摘要:

Water vapor is released into the Goddard Institute for Space Studies (GISS) global climate middle atmosphere model at the locations and cruise altitude of subsonic aircraft. A range of water vapor values is used to simulate not only current and 2015 projected emissions but also to provide larger signal‐noise ratios. The results show that aircraft water vapor emissions do not significantly affect the model's climate, either at the surface or in situ. With emissions some 15 times higher than the 2015 projection, a small impact is observed, amounting to a few tenths degrees Celsius globally and locally, while with emissions 300 times the 2015 values, a global warming of 1°C results. However, with releases this large, only about 5% actually stays in the atmosphere. The larger emissions increase the specific humidity most in the tropical lower troposphere, partly as a result of increased evaporation due to the global warming; at flight altitudes, relative humidity and cloud cover increase at latitudes of emission, and temperature decreases. Surface warming is relatively independent of latitude, and only a slight longitudinal aircraft footprint is found in the warming for the most extreme experiment. Comparison to increased CO2experiments of similar magnitude warming shows that the upper tropospheric response is greater in the water vapor release experiments, but the high‐latitude surface temperature response is larger with increased CO2due to more effective cryospheric feedb

ISSN:0148-0227    

DOI:10.1029/96JD02747

年代:1996

数据来源: WILEY

摘要:

A 6‐year climatology of subvisual and opaque cloud occurrence frequencies is established using observations from the Stratospheric Aerosol and Gas Experiment (SAGE) II between 1985 and 1990. The subvisual clouds are observed mostly at high altitudes near the tropopause. The opaque clouds terminate the profiling, reducing the measurement frequency of the SAGE II instrument in the troposphere. With its 1‐km vertical resolution, the climatology shows many interesting features, including (1) the seasonal expansion and migration behavior of the subvisual and opaque cloud systems; (2) the association of the zonal mean cloud frequency distributions with the tropospheric mean circulation (Hadley and Ferrel cells); (3) the tropical cloud occurrence that follows the equatorial circulation, including the Walker circulation over the Pacific Ocean; and (4) the overall higher cloud occurrence in the northern hemisphere than in the southern hemisphere. The radiative impact of subvisual clouds is estimated to be a 1‐W m−2reduction in outgoing longwave radiation. The maximum overall effect is a net positive cloud forcing of 0.5–1 W m−2in the tropics. During the 1987 El Niño‐Southern Oscillation (ENSO), cloud frequency was generally enhanced in the tropics and midlatitudes and reduced in the subtropics and high latitudes. The present study shows a distinct negative correlation between the high‐altitude cloud occurrence and the lower stratospheric water vapor mixing ratio in the tropics, providing intrinsic evidence on the delicate connection between the stratospheric‐tropospheric exchange and dehydration processes and the high‐altit

ISSN:0148-0227    

DOI:10.1029/96JD01780

年代:1996

数据来源: WILEY

摘要:

Six rainfall data time series, collected in various sites in Italy, are analyzed in order to determine whether a linear trend or long memory is present. Various techniques for estimating the intensity of long memory are applied, including the rescaled range statistic, the aggregated variance method, the periodogram method and maximum likelihood. A modified variance‐type estimator is used in order to detect long memory even when some types of nonstationarity are potentially present. The results indicate that a decreasing trend, though not statistically significant, is present in every record, and that long memory is significant in only two serie

ISSN:0148-0227    

DOI:10.1029/96JD02512

年代:1996

数据来源: WILEY

摘要:

An investigation of clear sky spectral radiances and their applicability as a diagnostic for climate variability is described. Global observations of outgoing longwave radiation during 1970 from the infrared interferometer spectrometer (IRIS) aboard Nimbus 4 cover nearly a full annual cycle, and the spectral content of the data provides unique information for examining regional and seasonal variations of spectral radiance. The IRIS radiances have been validated against a line‐by‐line radiative transfer model and are found to compare favorably with calculated radiances. A brightness temperature threshold technique is used to separate clear and cloudy spectra, and seasonal means of clear sky spectra are analyzed for tropical and northern midlatitude ocean areas. Brightness temperature standard deviations are also examined spectrally. Values of 1–2 K in the tropics and 2–3 K at midlatitudes in the 800–1200 cm−1window region are consistent with observed ocean temperature variability. Spectral features in the standard deviations reflect the variation of surface temperature, tropospheric temperature, and water vapor in the tropics and the increased variability of ozone during winter in the northern hemisphere. Spectral differences between seasonal and annual mean outgoing radiance are associated with variations in atmospheric parameters, and a linear retrieval algorithm is used to quantify these changes in the tropics. Retrieved seasonal sea surface temperature (SST) differences are typically within 0.7 K of the observed SST differences. Interseasonal water column variations during this annual cycle are 5–10% over the tropical Pacific and Atlantic and 10–20% over the equatorial Indian Ocean. In general, the retrieved seasonal changes in temperature and water vapor parameters are consistent with the known conditions of the 1970 tropical ocean and atmosphere. These variations are detectable as signatures in outgoing spectral radiances and provide significant information relevant to

ISSN:0148-0227    

DOI:10.1029/96JD02585

年代:1996

数据来源: WILEY

摘要:

We studied effects of the cloud inhomogeneity in subcloud scale on the reflectance, transmittance, and absorptance of two‐dimensional, inhomogeneous clouds. We generated the inhomogeneous clouds as multifractal clouds with a lognormal multiplicative process. For such clouds, the information codimensionC1is a measure of the cloud inhomogeneity. Radiative transfer through the multifractal clouds was computed with a discrete angle radiative transfer model. The average reflectance, transmittance, and absorptance of multifractal clouds with a given codimension were estimated as averages of 200 realizations. They were computed for different sets of theC1parameter, cloud total optical thickness, and asymmetry factor of cloud scatterers. An effective optical thickness of inhomogeneous clouds was defined empirically in the framework of a homogeneous, plane parallel cloud model. Consequently, computation of radiative flux in an inhomogeneous cloud could be transformed into that of an equivalent homogeneous, plane parallel cloud. For a two‐dimensional, inhomogeneous, absorbing cloud we found that an inhomogeneous cloud absorbs generally less energy than its homogeneous counterpart. An exception was found for inhomogeneous clouds characterized by a small information codimension, a large cloud optical thickness, and a large single‐scattering albedo and for which absorptance is much larger than for their homogeneous counterpart. However, this increase was less than 5% of the homogeneous cloud absorptance. The use of the effective optical thickness also enabled us to treat an inhomogeneous absorbing cloud as an equivalent homogeneous absorbing cloud and to estimate the radiative flux of the equivalent homogeneous cloud as an approximation to the one in the inhomogeneous cloud. We found no immediate need to conceive of a direct effect of the cloud inhomogeneity on the single‐scattering albedo, as far as we considered this treatment as a first‐order approximation. We discussed the use of the effective optical thickness in two‐stream radiative approximations. We also compared our results with those based on the independent pixel ap

ISSN:0148-0227    

DOI:10.1029/96JD02200

年代:1996

数据来源: WILEY

摘要:

A simple model for estimating the upward and downward microwave emission from rain layer types above ground is presented. The emission properties of the rain layers are estimated from physical quantities such as the optical depth, the single‐scattering albedo, the physical temperature, and a given drop size distribution for Mie scattering calculations. The underlying surface is characterized by the emissivity and the physical temperature. The transparency coefficientqand the reflection coefficientrof the rain layer are expressed by these physical quantities. The brightness temperature then is given by the physical temperatureT,q, andr. The radiation transfer is estimated by the method of layer addition, described bySobolev[1956], which avoids the necessity of solving the equation of radiation transfer. The accuracy of this simple model was estimated by comparisons with three‐dimensional Monte Carlo calculations. The error is estimated to be less than 3 K for common situations and less than 8 K for unrealistic high optical depths. It is shown that any one of the quantities rain rate, rain layer depth, and physical temperature can be estimated with sufficient accuracy if the others are known. The basic model has been extended for application to inhomogeneous cloud layers and to include differences in brightness temperatures for horizontal and vertical polarizations for oblate raindrops. The main intended application of this model is rain rate estimation from space with low data processing efforts, especially for the Priroda mission. The model was tested for the downwelling emission during the field experiment CLEOPATRA by measurements with a polarimetric weather radar and rain gauges. The results verify the principles, and promising agreement was found at least for stratiform rain. The polarimetric extension of the model too showed promising results under quite different measurement conditions in Russia and southern Germ

ISSN:0148-0227    

DOI:10.1029/96JD02244

年代:1996

数据来源: WILEY

摘要:

The assessment of the effects of atmospheric inputs on the chemistry of mountain lakes requires realistic data on the chemical composition of these inputs. However, precipitation sampling stations are usually at lower altitudes than lakes. The location of the stations may lead to a mistaken appraisal of precipitation chemistry, since orography strongly influences the formation of storms caused by air masses coming from different directions, and altitude affects the mechanisms of transport and deposition of solutes in several ways. The effect of altitude on the chemistry of precipitation in the Pyrenees was studied at three sampling points located at different heights (1600, 1900, and 2200 m above sea level) within the same valley, orientated in a NE‐SW direction. Sampling was carried out over a period (summerautumn 1990) long enough to ensure a statistically representative collection of events with a different origin. Three main results were derived from this study. (1) The main source of variability was the cation‐anion balance, which was determined by the origin of the wet air masses: rains from the Atlantic were more acidic than those coming from the Mediterranean. (2) There was no significant difference in the chemistry of bulk precipitation with altitude within the range 1600–2200 m asl, in which most of the lakes in the Pyrenees are found. (3) Below‐cloud mechanisms of deposition had a significant influence on NO−3concentration. The concentration of most of the solutes was independent of precipitation volume, except

ISSN:0148-0227    

DOI:10.1029/96JD01816

年代:1996

数据来源: WILEY

摘要:

The water‐soluble fraction of atmospheric aerosol particles is a major property dividing the particle population into cloud condensation nuclei and interstitial particles during cloud formation. Likewise, this property influences cloud microphysics and chemistry as well as direct and indirect aerosol forcing of climate. Up to now this important parameter has been only poorly determined experimentally. Here, we present SoFA, a new method to determine the water‐SolubleFraction of large and giantAerosol particles in five narrow size bands with geometrical radii of 0.4, 0.6, 0.9, 1.3, 1.8 μm and one band for particles with radius larger than 2.3 μm. First results show three different types of aerosol particles (AP I, II, III). AP I were characterized by 9% water‐soluble material, and AP II by 50% and correspond to those found in earlier studies for small particles. The new AP III consists of 88% water‐soluble material. In those size bands, where all three particle types could be detected (0.9, 1.3, and 1.8 μm because of detection limits of SoFA, only two types of particles could be detected in the remaining size bands), about 50% of the total number of analyzed particles belong to AP III, whereas about 25% belong to both APII and I. These numbers lead to 59% water‐soluble material on average. Particles of AP III are assumed to be cloud‐processed particles, those of AP I might be of biological origin. The impact of the water‐soluble fraction of particles on cloud microphysics is investigated by comparing two cloud situations using an entraining air parcel model with detailed microphysics. The model simulations show an influence on nucleation scavenging, cloud interstitial aerosol, and in particular, drop size population. Most notable is that the same aerosol particle number distribution causes either a precipitating or a non precipitating cloud, depending only upon different water‐soluble fraction

ISSN:0148-0227    

DOI:10.1029/96JD02245

年代:1996

数据来源: WILEY

摘要:

A statistical procedure is developed to obtain the parameters of spectral harmonics of internal gravity waves (IGW) with horizontal wavelengths larger than ∼ 60 km using measurements of wind velocity in the middle atmosphere from the middle and upper atmosphere (MU) radar. The method is applied to find sets of IGW parameters for the winter and summer seasons of 1987–1988 for 6‐km‐thick layers centered at 70, 75, and 80 km at Shigaraki, Japan (34.9°N, 139.4°E). The numbers of selected IGW harmonics having periods from 5 min up to 6 hours vary between 360 and 2000 depending on the season and altitude. Mean vertical wave numbers are 0.6–0.9 km−1in winter and 0.5–1 km−1in summer, and horizontal wave numbers are (3–4)×10−2km−1and (2–4)×10−2km−1, respectively. Predominant azimuths of wave vectors and momentum fluxes concentrate near 64° in winter and 90° in summer at all altitudes. In general, the difference between the azimuths of the wave vector and momentum flux is close to zero or 180°. Turbulent and instrumental noise can contribute 20–30% of the observed intensity of the wind variations at altitudes of 70–85 km. The IGW momentum fluxes are 0.2–2.7 m2s−2in winter and 0.2–1.9 m2s−2in summer. The wave drag of the mean flow is 0.5–45 m2s−1in winter and 2–25 m2s−1in summer. In most cases the momentum flux

ISSN:0148-0227    

DOI:10.1029/96JD01447

年代:1996

数据来源: WILEY

摘要:

Several transport scenarios have been advanced in the literature to account for the exchange of tracers between the extratropics and tropics in the lower stratosphere. Each scenario involves a slow, net upward transport at low latitudes and varying degrees of mixing at middle latitudes plus detrainment across a subtropical region of enhanced tracer gradients. In situ observations for differentiating among these scenarios are generally lacking above about 21 km altitude. Existing satellite data sets can provide useful information throughout the lower stratosphere. In particular, we have looked for such exchange by examining time series of the daily zonal variance of the Nimbus 7 limb infrared monitor of the stratosphere distributions of nitric acid vapor (HNO3) mixing ratio. This species is characterized by strong subtropical meridional gradients between about 10 and 100 hPa, which develop in response to extratropical wave activity and any associated mixing processes. The subtropical variance is a measure of that activity, its region of maximum values moving equatorward during late autumn and then relaxing and retreating in late spring. At and below the 45‐hPa level there is not a clear maximum of variance at a given latitude, perhaps a result of the secondary circulation that was present during the 1978/1979 winter in response to the easterly phase of the quasi‐biennial oscillation cycle. At the 30‐hPa and 50‐hPa levels, while we find occasions in winter when tongues of subtropical air were transported to higher latitudes, we find no clear evidence for a large‐scale transport of extratropical air to lower latitudes through a subtropical region of enhanced

ISSN:0148-0227    

DOI:10.1029/96JD02804

年代:1996

数据来源: WILEY