摘要:

Airborne measurements of NOx, NOy, CO, and O3were conducted in the vicinity of a line of towering cumulus and cumulonimbus clouds (approximate altitude, 9 km) in south‐central Oklahoma, on the afternoon of June 17, 1985. NOx, NOy, and CO concentrations in the upper tropospheric outflow region of these clouds were near environmental levels. Meteorological analyses show that these clouds were located above a cold front, which prevented the entry of air from the boundary layer directly below and near the cloud. Examination of the [NOy]/[CO]and [NOx]/[CO]ratios, as well as determination of the lifting condensation level and other thermodynamic analyses, indicated that the most likely origin of the air in the cloud outflow region was the layer immediately above the top of the boundary layer, which was quite clean. It appears that very little NOywas available to be scavenged by the clouds. The results for this case suggest that the large amount of vertical trace gas transport that has been noted in previous observations and model results cannot simply be extrapolated to all convective cells. The results also show the usefulness of CO as a conserved trace

ISSN:0148-0227    

DOI:10.1029/JD093iD01p00759

年代:1988

数据来源: WILEY

摘要:

A Garrett‐Munk‐type spectrum, describing in the frequency–wave number space the energy per unit mass distribution of the atmospheric buoyancy wave field, is derived from experimental spectra of the field variables, within the following constraints: (1) the spectral modeling must refer only tokzspectra, in order to minimize the spectral contributions of the possibly coexisting quasi‐two‐dimensional turbulence and; (2) the resulting model must correspond to a saturated wave field in its high wave number limit. A spectral dependence on intrinsic frequencies is estimated from the ratios of experimental temperature and vertical velocitykzspectra, obtained by balloon‐borne instrumentation. These results and previously published horizontal velocitykzspectra allow determination of the model spectrum parameters, which differ substantially from those proposed by VanZandt (1982). This resulting model spectrum is characterized by a nearly universal high wave number limit (with a −3 spectral slope) and a total energy that varies, mainly with altitude. Two typical atmospheric conditions, characterized by high or low vertical velocity variances, are, however, much better represented using two slightly different parameter sets. Then, the model spectra account for most experimental mesoscale rangekz,kH, and frequency spectra. As a tentative interpretation, it is suggested that these two conditions are associated with the presence or absence of a turbulent buoyancy subrange, while, in both cases, the energy levels within the saturated subrange imply strongly interactin

ISSN:0148-0227    

DOI:10.1029/JD093iD01p00774

年代:1988

数据来源: WILEY

摘要:

We study the interactions between the geochemical cycles of carbon and long‐term changes in climate. Climate change is studied with a simple, zonally averaged energy balance climate model that includes the greenhouse effect of carbon dioxide explicitly. The geochemical model balances the rate of consumption of carbon dioxide in silicate weathering against its release by volcanic and metamorphic processes. The silicate weathering rate is expressed locally as a function of temperature, carbon dioxide partial pressure, and runoff. The global weathering rate is calculated by integrating these quantities over the land area as a function of latitude. Carbon dioxide feedback stabilizes the climate system against a reduction in solar luminosity and may contribute to the preservation of equable climate on the early Earth, when solar luminosity was low. The system responds to reduced land area by increasing carbon dioxide partial pressure and warming the globe. Our model makes it possible to study the response of the system to changing latitudinal distribution of the continents. A concentration of land area at high latitudes leads to high carbon dioxide partial pressures and high global average temperature because weathering of high‐latitude continents is slow. Conversely, concentration of the continents at low latitudes yields a cold globe and ice at low latitudes, a situation that appears to be representative of the late Precambrian glacial episode. This model is stable against ice albedo catastrophe even when the ice line occurs at low latitudes. In this it differs from energy balance models that lack the coupling to the geochemical cycle of car

ISSN:0148-0227    

DOI:10.1029/JD093iD01p00791

年代:1988

数据来源: WILEY

摘要:

Experiments were made with an atmospheric general circulation model coupled to a 50‐m mixed layer ocean in order to study the sensitivity of the climate to the changed seasonal and latitudinal distribution of solar radiation for 9000 years ago. At 9000 years B.P. (before present), when perihelion was in July (compared to January at present) and the axial tilt was greater than at present, the July (January) solar radiation in the northern hemisphere was increased (decreased) by about 7% compared to that at present. The coupled atmosphere/ocean model simulated warmer continents in summer and intensified northern summer monsoons at 9000 years B.P., compared to the present, that were similar to previous results with an atmospheric model. Owing to small positive feedbacks, the coupled atmosphere/ocean model produced a slightly greater intensification of the 9000‐year B.P. monsoon than the atmospheric model. The ocean temperature changes were less than 1 K and lagged the solar radiation changes; the 9000‐year B.P. ocean was warmer in September and colder in March than the control simulation. The annual‐average ocean temperature was slightly lower in the tropics because the annual‐average incoming solar radiation was lower at 9000 years B.P. In middle latitudes the annual‐average ocean temperature was decreased because of feedbacks associated with seasonality. In high northern latitudes, sea ice thickness was reduced at 9000 years B.P. in response to increased summer and annual‐average solar radiation. The reduced high‐latitude sea ice caused somewhat warmer wintertime conditions over the northwestern portions of nort

ISSN:0148-0227    

DOI:10.1029/JD093iD01p00803

年代:1988

数据来源: WILEY