摘要:

Differentiation of sea‐salt and non‐sea‐salt (or excess) components is essential for many studies of marine aerosol and precipitation chemistry. Uncertainties in such calculations arise from (1) uncertainties in the composition of seawater, (2) analytical uncertainties, (3) the amount of dry deposited sea salt in samples, (4) the validity of assuming a purely marine source for the sea‐salt reference species, and (5) the validity of assuming no fractionation during or after production of sea‐salt aerosols. We assessed these uncertainties, and, using the reduced major axis regression technique, evaluated these assumptions by analyzing the composition of precipitation at Amsterdam Island (38°S, 78°E) and at Bermuda (32°N, 65°W). Precipitation on Amsterdam Island contained significant excess concentrations of Na+(2%) and Cl−(5%) relative to Mg2+. Indirect evidence indicates that these departures from seawater ratios are probably not due to the influence of terrestrial material. The excess Cl−was sufficient to account for approximately 20% of free acidity, suggesting that scavenging of vapor phase HCl may affect the acid‐base chemistry of precipitation at the site. Volume‐weighted excess SO42−based on Na+and Mg2+differed by 11%, a nonnegligible source of bias in estimating the wet deposition of non‐sea‐salt sulfur. Precipitation on Bermuda contained significant concentrations of locally derived alkali and alkaline earth metals. The influence of continental and non‐sea‐salt marine sources on concentrations of excess SO42−was also evident. These observations suggest that assumptions involved in sea‐salt corrections are not always satisfied and that it is therefore necessary to evaluate individual data sets, using objective criteria, to selec

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06647

年代:1986

数据来源: WILEY

摘要:

Several approaches to detecting the existence of a theoretically predicted CO2‐induced signal in the global temperature field are investigated. It appears that a relatively thin network of observing stations can, when properly analyzed, provide a first‐order estimate of global‐scale temperature change and that this measurement is not necessarily the “global average” temperature. Using these stations, it is possible to estimate the strength of an a priori CO2signal in the three dimensional tropospheric temperature field. This signal is derived from two different general circulation model simulations, both with some form of interactive oceans. The observed signal strength over 1960–1980 is roughly 0.5–1.0 times that expected “theoretically.” The observed signal demonstrated a trend that is margi

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06659

年代:1986

数据来源: WILEY

摘要:

In a number of studies, various workers have used the procedure of fitting cubic splines with nodes spaced 12 months apart in order to remove seasonal effects from atmospheric CO2observations. A number of trial examples of least squares spline fits are presented, indicating that this procedure can be subject to relatively large end effects. For variations with periods near 2 years the response is extremely sensitive to the position of the nodes and shows beating effects caused by the change in the relative positions of the signal peaks and the spline nodes. A signal whose period is exactly twice the node spacing can either be passed almost unchanged or be completely filtered out, depending on its phase relative to the nodes of the spline. These properties make such spline fitting unsuitable for analyzing the interannual variations in CO2data.

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06668

年代:1986

数据来源: WILEY

摘要:

A new, accurate, and nondiffusive method for three‐dimensional advection of trace species is presented. The method preserves tracer structures by conserving the second‐order moments of the spatial distribution of tracer during advection. Tracer concentrations are represented by separate, second‐order polynomials within each grid box. This second‐order moments method has been shown, in typical tests for advective schemes, to be equal or superior to presently available methods in terms of absolute accuracy, numerical diffusion, and computation

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06671

年代:1986

数据来源: WILEY

摘要:

The sensitivity of the atmospheric seasonal cycle to ocean conditions and solar forcing is investigated using a low‐resolution spectral atmospheric general circulation model (GCM). The external forcing of the model is grouped into two basic categories: (1) ocean conditions (sea surface temperature and sea ice extent) and (2) radiation specifications (incoming solar radiation, albedo parameters involving cloud cover and land snow cover, and long‐wave emissivity coefficients). These forcing parameters are all prescribed with smoothly time‐varying seasonal cycle variations in the control simulation. In two sensitivity experiments, parameters in only one of the two forcing categories are allowed to vary seasonally; the others are fixed at their annual mean values. Analysis shows that model sensitivity to radiation specifications is effectively a solar‐forcing sensitivity. These experiments show that on a zonally averaged basis at mid‐latitudes in the northern hemisphere, the seasonal variations in the direct heating of the atmosphere and land surfaces by incoming solar radiation are generally more important than seasonal variations in the ocean forcing for determining the fundamental annual harmonic variations of temperature, pressure, zonal wind, and precipitation in the model. In fact, for many of these variables, even in the southern hemisphere, the simulation of the annual harmonics with the radiation forcing alone is not statistically different from simulation of the annual harmonics in the control case. Sea surface temperature and sea ice extent do play an important role in the fundamental harmonic variations in the southern hemisphere for sea level pressure and lower tropospheric temperature on a zonally averaged basis. At tropical latitudes, seasonal variation of sea surface temperature is critical for capturing the fundamental annual harmonic variations of low‐troposphere temperatures, sea level pressure, and precipitation, presumably due to the contributions of convective and boundary layer processes. The results presented in zonally averaged, horizontal map and vertical cross‐section formats, help to describe the variables and specific areas for which the nature of the formulation of the ocean component in an interactive ocean‐atmosphere model, especially in terms of its seasonal variation, will be an important consideration for simulation of the atmospheric annual harmonic cy

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06682

年代:1986

数据来源: WILEY

摘要:

The response of atmospheric ozone and temperature to variations in the solar ultraviolet irradiance over time scales corresponding to the solar rotation period is examined using a one‐dimensional, time‐dependent radiative‐photochemical model of the upper stratosphere and lower mesosphere. The model uses temporally varying measurements of the solar irradiance in the 120‐ to 300‐nm range made by the Solar Mesospheric Explorer satellite. Calculations of the amplitude and phase of the ozone response due to solar UV oscillations made by the model show that the effects of the coupling of radiation and photochemistry in the region near the stratopause may not be neglected. At 0.85 mbar, the computed 27‐day 0.6 K temperature variation decreases the amplitude of the corresponding ozone response over the solar rotation period by 25%. The occurrence of small phase leads (up to 1.5 days) in the response of ozone with respect to the solar UV variations may also be explained in light of the radiative‐photochem

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06695

年代:1986

数据来源: WILEY

摘要:

An analysis of the response of middle atmospheric ozone to short‐term variations in the solar ultraviolet irradiance is presented. Measurements of ozone from the Solar Mesosphere Explorer (SME) ultraviolet spectrometer (UVS) are compared to calculations of a one‐dimensional, radiative‐photochemical model of the upper stratosphere and lower mesosphere. SME UVS measurements in the 0.1‐ to 1‐mbar range suggest that tropical ozone responds to solar rotational variation when analyzed using both frequency and time domain techniques. Three periods during 1982 and 1983 were selected for the analysis. The solar irradiance during each period exhibited different spectral characteristics. A significant 27‐day variation in the solar irradiance at 205 nm was measured during mid‐1982, with an amplitude of 2.5%. Observations of ozone near the stratopause during this period showed a corresponding variation, with a 1.3% amplitude. Analysis of ozone variations at extratropical latitudes revealed different periodicities that were not correlated with solar variations. The amplitude of the measured response is, in all cases, systematically larger than theoretical calculations but is nonetheless in agreement when uncertainties in the analysis are considered. However, the observed phase lag of ozone with respect to the solar UV variations is generally not in accord with mode

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06705

年代:1986

数据来源: WILEY

摘要:

The variability of small‐scale atmospheric turbulence on time scales from a few minutes to the annual scale and at altitudes from about 4 to 20 km is studied using clear air Doppler radar data from Poker Flat, Alaska, and Platteville, Colorado. The variable used for this study is the refractivity turbulence structure constantCn2. The frequency distribution ofCn2is found to be lognormal during all seasons at all altitudes. Using data at 4‐min intervals, it is found that the autocorrelation function ofCn2can be modeled as the sum of a first‐order autoregressive process and a random process. The associated integral time scale decreases with altitude from 25 to 45 min in the troposphere to about 18 min in the stratosphere. The power spectrum of logCn2follows a power law relation with frequency; at periods greater than about 2 hours the spectral slope is near −5/3 and at periods less than 2 hours the slope is near −1. Monthly mean values of logCn2are largest in the winter and show a secondary maximum in summer. The winter peak is apparently related to increased jet stream and baroclinic storm activity, and the summer peak is believed to be due to convective activity. The correlation of 3‐hour values ofCn2with wind speed over month‐long periods ranges as high as 0.8 and has a median value near 0.3. During certain periods,Cn2also depends on other variables such as boundary layer inversions and gravity wave activity. Monthly mean values ofCn2correlate more closely with an indicator of the intensity of gravity wave activity than with wind speed or the coarse‐scale wind shear. The meteorological significance of these results is di

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06722

年代:1986

数据来源: WILEY

摘要:

An analysis was made of data collected from automatic weather stations (AWS) on the slope of Adelie Land, Antarctica. The data were collected simultaneously at different stations on the ice‐covered slope of the continent, where no data have previously been obtained. The stations are classified into three groups according to their location (high plateau, intermediate plateau, or coastal region), each having distinct annual temperature and wind speed regimes. These classifications also correspond well to the stations' slopes. Change in surface air temperature along the slope with respect to height was smaller than −1°C/100 m between the high plateau and the intermediate plateau stations. The wind directions did not follow Ball's model, which suggests the importance of the gradient of surface potential air temperature along the slope on the wind regime. A scale analysis showed the condition in which the gradient of surface potential air temperature along the slope should not be considered negligible when considering the total pressure gradient force. This condition in turn indicates that the entrainment of momentum across the top of the katabatic wind layer is also impor

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06735

年代:1986

数据来源: WILEY

摘要:

The process Na + O2+ M → NaO2+ M apparently is the first in a sequence of reactions which chemically controls the sodium content of the mesosphere. The effectiveness of this reaction is reduced by NaO2+ O → NaO + O2, which generates only one tenth as much NaO as does the Chapman process Na + O3→ NaO + O2, using current rate coefficients. Hence Chapman's mechanism, which requires the formation of some Na(2P) when NaO reacts with O, remains the principal source of the sodium D‐lines at night. However, the net loss of sodium by Na + O3→ NaO + O2is small since the reaction between NaO and O is fast and since [O]≫[O3] in the mesosphere. The chemistry of the nightglow, a catalytic cycle with sodium as the catalyst, is shown to be virtually uncoupled from that of the sodium content. It follows that seasonal variations of the content and the nightglow can be fairly independent of each other, as has been observed. Observations that both mesospheric ozone and the sodium nightglow attain maxima during the equinoxes is in qualitative accord with the Chapman mechanism as the dominant source of the sodium nightglo

ISSN:0148-0227    

DOI:10.1029/JD091iD06p06742

年代:1986

数据来源: WILEY