bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of the global CFC 11 using the Los Alamos chemical tracer model
Authors: Jim Kao Chih‐Yue , Tie Xuexi , Mroz Eugene , Cunnold Derek , Alyea Fred
Published: February 2012

A three‐dimensional global chemical tracer model (CTM) with a multiyear circulation provided from the Los Alamos general circulation model (GCM) is developed to simulate the distributions and trends of global CFC 11 concentrations. Realistic geographic emission patterns and parameterized photolysis rates are included in the model. The initial condition corresponds to the observed values in July 1978. The results of six model years from July 1979 to June 1985 are presented. Comparisons with the Atmospheric Lifetime Experiment (ALE) observations show reasonable agreement. The intrinsic features of the five ALE sites can be summarized as follows: Adrigole is sensitive to horizontal diffusion because it is located between the European and North American sources; Samoa and Tasmania are heavily influenced by the interhemispheric transport; and Oregon and Barbados require a better resolved flow pattern to receive the transport from their nearest sources. The modeled global budget in terms of interhemispheric burden difference, stratospheric loss rate, interhemispheric transport, and its associated time constant is comparable with that derived from a previous study. A model sensitivity test using a large (∼3 times) horizontal diffusion shows that it modestly improves certain aspects of the simulations at southern hemisphere ALE sites, however, at the cost of a greatly reduced interhemispheric burden difference and exchange time constant.
Variability of geophysical parameters from aircraft radiance measurements for FIFE
Authors: Jedlovec Gary J. , Atkinson Robert J.
Published: February 2012

Airborne multispectral images were collected on 2 days during the First ISLSCP Field Experiment (FIFE) to investigate the time and space variability of remotely sensed geophysical parameters over the study region. The data sets consisted of multiple overflights covering about a 60‐min period during late morning on June 4, 1987, and shortly after dark on the following day. Image data from each overpass were calibrated and Earth‐located with respect to each other using aircraft inertial navigation system parameters and ground control points. Normalized difference vegetation index (NDVI) values were generated from visible and near‐infrared imagery to characterize the greenness of the vegetation, its spatial variability, and its variation with changing sensor‐Sun‐viewing geometries. Land surface temperatures (LST) were derived using a split‐window formulation to investigate their spatial and temporal variability in relation to the NDVI values and other surface features and the variability between day and night observations. The results indicated that large variations in these parameters existed at small scales. Variability in NDVI values was large and was governed by the natural surface character and its use. Large variations of NDVI occurred with different sensor‐Sun‐vie wing geometries as a result of anisotropic reflection from the surface, atmospheric interference, and slope and aspect effects. LST was also highly varied. Positive land surface temperature changes, as a result of excess absorption of solar radiation, exceeded 4°C in 45 min over certain regions and were governed by land use and microtopography. Smaller negative temperature changes were observed at night. NDVI and LST values were inversely related, with fairly high correlations for certain surface features. The unique multispectral atmospheric mapping sensor (MAMS) measurements and the derived NDVI and LST data provided a better understanding of reflective and thermal properties within a heterogeneous region, as well as a quantitative description of their spatial and temporal variability, and served to better characterize important surface processes related to microclimate variability.
Aerosol optical depth retrievals over the Konza Prairie
Authors: Bruegge Carol J. , Halthore Rangasayi N. , Markham Brian , Spanner Michael , Wrlgley Robert
Published: February 2012

The aerosol optical depth over the Konza Prairie, near Manhattan, Kansas, was recorded at various locations by five separate teams. These measurements were made in support of the First ISLSCP Field Experiment (FIFE) and used to correct imagery from a variety of satellite and aircraft sensors for the effects of atmospheric scattering and absorption. The results from one instrument are reported here for 26 days in 1987 and for 7 days in 1989. Daily averages span a range of 0.05 to 0.28 in the midvisible wavelengths. In addition, diurnal variations are noted in which the afternoon optical depths are greater than those of the morning by as much as 0.07. A comparison between instruments and processing techniques used to determine these aerosol optical depths is provided. The first comparisons are made using summer 1987 data. Differences of as much as 0.05 (midvisible) are observed. Although these data allow reasonable surface reflectance retrievals, they do not agree to within the performance limits typically associated with these types of instruments. With an accuracy goal of 0.02 a preseason calibration/comparison experiment was conducted at a mountain site prior to the final field campaign in 1989. Good calibration data were obtained, and good agreement (0.01, midvisible) was observed in the retrieved optical depth acquired over the Konza. By comparing data from the surface instruments at different locations, spatial inhomogeneities are determined. Then, data from the airborne tracking sunphotometer allow one to determine variations as a function of altitude. Finally, a technique is proposed for using the in situ data to establish an instrument calibration.
Estimating the daily course of Konza Prairie latent heat fluxes using a modified Tergra model
Authors: Hope Allen S.
Published: February 2012

The Tergra model simulates the daily course of water and energy flows through the soil‐plantatmosphere system and was intended for use with remotely sensed data. In its original form, the model is not well suited to estimating spatial patterns of latent heat flux (λE) in the Konza Prairie since the determination of canopy resistance requires knowledge of vegetation height, and the defined relationship between leaf water potential and rc is specific to C3 plants. The canopy resistance component of Tergra was replaced by a routine that includes the calculation of minimum canopy resistance (rcm) from the normalized difference vegetation index (NDVI) and stress adjustment factors for leaf water potential and vapor pressure deficit to determine actual canopy resistance (rc). The relationship between rc and leaf water potential is defined for both C3 and C4 plants, and total λE is obtained from the sum of the proportional contributions from these two vegetation classes. The modified Tergra model (Tergra‐2) was tested using input and flux data collected at four First ISLSCP Field Experiment (FIFE) sites during three periods characterized by different soil moisture conditions. Tergra‐2 was found to be a good simulator of λE and in most cases gave substantially better results than those obtained using the original model. The greatest inaccuracy using Tergra‐2 occurred under extremely dry soil moisture conditions, whereas absolute errors for both models tended to increase around solar noon. Leaf water potential was the dominant stress factor affecting modeled rc. It was concluded that vapor pressure deficit and leaf water potential should not be regarded as completely independent factors affecting rc. A brief comparison of modeled and observed canopy temperatures is presented and discussed.
Optical effects of polar stratospheric clouds on the retrieval of TOMS total ozone
Authors: Torres O. , Ahmad Z. , Herman J. R.
Published: February 2012

Small areas of sharply reduced ozone density appear frequently in the maps produced from polar region total ozone mapping spectrometer (TOMS) data. These mini‐holes are of the order of 1000 km in extent with a lifetime of a few days. On the basis of measurements from ground‐based instruments, balloon‐borne ozonesondes, and simultaneous measurements of aerosol and ozone concentrations during aircraft flights in the Arctic and Antarctic regions, the appearance of polar stratospheric clouds (PSCs) are frequently associated with false reductions in ozone derived from the TOMS albedo data. By combining radiative transfer calculations with the observed PSC and ozone data, it is shown that PSCs located near or above the ozone density maximum (with optical thickness greater than 0.1) can explain most of the differences between TOMS ozone data and ground or in situ ozone measurements. Several examples of real and false TOMS mini‐hole phenomenon are investigated using data from the 1989 Airborne Arctic Stratospheric Expedition (AASE) and from balloon flights over Norway and Sweden.
Composition analyses of size‐resolved aerosol samples taken from aircraft downwind of Kuwait, spring 1991
Authors: Cahill Thomas A. , Wilkinson Kent , Schnell Russ
Published: February 2012

Analyses are reported for eight aerosol samples taken from the National Center for Atmospheric Research Electra typically 200 to 250 km downwind of Kuwait between May 19 and June 1, 1991. Aerosols were separated into fine (Dp < 2.5 μm) and coarse (2.5 < Dp 10 μm) particles for optical, gravimetric, X ray and nuclear analyses, yielding information on the morphology, mass, and composition of aerosols downwind of Kuwait. The mass of coarse aerosols ranged between 60 and 1971 μg/m3 and, while dominated by soil derived aerosols, contained considerable content of sulfates and salt (NaCl) and soot in the form of fluffy agglomerates. The mass of fine aerosols varied between 70 and 785 μg/3, of which about 70% was accounted for via compositional analyses performed in vacuum. While most components varied greatly from flight to flight, organic matter and fine soils each accounted for about 1/4 of the fine mass, while salt and sulfates contributed about 10% and 7%, respectively. The Cl/S ratios were remarkable constant, 2.4 ± 1.2 for coarse particles and 2.0 ± 0.2 for fine particles, with one flight deleted in each case. Vanadium, when observed, ranged from 9 to 27 ng/m3, while nickel ranged from 5 to 25 ng/m3. In fact, fine sulfates, vanadium, and nickel occurred in levels typical of Los Angeles, California, during summer 1986. The V/Ni ratio, 1.7 ± 0.4, was very similar to the ratios measured in fine particles from combusted Kuwaiti oil, 1.4 ± 0.9. Bromine, copper, zinc, and arsenic/lead were also observed at levels between 2 and 190 ng/m3. The presence of massive amounts of fine, typically alkaline soils in the Kuwaiti smoke plumes significantly modified their behavior and probably mitigated their impacts, locally and globally.
Tropospheric chemistry over the lower Great Plains of the United States. 1. Meteorology
Authors: Ryan William F. , Dickerson Russell R. , Huffman George J. , Luke Winston T.
Published: February 2012

Convective clouds and thunderstorms inject planetary boundary layer air with high concentrations of ozone (O3) and O3 precursors into the free troposphere. By altering the chemistry and radiative balance of the upper troposphere, these local actions can have global consequences. In order to extrapolate from individual observations to general trends we have devised a method to identify weather patterns conducive to convection in the southern or lower Great Plains in early summer and applied this method to meteorological and chemical data from a series of research flights carried out in June 1985. Previous studies have noted that weather patterns in the lower Great Plains in this season are characterized by alternating pulses of polar and maritime air masses and very frequent episodes of violent convection, usually in maritime conditions in advance of a surface cold front or along the frontal zone itself. In this study, a set of selection criteria is applied to surface and upper air meteorological data from central Oklahoma to distinguish the two meridional phases characteristic of this region: maritime and polar. A deep layer of moist, southerly flow and convective instability is encountered in the maritime regime, while the polar phase is convectively stable throughout the midtroposphere and much less conducive to convection. For the period 1980–1985 both maritime and polar regimes occur with a frequency of about 35% in May, while the maritime phase becomes dominant in June (53% maritime versus 20% polar). Within the maritime regime, conditions conducive to the development of severe storms are characterized by the presence of a dry, low‐level inversion that tends to inhibit scattered midday convection over a wide region while simultaneously enhancing the probability of larger thunderstorms and mesoscale convective systems. This “modified maritime” category accounts for approximately 25% of the total cases in May and in June. The instances of frontal passage account for approximately 15% of the total cases. Profiles, from the surface to 200 mbar, made on 18 flights of the NCAR Sabreliner in the 1985 PRESTORM project, are categorized according to the selection criteria. Part 2 of this study presents representative concentrations of ozone, carbon monoxide, and reactive nitrogen compounds as a function of altitude (0–12 km) for each category and discusses the implications of these findings.
Ray‐tracing simulation of the global propagation of inertia gravity waves through the zonally averaged middle atmosphere
Authors: Eckermann Stephen D.
Published: February 2012

The global propagation of large‐horizontal‐wavelength inertia gravity waves through a zonally averaged geostrophic wind and temperature climatology of the middle atmosphere is investigated using numerical ray‐tracing techniques. Strong meridional shear in the zonal wind acts to refract waves horizontally (azimuthally), leading to changes in the local propagation azimuth, horizontal wavelength, and ground‐based horizontal phase speed of the wave. Unlike other identified mechanisms which can produce such changes, this refraction effect is linear and does not require (nor forbid) that the wave amplitude be unstable for it to occur. Careful treatment of wave amplitudes indicates that such refracted waves are suppressed in amplitude far less by radiative damping and saturation than previous modeling has suggested, due to the use of a more accurate radiative damping parameterization. Refraction therefore is potentially important in modifying the waves' characteristics as they propagate through the middle atmosphere, and simulations reveal modifications which agree broadly with some observational data. Multiray simulations, using a horizontally isotropic source “spectrum” of waves with equal initial amplitudes, produce wave amplitudes at a height of 60 km which exhibit variations with latitude, season, and vertical wavenumber which have much in common with observations. A dearth of waves with large horizontal wavelengths also arises, in agreement with collated observations in the upper middle atmosphere. Significant differences in the latitude‐season structure of the mean wave amplitudes of the northern and southern hemisphere are simulated. The simulations reproduce the well‐known change in mean azimuthal wave propagation from eastward in summer to westward in winter, but the simulated westward phase invariably exceeds 6 months in duration, and in places the eastward summer phase is very weak and of limited duration. In addition, a smaller but nonetheless distinct poleward component to the mean propagation directions arises, due in part to horizontal refraction. Comparison of measured and simulated distributions of wave propagation azimuths reveals good agreement at some locations. Mid‐latitude winter distributions around North America are well simulated when only c = 0 waves are retained. However, significant differences also occur, which may reflect the importance of features omitted from this model, such as zonal atmospheric variability and/or wave source effects. These and other limitations of the present model are highlighted; it is recommended that subsequent simulations incorporate zonal refraction due to planetary Rossby wave structure, and that higher‐frequency waves be included so that the impact of refraction on the vertical flux of horizontal wave momentum can be assessed.
Determination of soil moisture distribution from impedance and gravimetric measurements
Authors: Ungar Stephen G. , Layman Robert , Campbell Jeffrey E. , Walsh John , McKim Harlan J.
Published: February 2012

Daily measurements of the soil dielectric properties at 5 and 10 cm were obtained at five locations throughout the First ISLSCP Field Experiment (FIFE) test site during the 1987 intensive field campaigns (IFCs). An automated vector voltmeter was used to monitor the complex electrical impedance, at 10 MHz, of cylindrical volumes of soil delineated by specially designed soil moisture probes buried at these locations. The objective of this exercise was to test the hypothesis that the soil impedance is sensitive to the moisture content of the soil and that the imaginary part (that is, capacitive reactance) can be used to calculate the volumetric water content of the soil. These measurements were compared with gravimetric samples collected at these locations by the FIFE staff science team. In addition to the five fixed locations, measurements were made throughout each of the IFCs along three transects underlying airborne push broom microwave radiometer (PBMR) flights and compared with the results of gravimetric sampling done in support of these flights. Examination of the data reveals that the impedance probe is a more consistent source of time series information than traditional measurements and is potentially more closely linked to the physical parameters which are both remotely sensible and required for surface energy/mass exchange determination.
Elemental tracers for the study of homogeneous gas phase oxidation of SO2in the atmosphere
Authors: Husain Liaquat , Dutkiewicz Vincent A.
Published: February 2012

A tracer technique for following the SO4formation from SO2oxidation in ambient air is reported. Like SO2, Se is emitted to the atmosphere during coal combustion. Both SO4‐ and Se‐bearing aerosols show similar physical behavior; Se, however, is not formed in the atmosphere. We have used this difference to determine in situ SO4formation from SO2oxidation. The technique uses SO4and Se concentrations measured at two points of an air mass system. Results from samples collected at Mayville, and 530 km downwind at Whiteface Mountain, New York, are reported. Air trajectories were used to isolate two time periods (one each during the summers of 1981 and 1983) when air masses traveled from the high‐SO2emission region in the Midwest to Mayville and then to Whiteface Mountain. Both periods were accompanied by hot and humid conditions across the Northeast and SO4, concentrations of the order of 30 μg/m3. An average SO4production rate of 1.0 μg/m3/h was obtained. A simple model based on the SO4/Se ratios at a series of sites suggests that the SO2gas phase oxidation rate was∼3% per hour.
A coordinated study of a storm system over the South American continent: 1. Weather information and quasi‐DC stratospheric electric field data
Authors: Pinto O. , Pinto I. R. C. A. , Gin R. B. B. , Mendes O.
Published: February 2012

This paper reports on a coordinated campaign conducted in Brazil, December 13, 1989, to study the electrical signatures associated with a large storm system over the South American continent. Inside the storm, large convective cells developed extending up to the tropopause, as revealed from meteorological balloon soundings. Quasi‐DC vertical electric field and temperature were measured by zero‐pressure balloon‐borne payload launched from Cachoeira Paulista, Brazil. The data were supported by radar and GOES satellite observations, as well as by a lightning position and tracking system (LPATS). The analysis of infrared imagery supports the general tendency for lightning strikes to be near to but not exactly under the coldest cloud tops. In turn, the radar maps located the strikes near to but outside of the most intense areas of precipitation (reflectivity levels above 40 dBz). The balloon altitude and stratospheric temperature show significant variations in association with the storm. The quasi‐DC vertical electric field remained almost during the whole flight in a reversed direction relative to the usual fair weather downward orientation with values as large as 4 V/m. A simple calculation based on a static dipole model of electrical cloud structure gives charges of some tens of coulombs. In contrast with most electric field measurements in other regions, no indication of an intensification of the vertical field in the downward fair weather orientation was observed. This fact is in agreement with past observations in the South American region and seems to be related to a particular type of storm that would occur with more frequency in this region. If so, such a difference may have an important role in the global atmospheric electrical circuit, considering that South America is believed to give a significant current contribution to the global circuit.
On the electromagnetic fields, Poynting vector, and peak power radiated by lightning return strokes
Authors: Krider E. Philip
Published: February 2012

The initial radiation fields, Poynting vector, and total electromagnetic power that a vertical return stroke radiates into the upper half space have been computed when the speed of the stroke, ν, is a significant fraction of the speed of light, c, assuming that at large distances and early times the source is an infinitesimal dipole. The initial current is also assumed to satisfy the transmission‐line model with a constant v and to be perpendicular to an infinite, perfectly conducting ground. The effect of a large ν is to increase the radiation fields by a factor of (1 ‐ β2 cos2 θ)−1, where β = ν/c and θ is measured from the vertical, and the Poynting vector by a factor of (1 ‐ β2 cos2 θ)−2. This increase is just a few percent or less at small β, but when β = 0.67, the fields are about 80% larger at small θ and 50% larger at θ = 30°, and the power that is radiated is increased by 26%. When β = 0.5 and the peak current is 30 kA, typical values for negative first strokes, the peak power that is radiated into the upper hemisphere is 1.0 × 1010 W.
Validation of cloud forcing simulated by the National Center for Atmospheric Research community climate model using observations from the Earth Radiation Budget Experiment
Authors: Soden B. J.
Published: February 2012

Satellite measurements of the effect of clouds on the top of atmosphere radiative energy budget are used to validate model simulations from the National Center for Atmospheric Research Community Climate Model (NCAR CCM). The ability of the NCAR CCM to reproduce the monthly mean global distribution and temporal variability on both daily and seasonal time scales is assessed. The comparison reveals several deficiencies in the CCM cloud representation. Most notable are the difficulties in properly simulating the effect of clouds on the planetary albedo. This problem arises from discrepancies in the model's portrayal of low‐level cloudiness and leads to significant errors in the absorbed solar radiation simulated by the model. The CCM performs much better in simulating the effect of clouds on the longwave radiation emitted to space, indicating its relative success in capturing the vertical distribution of cloudiness. The daily variability of the radiative effects of clouds in both the shortwave and longwave spectral regions is systematically overestimated. Analysis of the seasonal variations illustrates a distinct lack of coupling in the seasonal changes in the radiative effects of cloudiness between the tropics and mid‐latitudes and between the northern and southern hemisphere. Much of this problem also arises from difficulties in simulating low‐level cloudiness, placing further emphasis on the need for better model parameterizations of boundary layer clouds.
A simple analytical function for bidirectional reflectance
Authors: Ahmad Suraiya P. , Deering Donald W.
Published: February 2012

A simple bidirectional reflectance model based on physical scattering laws is developed to calculate the bidirectional reflectance of a wide variety of surfaces. Chandrasekhar's radiative transfer solution, obtained for the anisotropically scattering semi‐infinite medium, is used to compute the multiplescattered radiances. However, since the radiative transfer solution does not take architectural effects into consideration, we adopt Hapke's (1986) approach and add an empirical term to explain the hot‐spot phenomenon and use Cox and Munk's (1954) formulation to take into account the specular reflection. The physical parameters of the model are retrieved from bidirectional reflectance measurements. For each surface, only one set of model parameters is needed for application to all illumination and viewing geometries. The validity of the model is established by comparing the computed and measured reflectances for sets of viewing and illumination angles that were not included in the inversion algorithm. Good agreement is shown between the model‐computed and the observed reflectances for dense prairie vegetation canopies, a sparse desert scrub community, a plowed agricultural field, and an alkali flat.
Estimation of sensible heat flux from remotely sensed canopy temperatures
Authors: Vining R. C. , Blad B. L.
Published: February 2012

Temperatures of tallgrass prairie vegetation were measured with infrared thermometers (IRT) at different view zenith and azimuth angles. The optimum IRT view zenith angle for estimating sensible heat fluxes (H) was determined by comparing H estimated with eddy correlation and/or Bowen ratio techniques to H calculated by a method suggested by Hatfield et al. (1984). For wind speeds of 5 m s−1 or greater, H estimated with surface temperatures measured at a 0° or 20° view zenith angle gave the best agreement, but for wind speeds of less than 4 m s−1 the best estimate of H was made with surface temperatures measured at a 40° or 60° view zenith angle.
Radiometric determination of water vapor and liquid water and its validation with other techniques
Authors: Peter R. , Kämpfer N.
Published: February 2012

For remote sensing applications in the field of atmospheric physics it is necessary to know the highly variable part of the tropospheric water vapor absorption. With a dual‐channel microwave radiometer, operating at 21.3 and 31.5 GHz, the estimation of the water vapor and liquid water content is possible. The retrieval is performed iteratively with an algorithm using simplified model profiles of the troposphere and a millimeter wave absorption model. This site‐independent profile algorithm changes a model atmosphere until the calculated and measured sky brightness temperatures do agree. Integrated precipitable water vapor (IWV) and integrated liquid water (ILW) are obtained by integrating over the corresponding profiles. By the use of the absorption model sky brightness temperatures, opacities or propagation delays at other frequencies up to 1000 GHz can be calculated. Simulations with a few thousand test profiles showed that the rms error, excluding that of the absorption model, is about 3% for the IWV and between 10% and 20% for the ILW (ILW > 0.1 mm), while for the predicted opacities at 90, 142, and 204 GHz the error ranges between 15% and 25%. The performance of the algorithm and the water vapor radiometer has been checked with independent brightness temperature measurements at 142 and 204 GHz, respectively, IR spectroscopic measurements and radiosonde data. The independent measurements showed all a good agreement with the retrieved quantities of the profile algorithm.
Comparison of general circulation models to Earth Radiation Budget Experiment data: Computation of clear‐sky fluxes
Authors: Cess Robert D. , Potter Gerald L. , Gates W. Lawrence , Morcrette Jean‐Jacques , Corsetti Lisa
Published: February 2012

The recent availability of top‐of‐the‐atmosphere radiometric measurements from the Earth Radiation Budget Experiment provides important opportunities for testing and improving numerical climate models. What is unique about these satellite data is that they provide monthly mean clear‐sky measurements. There is, however, considerable confusion as to evaluating clear‐sky radiative fluxes in climate models in a manner that is consistent with the satellite data processing system. This study provides a clear‐sky flux computation method that serves as an analog to the data processing procedure and so provides a model diagnostic that is consistent with the processed satellite data.
A modeling perspective on cloud radiative forcing
Authors: Potter Gerald L. , Slingo Julia M. , Morcrette Jean‐Jacques , Corsetti Lisa
Published: February 2012

Radiation fields from a perpetual July integration of a T106 version of the ECMWF operational model are used to identify the most appropriate way to diagnose cloud radiative forcing in a general circulation model, for the purposes of intercomparison between models. Differences between the methods 1 and 2 of Cess and Potter (1987) and a variant method are addressed. Method 1 is shown to be the least robust of all methods, due to the potential uncertainties related to persistent cloudiness, length of the sampling period, and biases in retrieved clear sky quantities due to insufficient sampling of the diurnal cycle. Method 2 is proposed as an unambiguous way to produce consistent radiative diagnostics for intercomparing model results. The impact of the three methods on the derived sensitivities and cloud feedbacks following an imposed change in sea surface temperature is discussed. The sensitivity of the results to horizontal resolution is considered by using the diagnostics from parallel integrations with T21 version of the model.
Trace gas concentrations and meteorology in rural Virginia: 2. Reactive nitrogen compounds
Authors: Doddridge Bruce G. , Dickerson Russell R. , Wardell R. Glenn , Civerolo Kevin L. , Nunnermacker Linda J.
Published: February 2012

In this second of a two‐part paper on the air chemistry of the Big Meadows site in Shenandoah National Park, Virginia, we present measurements of reactive nitrogen compounds that play important roles in atmospheric photochemistry and acidity, and as nutrients in soil and water. These compounds are, however, poorly understood in terms of spatial and temporal variability. Measurements of nitric oxide, NO, and total reactive nitrogen, NOy, were made for over a year during 1988 and 1989 at a mountain site that we feel is representative of the regional tropospheric composition. We also measured total nitrate (HNO3 + NO3−) for three weeks during this period. For the whole year, the mean, standard deviation, (and median) NOy and daytime NO mixing ratios were 5.1±3.1 (4.3) ppbv and 0.59±0.94 (0.23) ppbv, respectively. A histogram for NOy appears to conform to a lognormal distribution, but fails a χ2 test of significance at the 0.05 level. The speciation of NOy indicates considerable photochemical aging, except in winter. Over the year during daylight, the median ratio NO/NOy was 0.06. Total nitrate (measured in August and September) accounted for 39% of the total NOy. Total reactive nitrogen shows no appreciable diurnal cycle, but NO, NOy, and the ratio NO/NOy show a summer minimum. For winter, spring, summer, and fall, the mean (and median) NOy mixing ratios were: 5.7±3.3 (5.0), 5.4±3.2 (4.4), 4.0±2.1 (3.5), and 5.2±3.2 (4.4) ppbv, respectively. Similarly, seasonally averaged daytime NO values were: 0.95±1.07 (0.61), 0.66±0.93 (0.28), 0.18±0.29 (0.13), and 0.70±1.10 (0.30) ppbv. Wet deposition of nitrate shows the opposite seasonality; we estimate the lifetime of NOy with respect to wet deposition to be 2.7 days in summer and 5.8 days in winter. Ozone and NOy were positively correlated in the summer and negatively correlated in the winter. Carbon monoxide and NOy were positively correlated in all seasons. The slope of a scatter plot of CO vs. NOy, 4.85, provides a lower limit to the molar emissions ratio of CO and NOx. Emissions inventories give a ratio of 4.15.
Relation between electrical conductivity and small ions in the presence of intermediate and large ions in the lower atmosphere
Authors: Dhanorkar Savita , Kamra A. K.
Published: February 2012

Simultaneous measurements of small‐, intermediate‐, and large‐ion concentrations along with those of electrical conductivity, made at Pune (18° 32'N, 73° 51'E, 559 m above mean sea level), India, show that their diurnal variations have maxima in the morning. However, the difference in times of occurrence of the maxima of the polar conductivity and various ion concentrations indicates that all ions of different categories may contribute to polar conductivity in varying degrees. To assess the degree of contribution of individual ion category to the polar conductivity, the data are divided into four different cases. A good linear correlation is observed between electrical conductivity and small‐ion concentration at nighttime in case I when the intermediate‐ and large‐ion concentrations are not very large. However, in other cases when intermediate‐ and/or large‐ion concentrations are more than 2 and 4 orders of magnitude larger than small‐ion concentration, respectively, the correlation between electrical conductivity and small‐ion concentration decreases. A marked improvement in this correlation is observed when the number of small ions, equivalent to the intermediate‐ion and/or large‐ion concentration which gives the same value of electrical conductivity, is added to the small‐ion concentration. The number of small ions equivalent to intermediate‐ion (large‐ion) concentration in different cases is calculated by dividing the intermediate‐ion (large‐ion) concentration by the ratio of the small‐ to intermediate‐ion (large‐ion) mobilities which is approximately equal to 102 (104). Observations show that at certain times of the day intermediate and/or large ions can contribute significantly to electrical conductivity of the air. Therefore at such times, the small‐ion concentration may not be a good indicator of conductivity. The results imply that the contributions of intermediate and large ions can be significant and must be taken into account to get the true conductivity of the air in polluted regions, if one is using ion concentration measurements to estimate the conductivity.
The effects of sampling frequency on the climate statistics of the European Centre for Medium‐Range Weather Forecasts
Authors: Phillips Thomas J. , Gates W. Lawrence , Arpe Klaus
Published: February 2012

The effects of sampling frequency on the first‐ and second‐moment statistics of selected European Centre for Medium‐Range Weather Forecasts (ECMWF) model variables are investigated in a simulation of “perpetual July” with a diurnal cycle included and with surface and atmospheric fields saved at hourly intervals. The shortest characteristic time scales (as determined by the e‐folding time of lagged autocorrelation functions) are those of ground heat fluxes and temperatures, precipitation and runoff, convective processes, cloud properties, and atmospheric vertical motion, while the longest time scales are exhibited by soil temperature and moisture, surface pressure, and atmospheric specific humidity, temperature, and wind. The time scales of surface heat and momentum fluxes and of convective processes are substantially shorter over land than over oceans. An appropriate sampling frequency for each model variable is obtained by comparing the estimates of first‐ and second‐moment statistics determined at intervals ranging from 2 to 24 hours with the “best” estimates obtained from hourly sampling. Relatively accurate estimation of first‐ and second‐moment climate statistics (10% errors in means, 20% errors in variances) can be achieved by sampling a model variable at intervals that usually are longer than the bandwidth of its time series but that often are shorter than its characteristic time scale. For the surface variables, sampling at intervals that are nonintegral divisors of a 24‐hour day yields relatively more accurate time‐mean statistics because of a reduction in errors associated with aliasing of the diurnal cycle and higher‐frequency harmonics. The superior estimates of first‐moment statistics are accompanied by inferior estimates of the variance of the daily means due to the presence of systematic biases, but these probably can be avoided by defining a different measure of low‐frequency variability. Estimates of the intradiurnal variance of accumulated precipitation and surface runoff also are strongly impacted by the length of the storage interval. In light of these results, several alternative strategies for storage of the EMWF model variables are recommended.
Clustering, randomness, and regularity in cloud fields: 2. Cumulus cloud fields
Authors: Zhu T. , Lee J. , Weger R. C. , Welch R. M.
Published: February 2012

During the last decade a major controversy has been brewing concerning the proper characterization of cumulus convection. The prevailing view has been that cumulus clouds form in clusters, in which cloud spacing is closer than that found for the overall cloud field and which maintains its identity over many cloud lifetimes. This “mutual protection hypothesis” of Randall and Huffman (1980) has been challenged by the “inhibition hypothesis” of Ramirez et al. (1990) which strongly suggests that the spatial distribution of cumuli must tend toward a regular distribution. A dilemma has resulted because observations have been reported to support both hypotheses. The present work reports a detailed analysis of cumulus cloud field spatial distributions based upon Landsat, Advanced Very High Resolution Radiometer, and Skylab data. Both nearest‐neighbor and point‐to‐cloud cumulative distribution function statistics are investigated. The results show unequivocally that when both large and small clouds are included in the cloud field distribution, the cloud field always has a strong clustering signal. The strength of clustering is largest at cloud diameters of about 200–300 m, diminishing with increasing cloud diameter. In many cases, clusters of small clouds are found which are not closely associated with large clouds. As the small clouds are eliminated from consideration, the cloud field typically tends towards regularity. Thus it would appear that the “inhibition hypothesis” of Ramirez and Bras (1990) has been verified for the large clouds. However, these results are based upon the analysis of point processes. A more exact analysis also is made which takes into account the cloud size distributions. Since distinct clouds are by definition nonoverlapping, cloud size effects place a restriction upon the possible locations of clouds in the cloud field. The net effect of this analysis is that the large clouds appear to be randomly distributed, with only weak tendencies towards regularity. For clouds less than 1 km in diameter, the average nearest‐neighbor distance is equal to 3–7 cloud diameters. For larger clouds, the ratio of cloud nearest‐neighbor distance to cloud diameter increases sharply with increasing cloud diameter. This demonstrates that large clouds inhibit the growth of other large clouds in their vicinity. Nevertheless, this leads to random distributions of large clouds, not regularity.
Analysis of the upper atmosphere CO2(v2) vibrational temperatures retrieved from ATMOS/Spacelab 3 observations
Authors: López‐Puertas M. , López‐Valverde M. A. , Rinsland Curtis P. , Gunson M. R.
Published: February 2012

An analysis of the upper atmospheric (80–116 km) CO2(v2) vibrational temperatures retrieved from atmospheric trace molecule spectroscopy (ATMOS) experiment Spacelab 3 spectra by using a nonlocal thermodynamic equilibrium (non‐LTE) radiative transfer model is presented. Thermal collisions with atmospheric atomic oxygen keep this vibrational state very close to LTE up to around 100 km. Above this height the different deviations from LTE retrieved from ATMOS/Spacelab 3 spectra for the northern and southern hemispheres are explained in terms of this collisional process and in terms of the different kinetic temperature profiles measured at those locations. From these simultaneous observations of the kinetic and CO2(v2) vibrational temperatures a deactivation rate of CO2(v2) by O(3P) has been derived which, considering the available climatologies of the concentration of this compound, leads to a rate coefficient value between 3 and 6 × 10−12 cm3 s−1 and favors an independent or negative temperature dependence rate constant for the atmospheric temperature range. Cooling rates induced by the CO2 15‐μm fundamental band in the upper mesosphere and lower thermosphere (80–116 km) were derived from the simultaneous kinetic temperature, CO2(v2) vibrational temperature, and CO2 concentration, as measured by ATMOS/Spacelab 3, and found to be a factor of between 5 and 10 times larger than those generally accepted until very recently.
Diagnostic model study of the seasonal variation of global ozone and the Antarctic ozone hole
Authors: Akiyoshi H. , Uryu M.
Published: February 2012

A simple two‐dimensional model is constructed to simulate and gain an understanding of the global distribution of ozone and its seasonal variation. In the model the Chapman cycle parameterized by Hartmann (1978) is used. The time dependence of the diffusion coefficients is neglected, except in the polar regions. The effects of the meridional circulation, consisting of the following three components, are taken into account: (1) an annually varying component due to the annual variation in the heating of ozone, oxygen, and water vapor, which is assumed to be anti‐symmetric (symmetric with a 6 month shift) about the equator; (2) a nonseasonal, steady component of the transport circulation with ascending air in the tropics and descending air in the middle and high latitudes of both hemispheres; and (3) an annually varying component of the transport circulation which represents planetary wave activity, strong convection in the tropics, and other seasonally variable factors. Although the employed circulations and diffusion coefficients are ad hoc, the simple model simulates the main features of the global distribution of ozone and its seasonal variation. The Antarctic ozone hole is discussed from a global point of view. The possibility of a weak October minimum in the Antarctic total ozone amount, without introducing chlorine chemistry, is suggested.
New particle formation in the marine boundary layer
Authors: Covert David S. , Kapustin Vladimir N. , Quinn Patricia K. , Bates Timothy S.
Published: February 2012

Aerosol measurements were made in the marine boundary layer along the coast of Washington State during the Pacific Stratus Sulfur Investigation. On April 22 the particle concentration increased to levels much higher than usual for the clean marine boundary layer. The total particulate number concentration greater than 3 nm diameter increased rapidly from about 250 cm−3 to 3200 cm−3, remained near that level for 7 hours, and then decreased over the next 2 hours to less than 400 cm−3. The change could not be attributed to either local or distant contamination. Immediately before the increase particulate surface area concentration dropped from 25 μm2 cm−3 to less than 5 μm2 cm−3. The SO2 concentration increased from about 20 pptv to 40–60 pptv just before the increase in particle concentration. While these measurements cannot distinguish between changes in number concentration caused by particle nucleation versus advection or vertical mixing, clearly there was recent or continuing particle production on a mesoscale in the air mass. Related aircraft measurements and model results support the hypothesis of new particle formation. These data provide evidence that at times high concentrations of new, ultrafine particles are formed at low SO2 concentrations under marine conditions. This homogeneous nucleation, as opposed to heterogeneous condensation on existing particles, is strongly and inversely dependent on the concentration of existing particles.
Surface reflectance retrieval from satellite and aircraft sensors: Results of sensor and algorithm comparisons during FIFE
Authors: Markham B. L. , Halthore R. N. , Goetz S. J.
Published: February 2012

Visible to shortwave infrared radiometric data collected by a number of remote sensing instruments on aircraft and satellite platforms were compared over common areas in the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) site on August 4, 1989, to assess their radiometric consistency and the adequacy of atmospheric correction algorithms. The instruments in the study included the Landsat 5 thematic mapper (TM), the SPOT 1 high‐resolution visible (HRV) 1 sensor, the NS001 thematic mapper simulator, and the modular multispectral radiometers (MMRs). Atmospheric correction routines analyzed were an algorithm developed for FIFE, LOWTRAN 7, and 5S. A comparison between corresponding bands of the SPOT 1 HRV 1 and the Landsat 5 TM sensors indicated that the two instruments were radiometrically consistent to within about 5%. Retrieved surface reflectance factors using the FIFE algorithm over one site under clear atmospheric conditions indicated a capability to determine near‐nadir surface reflectance factors to within about 0.01 at a reflectance of 0.06 in the visible (0.4–0.7 μm) and about 0.30 in the near infrared (0.7–1.2 μm) for all but the NS001 sensor. All three atmospheric correction procedures produced absolute reflectances to within 0.005 in the visible and near infrared. In the shortwave infrared (1.2–2.5 μm) region the three algorithms differed in the retrieved surface reflectances primarily owing to differences in predicted gaseous absorption. Although uncertainties in the measured surface reflectance in the shortwave infrared precluded definitive results, the 5S code appeared to predict gaseous transmission marginally more accurately than LOWTRAN 7.
Stratospheric minor constituent distributions from far‐infrared thermal emission spectra
Authors: Abbas Mian M. , Traub Wesley A.
Published: February 2012

We retrieve mixing ratio profiles of O3, H216O, H217O, H218O, HF, and HCl from far‐infrared thermal emission observations of the limb in the 80–220 cm−1 spectral region. The observations were made with a balloon‐borne Fourier transform spectrometer as a part of the 1983 Balloon Intercomparison Campaign (BIC‐2). A subset of the data was analyzed previously using the method in the work of Traub et al. [1982, 1991]; in the present paper we use an alternative method of calibration and analysis, given by Abbas et al. [1985]. The retrieved constituent profiles are compared with the measurements made with other instruments on the BIC‐2 flights. The results for the concentrations of H217O and H218O obtained in this study indicate no isotopic enhancement or depletion with a standard deviation of about 20%.