmosphere where the SO2content exceeds the H2O2concentrations. Our results also imply that, if the UV radiation in the troposphere increases due to the depletion of the stratospheric O3content, the H2O2levels will increase and as a result the production of sulfuric acid will increase in the winter atm

ISSN:0094-8276    

DOI:10.1029/GL017i001p00093

年代:1990

数据来源: WILEY

摘要:

Multibeam bathymetric data is modeled from a Bayesian “smoothness priors” framework. Smoothness priors is a penalized likelihood‐nonparametric linear regression form of modeling and the bathymetry data are modeled one beam at‐a‐time. The method is applied to data previously analyzed in Goff and Jordan (1988) and Gilbert and Malinverno (1988). The results contrast nonparametric and parametric modeling, dispute the almost conventional removal of “deterministic” components prior to stochastic modeling and reveal new evidence about mid‐ocean ridge spre

ISSN:0094-8276    

DOI:10.1029/GL017i001p00097

年代:1990

数据来源: WILEY

摘要:

New data are used to examine anomalously shallow paleomagnetic inclinations derived from previous analyses of Cretaceous DSDP sediments of the central western Pacific Ocean. While VRMs are shown to produce a similar effect, the bias toward shallow values is still present with thoroughly demagnetized data. Superimposed upon this bias is a trend towards maximum flattening at an expected inclination of ∼55°, with the flattening falling to zero at the equator and pole. Flattening due to sediment compaction, or ‘inclination‐error’, is proposed to explain these obse

ISSN:0094-8276    

DOI:10.1029/GL017i001p00101

年代:1990

数据来源: WILEY

摘要:

A 2D numerical model study of a regional scale thermal anomaly along the north Spanish border of the Mediterranean Sea indicates strong lateral offshore heat transport due to groundwater circulation. Although the area is situated at the western side of the Valencia Trough rift zone, the amplitude and wavelength of this coupled negative‐positive anomaly cannot be explained by conductive heat flow. A strong hydraulic gradient onshore and a thick layer of permeable Mesozoic limestones should permit lateral advection of pore water about 30 km offshore where discharge creates anomalous temperature gradients. This result underscores the importance of deep groundwater flow even in the interpretation of regional scale thermal anomalies in rifting zone

ISSN:0094-8276    

DOI:10.1029/GL017i001p00105

年代:1990

数据来源: WILEY