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In their recent paper, Grandin et al. (2014) claim to have developed a novel approach, principally a ray tracing method, to analyze radio sounding data from occulted spacecraft signals by planetary atmospheres without the usual assumptions of the radio occultation inversion method of a stratified, layered, symmetric atmosphere. They apply their " new approach" to observations of the Mars Express Radio Science (MaRS) experiment and compare their resulting temperature, neutral number density and electron density profiles with those from MaRS, claiming that there is good agreement with the observations. The fact is, however, that there are serious disagreements in the most important altitude ranges. Their temperature profile shows a 30 K shift or a 300σ (1σ standard deviation = 0.1 K for the MaRS profile near the surface) difference towards warmer temperatures at the surface when compared with MaRS while the MaRS profile is in best agreement with the profile from the Mars Climate Data Base V5.0 (MCD V5.0). Their full temperature profile from the surface to 250 km altitude deviates significantly from the MCD V5.0 profile. Their ionospheric electron density profile is considerably different from that derived from the MaRs observations. Although Grandin et al. (2014) claim to derive the neutral number density and temperature profiles above 200 km, including the asymptotic exosphere temperature, it is simply not possible to derive this information from what is essentially noise.

Systematic measurements of isotopic tracers in the atmosphere, particularly tritium, deuterium, and oxygen 18 in water vapor, are for practical reasons largely restricted to samples obtained at ground level. On the other hand, their use as atmospheric tracers requires as complete a knowledge as possible of their sources and sinks as well as of their distribution and transport patterns (in space and time) in the atmosphere. In their paper, Schell et al. [1970] attempt to develop a model that permits combination of isotope measurements in ground-level samples with meteorological parameters of the three-dimensional atmosphere in order to calculate the desired tracer distribution and transport values. In this particular case, the authors determine the tracer injection into the moist tropospheric layer (surface to 500 mb) from above.

The Generic Screening Object hypothesis of Frank et al. (1986) is refuted, and it is indicated that the DE-1 dark pixel events do not serve as evidence for a large cometary influx. It is shown that the average scan line count profiles of the dark pixel events show no significant reductions in the two neighboring pixel positions, although at least a 9 percent reduction would be expected if the dark pixels were the result of shielding of the photometric field of view. In a reply, Frank et al. uphold their previous hypothesis, pointing out that the suggestion that the atmospheric holes are not a geophysical phenomenon is incorrect due to: (1) the use of an overly simplified model for the instrument responses to small, opaque objects as seen against a statistically fluctuating screen of dayglow intensities; and (2) an insufficient treatment of the observations.

The observations of transient decreases or holes in the EUV dayglow reported by Frank et al. (1986) and attributed to an influx of small comets into the earth atmosphere are discussed critically. The techniques used in acquiring and analyzing the observational data are examined, and it is argued that the decreases are probably instrument artifacts. A critique of the geophysical basis of the comet hypothesis is also included. In a reply by Frank et al., the instrument-artifact argument is rejected, in part on the basis of the statistical properties of the holes observed. Additional observational data are presented in graphs and dynamics Explorer 1 images are analyzed in detail.

The proposal by Frank et al. (1986) that clouds of small comets periodically inject large amounts of H2O into the upper atmospheres of the earth, Venus, and Mars is examined critically, with a focus on transport and disposal mechanisms invoked to account for the large H2O masses involved. It is argued that observed parameter values (such as mixing ratios, vertical wind velocities, and H escape flows) prohibit transport by eddy, molecular diffusion, vertical avection, or coherent movement. In a reply by Frank et al., these objections are discussed in terms of an overall description of the decelerataion and penetration of a cometary water cloud, and H2O concentrations and mixing mechanisms consistent with observed values for the earth are proposed. It is suggested that an increase in cometary H2O influx could lead to concentrations attaining the frost point and to formation of a global mesospheric cloud with significant climate effects. A lower H2O influx rate for Venus (consistent with observed H loss and atmospheric H2O concentration) and relatively rapid loading of the Mars surface and atmosphere with H2O ice and vapor (followed by brief warming periods with increased exospheric H2O outflow and surface flow of liquid H2O) are considered.

A critique is presented of an analysis by Penn and Martell (J. Geophys. Res., 68: 4195-207(1963)), in which it was concluded that practically all the fallout in the southeastern U. S. in late Sept. 1961 resulted from radioactivity vented to the atmosphere from an underground nuclear test at the Nevada Test Site on Sept. 15, 1961. A reply to the critique is also included. (T.F.H.)

The possibility that comets containing up to 100 tons of ice encounter the earth's atmosphere at a rate of one every 20 min is discussed. Cometary 'hail storms' were proposed to explain observed regular transient decreases in the atmospheric UV dayglow intensity. The decreases take the form of dark 'holes' up to 50 km across. The probability that clouds of objects assumed to be as dark as the nucleus of Comet Halley between the earth and moon would be detectable by ground-based electrooptical deep space telescopes is considered. Conflicting projections of the number of objects which would be detected per hour are examined. High correlations are noted between cometary passages (Comets Encke, Tuttle, Tempel) and intervals of meteor showers (Taurids, Leonids, Geminis, etc.). The holes, however, are not correlated or coincident with the showers. It is suggested that dedicated searches for the unclassified dark objects be carried out in November, when cometary fluxes are high.

Frank et al. (1986) argue that, on the basis of dayglow observations, about 20 small comets of mass roughly 100,000 g hit the earth each minute. The proposed comets appear to require dust mantles; for otherwise they would evaporate quickly and contribute to the solar wind. Such an enrichment is not observed. An order-of-magnitude argument based on comet sizes, densities, and meteoritic dust influx is used here to show that the dust mantles can have a maximum thickness of about 200 microns. A reasonable estimate gives a thickness of about 0.2 micron. The mantles are thus too thin to suppress evaporation.

(1) Introduction—In a short paper published in this Journal in December, 1946, I gave the results of 12,330 measurements of height of polar aurora observed in Southern Norway during 1911–44. The present paper deals with the statistical work undertaken since that publication. If we compare the diagram of height (Fig. 1) in the above-mentioned paper with the corresponding one from my expedition to Northern Norway in 1913 [see 1 of “References” at end of this paper], one of the essential differences is that the aurora in Southern Norway occur at much greater heights than those in Northern Norway. There are two reasons for this. First, certain aurora occurring in the Earth's shadow during years of great solar activity as rays and red diffuse surfaces [2], often reach great heights (from 300 to 700 km) and are seldom observed in Northern Norway. Second, the auroral rays in that part of the atmosphere lying in sunshine—which have only once been measured in Northern Norway [3]—have a position very much higher than aurora in shadow, as already pointed out in my paper on sunlit auroral rays published in 1929 [4]. This difference is clearly seen in Figure 1, where the 12,330 heights from my first paper of 1946 are split into heights of aurora in shadow (left) and aurora partly or completely in sunlight (right) [5]. For each kilometer the measured heights are distributed as points along the corresponding horizontal line at approximately equal distances. The same remark applies to the other Figures in this paper.

In this paper we use the Mars implementation of the Planet Weather Research and Forecasting model, MarsWRF, to simulate the Entry, Descent and Landing (EDL) vertical profiles from six past missions: Pathfinder, Mars Exploration Rovers Opportunity and Spirit, Phoenix, Mars Science Laboratory Curiosity rover, and ExoMars 2016 (Schiaparelli), and compare the results with observed data. In order to investigate the sensitivity of the model predictions to the atmospheric dust distribution, MarsWRF is run with two prescribed dust scenarios. It is concluded that the MarsWRF EDL predictions can be used for guidance into the design and planning stage of future missions to the planet, as it generally captures the observed EDL profiles, although it has a tendency to underestimate the temperature and overestimate the density for heights above 15 km. This could be attributed to an incorrect representation of the observed dust loading. We have used the model to predict the EDL conditions that may be encountered by two future missions: ExoMars 2020 and Mars 2020. When run for Oxia Planum and Jezero Crater for the expected landing time, MarsWRF predicts a large sensitivity to the dust loading in particular for the horizontal wind speed above 10-15 km with maximum differences of up to ±30 m/s for the former and ±15 m/s for the latter site. For both sites, the best time for EDL, that is, when the wind speed is generally the weakest with smaller shifts in direction, is predicted to be in the late morning and early afternoon., We are grateful to the National Aeronautics and Space Administration (NASA) for making the EDL vertical profiles of past Mars missions available online through the Planetary Atmospheres Node of the PDS (http://pds‐atmospheres.nmsu.edu/). Alessio Aboudan from the University of Padova is also acknowledged for providing the reconstructed vertical profiles for the Schiaparelli EDL. The simulations presented in this paper were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the High Performance Computing Center North (HPC2N) Abisko cluster. This work was partially funded by the European Research Foundation (ERF). We would like to thank an anonymous reviewer and Claire Newman for their many detailed and insightful comments and suggestions that helped to improve significantly the quality of the paper. The model data used to generate the figures presented in this paper can be obtained from the authors. We have uploaded the data to the following website (https://atmospheres.research.ltu.se/owncloud/index.php/s/PlZWyxd1T24vl16).

A VHF radar has been established at a site near Resolute Bay in Nunavut, Canada (75°N, 95°W), which has the capability to make a variety of measurements relating to the atmospheric and ionospheric environment in the polar regions. The site is very close to the north geomagnetic pole, and therefore the radar is well situated to make some unique measurements. The system is a multipurpose instrument with good remote control capabilities. It can be used as a wind profiler radar to study the lower troposphere, as a mesospheric radar to study polar mesosphere summer echoes (PMSE) in summer, as a meteor radar to determine winds in the altitude region of 80–100 km, and as an ionospheric radar to study 3 m scale irregularities in the E and F regions. The radar has some unique design features, partly dictated by the rough terrain in which it is sited. In this paper, the radar system is described, including description of some unusual approaches to deal with special conditions at the site, and then some key early results are presented. Important findings include error determinations for tropospheric wind measurements, detection of PMSE, correlations between PMSE and atmospheric temperatures at 86 km altitude, measurements of mean winds and tidal characteristics over a full year, and detection of various normal modes of oscillation in the 80–100 km region, especially in nonsummer months. Some of these features will be discussed here, but more detailed discussions will be left to related papers in this issue.

Land surface albedo constitutes a critical climatic variable, since it largely controls the actual amount of solar energy available to the Earth system. The purpose of this paper is to establish a theory for the exploitation of space observations to solve the atmosphere/surface radiation transfer problem on an operational basis and to generate surface albedo, aerosol load, and possibly land cover change products. Surface albedo is rather variable in space and time and depends both on the structure and on the radiative characteristics of the surface, as well as on the angular and spectral distribution of radiation at the bottom of the atmosphere. Weather and climate models often use preset distributions or simple parameterizations of this environment variable, even though such approaches do not accurately account for the actual effect of the underlying surface. From a mathematical point of view, the determination of the surface albedo corresponds to the estimation of a boundary condition for the radiation transfer problem in the coupled surface-atmosphere system. A relatively large database of 10 years or more of Meteosat data has been accumulated by EUMETSAT. These data, collected at half-hour intervals over the entire Earth disk visible from longitude 0°, constitute a unique resource to describe the anisotropy of the coupled surface-atmosphere system and provide the opportunity to document changes in surface albedo which may have occurred in these regions over that period. In addition, since the coupled surface-atmosphere radiation transfer problem must be solved, the proposed procedure also yields an estimate of the spatial and temporal distribution of aerosols. The proposed inversion procedure yields a characterization of surface radiative properties that may also be used to document and monitor land surface dynamics over the portion of the globe observed by Meteosat. Results from preliminary applications and an error budget analysis are discussed in a companion paper [Pinty et al., this issue].

This paper analyzes data obtained on July 3 and 18, 1995, during the summer 1995 Southern Oxidant Study (SOS) field campaign. In a previous paper (Nunnermacker et al., 1998) we analyzed measurements of key species that contribute to formation of O3 in the Nashville urban plume and presented a semiquantitative picture of O3 production in the plume from the point of emission to locations where no net O3 was being formed. In this paper we use a box model constrained by observed concentrations of stable species to obtain a detailed mechanistic description of the instantaneous processing of urban emissions at various times in the chemical evolution of the urban plume. Instantaneous ozone production rates and efficiencies with respect to NOx and to primary radical production are examined. At high NOx concentrations in the fresh urban plume the O3 production rate was found to be directly proportional to the hydrocarbon to NOx reactivity ratio. At lower NOx concentrations, corresponding to the mature urban plume and the background atmosphere, the O3 production rate was found to be directly proportional to the NOx concentration and independent of the hydrocarbon reactivity. NOx was found to be most efficiently used for ozone production at low NOx concentrations. In contrast, the efficiency with which the system uses primary radicals was found to be very low at low NOx concentrations and to peak at a NOx concentration of approximately 4 ppbv. A sensitivity study of the instantaneous O3 production rates to changes in NOx or hydrocarbon concentrations showed that the instantaneous 03 production rate at the center of the urban plume, when half of the urban NOx emissions had been processed, is hydrocarbon sensitive. However, 03 production becomes NOx sensitive as the plume matures.

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment aboard the Shuttle Pallet Satellite (SPAS) was successfully flown in early November 1994 (STS 66) and in August 1997 (STS 85). This paper focuses on the first flight of the instrument, which was part of the Atmospheric Laboratory for Application and Science 3 (ATLAS 3) mission of NASA. During a free flying period of 7 days, limb scan measurements of atmospheric infrared emissions were performed in the 4 to 71 μm wavelength region. For improved horizontal resolution, three telescopes (viewing directions) were used that sensed the atmosphere simultaneously. Atmospheric pressures, temperatures, and volume mixing ratios of various trace gases were retrieved from the radiance data by using a fast onion-peeling retrieval technique. This paper gives an overview of the data system including the raw data processing and the temperature and trace gas profile retrieval. Examples of version 1 limb radiance data (level 1 product) and version 1 mixing ratios (level 2 product) of ozone, ClONO 2 , and CFC-11 are given. A number of important atmospheric transport processes can already be identified in the level 1 limb radiance data. Radiance data of the lower stratosphere (18 km) indicate strong upwelling in some equatorial regions, centered around the Amazon, Congo, and Indonesia. Respective data at the date line are consistent with convection patterns associated with El Nino. Very low CFC-11 mixing ratios occur inside the South Polar vortex and cause low radiance values in a spectral region sensitive to CFC-11 emissions. These low values are a result of considerable downward transport of CFC-11 poor air that occurred during the winter months. Limb radiance profiles and retrieved mixing ratio profiles of CFC-11 indicate downward transport over ∼5 km. The accuracy of the retrieved version 1 mixing ratios is rather different for the various trace gases. In the middle atmosphere the estimated systematic error of ozone is ∼14%. Ozone data of correlative satellite measurements are well within this error bar. CRISTA agrees, for example, with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) sunset measurements typically within 5%. The random error of version 1 ozone mixing ratios is 4%. Similar values apply to other trace gases. These low random errors allow the identification of small and medium scale horizontal and vertical structures in the measured trace gas distributions. Examples of structures in mixing ratio fields of ozone, ClONO 2 , and CFC-11 are given.

This is the second in a series of two papers on thermal inertia estimation from satellite data. In this paper we present the methodology that permits thermal inertia mapping using NOAA-advanced very high resolution radiometer data from the four temperatures algorithm developed in the first paper. Four NOAA images are used to assess thermal inertia: an image at 14:30 (nominal hour) is used to estimate the surface albedo; others at 2:30 and 14:30 are used to estimate the diurnal surface temperature range, while images at 7:30, 14:30, and 19:30 are used to assess the phase difference. The main advantage of the methodology is that the phase difference is obtained from satellite data without the need to know the value of the effective surface emissivity and total water vapor content of the atmosphere. Following the proposed algorithm and the developed methodology, maps of thermal inertia are presented, two for the Iberian Peninsula (on two consecutive days to check consistency of the results) and one for Morocco (to check behavior in different landscapes). The thermal inertia values obtained are consistent with the known properties of these zones.

Tentative estimates, using three-dimensional chemistry and transport models, have suggested small ozone increases in the upper troposphere resulting from current aircraft emissions, but have also concluded to significant deficiencies in today's models and to the need to improve them through comparison with extended data sets. The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program was initiated in 1993 by European scientists, aircraft manufacturers, and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapor by five long range passenger airliners flying all over the world. The aim is not to detect direct effects of aircraft emissions on the ozone budget inside the air traffic corridors but to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapor climatologies at 9–12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g., radiatively and stratosphere/troposphere exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occuring in the upper troposphere and the lowermost stratosphere, and the model treatment of near tropopause chemistry and transport. During MOZAIC I (January 1993–September 1996), fully automatic devices were developed, installed aboard five commercial Airbus A340s, and flown in normal airline service. A second phase, MOZAIC II, started in October 1996 with the aim of continuing the O3 and H2O measurements and doing a feasibility study of new airborne devices (CO, NOy). Between September 1994 and December 1997, 7500 flights, representing 54,000 flight hours, were made over the continents (Europe, North America, Asia, South America, and Africa) and the Atlantic Ocean. Most of the measurements (90%) correspond to cruise altitudes (9–12 km), the remaining being obtained during ascents and descents near the 50 cities frequented by MOZAIC operations. This paper reports the main characteristics of the program and the flights, with a brief summary of the general content and focus of papers already published and companion papers of this special issue. These deal with the following: description and validation of the ozone and water vapor measurement methods; presentation of an accurate ozone climatology at 9–12 km altitude, over the Northern Hemisphere (130°W–140°E; 0°–80°N), and down to 30°S over South America and Africa; comparison between a 2-year MOZAIC ozone climatology (1994–1996; 0–12 km) and a long series of older measurements made since the 1980s at 8 stations of the Ozone Sounding Network; study of ozone-rich transients, up to 500 ppbv on a horizontal scale of 5–80 km, in the upper tropical troposphere; and comparison between MOZAIC ozone data and output from the global chemistry and transport model (CTM) TOMCAT.

This paper is an introduction to and overview of the accompanying papers in this issue which give detailed results from the Galileo probe mission to Jupiter, including results from the Galileo orbiter and Earth-based observations that are relevant for understanding the probe data and placing them in context. A summary of prior knowledge of Jupiter's atmosphere is also presented. All probe scientific investigations were successful. As anticipated, the Galileo probe results confirm some expectations about Jupiter, refute others, and raise important new questions. The Galileo probe defined the atmospheric thermal structure at the probe entry site from ∼1000 km above the 1 bar pressure level to a depth near 22 bars. During direct atmospheric sampling beginning near 0.4 bar, instruments on the probe measured composition, cloud properties, thermal structure, winds, radiative energy balance, and electrical properties of the Jovian atmosphere. Prior to reaching the Jovian atmosphere, probe instruments measured properties of the inner magnetosphere, observing regions not previously sampled by any spacecraft.

Data assimilation is a vital technique in modern meteorology, allowing information from a wide range of observations to be combined to produce synoptic analyses of the atmospheric circulation. Data assimilation has a number of advantages over conventional analysis methods that stem from the use of a numerical model of the atmosphere as an integral part of the technique. The model provides a framework which allows information from observations to be combined with our understanding of the atmosphere, as embodied in the model, so that a consistent, evolving, three-dimensional picture of the atmospheric circulation may be constructed. The aim of this paper is to compare results from two different stratospheric data assimilation systems (from Goddard Space Flight Center and the U.K. Meteorological Office) to assess the reliability of analyses derived by using assimilation techniques. In particular, this paper concentrates on assessing the quality of the analyses for long-term transport studies. First, the zonal mean circulations are compared, with emphasis on the consistency of the residual circulation. Second, horizontal transport processes are compared, with particular emphasis on the representation of features in the neighborhood of the wintertime polar vortex. It is shown that the two analyses give a broadly consistent picture of the atmospheric circulation. Where differences are identified, they can often be attributed to particular shortcomings in one of the assimilation systems. The results presented here stress the usefulness of data assimilation for stratospheric studies.

This paper presents the description of the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) rain rate database and its different spatial and temporal variability characteristics. Accuracy and reliability of this database are evaluated with the position of the appropriateness of its use for the practical (ground truth, beam filling error for the Tropical Rainfall Measuring Mission) and theoretical (spectral estimation) problems. The following is shown in this paper: the concentration of a significant power in the origin of the frequency axis in the temporal spectra; the existence of a diurnal cycle (which has a range of variation of about 1.43 to 2.03 mm/h); the distinction between the north-south and east-west transport of rain, reflected in the two-dimensional spectrum and correlation function of the spatial field, and character of its anisotropy; the scales of the differences between the corresponding estimates of the TOGA and Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) data. The documentation of the TOGA COARE database is given. Methodology and software (in IDL and Fortran languages) for management of the TOGA COARE database system and for estimating of different variability statistics were developed. The results obtained can be used for choosing any subset appropriate for the particular rain analysis study, for rain modeling, for comparison with corresponding estimates of other sources of data (satellite or simulated by physical models), and for solving some other scientific and engineering problems connected with rain measurements and modeling.

An extensive study of tropospheric photochemical trace species, including the hydroxyl radical OH was conducted in the Colorado Rocky Mountains from early August to early October 1993. Many of the parameters that influence the abundance of OH in the atmosphere, including j(O3 and NO2), formaldehyde, nonmethane hydrocarbons, NOx, ozone, H2O, aerosols, and others, were measured simultaneously with OH. Instrumentation for measurement of OH included a long-path spectroscopic technique and several in situ techniques: ion-assisted mass spectrometry, laser-induced resonance fluorescence, and a liquid scrubber/liquid chromatographic method. Instrument comparisons between long-path and in situ measurements were conducted for OH, O3, CH2O, NO2, and H2O, and these measurements provide a valuable insight into the chemistry of the region. The complete data set provided a robust set of inputs to a zero-dimensional model for exploring OH photochemistry. Independently measured OH concentrations were in agreement within one standard error much of the time, thus giving confidence that hydroxyl is being measured correctly. OH concentrations were typically low during clean continental airflow with concentrations rarely above 4×106 cm−3. During occasions of polluted airflow from the Denver-Boulder metropolitan areas, values of OH rose as high as 1.2×107 cm−3. The nearly complete suite of trace gases measured simultaneously with the hydroxyl radical severely constrained the models and provided numerous opportunities to compare relations between species (e.g. OH versus NOx, OH/HO2, RO2 versus NOx). Modeled hydroxyl results using the complete species suite were about a factor of 1.5 higher than measured OH concentrations suggesting that the photochemistry may not be well understood. The campaign data provide new insights into the chemistry of the lower troposphere. This paper provides an overview of the campaign and brief descriptions of results from individual experiments. Details are provided in the accompanying papers in this issue.

Atmospheric loss from planetary atmo- spheres is an important geophysical problem with impli- cations for planetary evolution. This is a multidisci- plinary research field that requires an expertise in a wide range of subjects including statistical mechanics, fluid mechanics, plasma physics, collision theory, and surface science. This paper is a review of the current state of our understanding of atmospheric loss from the terrestrial planets. A detailed discussion is provided of the basic concepts required to understand the processes occurring in the high-altitude portion of a planetary atmosphere referred to as the exosphere. Light atomic species with sufficient translational energy can escape from an atmo- sphere. The translational energy required for escape could be thermal energy and proportional to the ambi- ent temperature or the result of some collisional pro- cesses energizing the species above thermal energies. These collisional processes, which include charge ex- change and dissociative recombination between ener- getic ions, neutrals, and electrons, are referred to as nonthermal escape processes. We highlight the similar- ities and differences in the important escape mechanisms on the terrestrial planets and comment on application of these mechanisms to evolutionary theories of the terres- trial atmospheres. The emphasis in this paper is directed toward the need to consider the exosphere as collisional.

Small particles in the atmosphere, called "atmospheric aerosol" have a direct effect on Earth climate through scattering and absorbing sunlight, and also an indirect effect by changing the properties of clouds, as they interact with solar radiation as well. Aerosol typically stays in the atmosphere for several days, and can be transported long distances, affecting air quality, visibility, and human health not only near the source, but also far downwind. Smoke from vegetation fires is one of the main sources of atmospheric aerosol; other sources include anthropogenic pollution, dust, and sea salt. Chemistry transport models (CTMs) are among the major tools for studying the atmospheric and climate effects of aerosol. Due to the considerable variation of aerosol concentrations and properties on many temporal and spatial scales, and the complexity of the processes involved, the uncertainties in aerosol effects on climate are large, as is featured in the latest report of Intergovernmental Panel on Climate Change (IPCC) in 2007. Reducing this uncertainty in the models is very important both for predicting future climate scenarios and for regional air quality forecasting and mitigation. During vegetation fires, also called biomass burning (BB) events, complex mixture of gases and particles is emitted. The amount of BB emissions is usually estimated taking into account the intensity and size of the fire and the properties of burning vegetation. These estimates are input into CTMs to simulate BB aerosol. Unfortunately, due to large variability of fire and vegetation properties, the quantity of BB emissions is very difficult to estimate and BB emission inventories provide numbers that can differ by up to the order of magnitude in some regions. Larger uncertainties in data input make uncertainties in model output larger as well. A powerful way to narrow the range of possible model estimates is to compare model output to observations. We use satellite observations of aerosol properties, specifically aerosol optical depth, which is directly proportional to the amount of aerosol in the atmosphere, and compare it to the model output. Assuming the model represents aerosol transport and particle properties correctly, the amount of BB emissions determines the simulated aerosol optical depth. In this study, we explore the regional performance of 13 commonly used emission estimates. These are each input to global Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. We then evaluate how well each emission estimate reproduces the smoke aerosol optical depth measured by the MODIS instrument. We compared GOCART-simulate aerosol optical depth with that measured from the satellite for 124 fire cases around the world during 2006 and 2007. We summarize the regional performance of each emission inventory and discuss reasons for their differences by considering the assumptions made during their development. We also show that because stronger wind disperses smoke plumes more readily, in cases with stronger wind, a larger increase in emission amount is needed to increase aerosol optical depth. In quiet, low-wind-speed environments, BB emissions produce a more significant increase in aerosol optical depth, other things being equal. Using the region-specific, quantitative relationships derived in our paper, together with the wind speed obtained from another source for a given fire case, we can constrain the amount of emission required in the model to reproduce the observations. The results of this paper are useful to the developers of BB emission inventories, as they show the strengths and weaknesses of individual emission inventories in different regions of the globe, and also for modelers who use these inventories and wish to improve their model results.

During the period 1988-1990, studies of atmospheric aerosol have been made over the Atlantic. These include measurement programs out of Ascension Island (8{degrees}S, 14{degrees}W), the Azores (38{degrees}N, 25{degrees}W), Iceland (63{degrees}N, 23{degrees}W), and from the United Kingdom over the Northeast Atlantic. For these studies the equipment deployed included an airborne backscatter lidar (operating at 10.6 {mu}m), airborne particle-sounding probes, ground-based lidars (operating at 10.6, 0.53, and 0.35 {mu}m), balloon radiosondes, and a Sun-tracking photometer. In addition, standard meteorological information has been incorporated along with, when appropriate, data from the SAGE II limb-sounding satellite. The present paper thus introduces an overview of the program together with an outline of the technology, measurement characteristics, and performance of the airborne equipment that determined the strategic planning of much of the work. The measurements themselves, made in the relatively clean period for the atmosphere before the Mount Pinatubo eruption, will be presented in a subsequent series of papers. 26 refs., 5 figs., 3 tabs.

[1] In the companion to the present paper, the one-dimensional k-e lake model SIMSTRAT is coupled to a single-column atmospheric model, nicknamed FIZC, and an application of the coupled model to the deep Lake Geneva, Switzerland, is described. In this paper, the response of Lake Geneva to global warming caused by an increase in atmospheric carbon dioxide concentration (i.e., 2 × CO2) is investigated. Coupling the models allowed for feedbacks between the lake surface and the atmosphere and produced changes in atmospheric moisture and cloud cover that further modified the downward radiation fluxes. The time evolution of atmospheric variables as well as those of the lake's thermal profile could be reproduced realistically by devising a set of adjustable parameters. In a “control” 1 × CO2 climate experiment, the coupled FIZC-SIMSTRAT model demonstrated genuine skills in reproducing epilimnetic and hypolimnetic temperatures, with annual mean errors and standard deviations of 0.25°C ± 0.25°C and 0.3°C ± 0.15°C, respectively. Doubling the CO2 concentration induced an atmospheric warming that impacted the lake's thermal structure, increasing the stability of the water column and extending the stratified period by 3 weeks. Epilimnetic temperatures were seen to increase by 2.6°C to 4.2°C, while hypolimnion temperatures increased by 2.2°C. Climate change modified components of the surface energy budget through changes mainly in air temperature, moisture, and cloud cover. During summer, reduced cloud cover resulted in an increase in the annual net solar radiation budget. A larger water vapor deficit at the air-water interface induced a cooling effect in the lake.

[1] In this paper, the potential of a multifrequency submillimeter radiometer to characterize ash plumes in the near-field of a volcanic eruption is evaluated. The radiometer's sensitivity to mass concentration and particle effective dimension is shown to depend most critically on aerosol altitude and ejected water vapor concentration. There is also some dependence on temperature, aerosol shape and complex refractive index. For this study, the volcanic aerosols are assumed to be randomly oriented solid hexagonal silicates of aspect ratio unity. The T-matrix method is used to calculate the single-scattering properties of the aerosols at 36 frequencies between 90 GHz and 880 GHz, and the aerosol bulk scattering properties are derived assuming lognormal size distribution functions. A midlatitude standard summer atmosphere and a perturbed midlatitude summer atmosphere are used to quantify the sensitivity, using the delta-Eddington two-stream approximation, of the radiometer to the presence of aerosol. It is shown that at 34 frequencies, between 113 GHz and 880 GHz, the sensitivity to aerosol is a maximum if the following four conditions are satisfied: (i) The altitude of the aerosol layer should be ≫ 3 km, (ii) 0.1 g m−3 < mass concentration < 30 g m−3 (iii) the aerosol effective dimension, De, 20 μm < De < 1000 μm and (iv) water vapor ejected by a volcano into the atmosphere should be < 1000 times greater than the background water vapor concentration. The paper demonstrates the potential usefulness of using spectrally resolved submillimeter measurements in the near-field of volcanic eruptions to characterize plume properties.

Aerosols are tiny suspended particles in the atmosphere that scatter and absorb sunlight. Smoke particles are aerosols, as are sea salt, particulate pollution and airborne dust. When you look down at the earth from space sometimes you can see vast palls of whitish smoke or brownish dust being transported by winds. The reason that you can see these aerosols is because they are reflecting incoming sunlight back to the view in space. The reason for the difference in color between the different types of aerosol is that the particles arc also absorbing sunlight at different wavelengths. Dust appears brownish or reddish because it absorbs light in the blue wavelengths and scatters more reddish light to space, Knowing how much light is scattered versus how much is absorbed, and knowin~ that as a function of wavelength is essential to being able to quantify the role aerosols play in the energy balance of the earth and in climate change. It is not easy measuring the absorption properties of aerosols when they are suspended in the atmosphere. People have been doing this one substance at a time in the laboratory, but substances mix when they are in the atmosphere and the net absorption effect of all the particles in a column of air is a goal of remote sensing that has not yet been completely successful. In this paper we use a technique based on observing the point at which aerosols change from brightening the surface beneath to darkening it. If aerosols brighten a surface. they must scatter more light to space. If they darken the surface. they must be absorbing more. That cross over point is called the critical reflectance and in this paper we show that critical reflectance is a monotonic function of the intrinsic absorption properties of the particles. This parameter we call the single scattering albedo. We apply the technique to MODIS imagery over the Sahara and Sahel regions to retrieve the single scattering albedo in seven wavelengths, compare these retrievals to ground-based retrievals from AERONET instruments and compute error bars on each retrieval. The results show that we can retrieve single scattering albedo for pure dust to within +/-0.02 and mixtures of dust and smoke to within +/-0.03. No other space based instrument has achieved a retrieval of single scattering albedo that spans the spectrum from 0.47 microns to 2.13 microns and produces regional maps of aerosol absorption showing gradients and changes. Applied in a more operational fashion, such information will narrow uncertainties in estimating aerosol forcing on climate.

[1] In comparison to the lower atmosphere where comprehensive global atmospheric specifications are commonplace, the ability to perform routine global measurements of the properties of the atmosphere above the stratopause continues to be an active area of scientific research. In this paper, we revisit the use of infrasound as a remote sensing technique for horizontal winds in the upper atmosphere. To use infrasound to monitor the winds in the upper atmosphere, a sufficiently strong and persistent infrasound source is required. In addition, because of the highly attenuating nature of the thermosphere, the signals used must have low enough frequency content to survive. In this paper, impulsive signals from the Tungurahua volcano in Ecuador are used. This volcano has gone through periods of intense activity during which impulsive signals of dominant periods between 3 and 5 s are emitted. Depending on the atmospheric conditions, stratospheric, mesospheric, and thermospheric arrivals are observed. It is found that the traveltimes of the thermospheric arrivals exhibit a coherent variability with periods equal to those of the tidal harmonics. As such, these observations suggest a means of passive atmospheric remote sensing that can be utilized in conjunction with other techniques to routinely measure the state of the upper atmosphere.

Much like the better-known EI Nino-Southern Oscillation, the Madden-Julian Oscillation (MJO) is a global-scale atmospheric phenomenon. The MJO involves periodic, systematic changes in the distribution of clouds and precipitation over the western Pacific and Indian oceans, along with differences in wind intensity over even more extensive areas, including the north and subtropical Atlantic Ocean. The lead authors of this paper developed a sophisticated mathematical technique for mapping the spatial and temporal behavior of changes in the atmosphere produced by the MJO. In a previous paper, we applied this technique to search for modulation of airborne particle amount in the eastern hemisphere associated with the "wet" (cloudy) vs. "dry" phases of the MJO. The study used primarily AVHRR, MODIS, and TOMS satellite-retrieved aerosol amount, but concluded that other factors, such as cloud contamination of the satellite signals, probably dominated the observed variations. The current paper looks at MJO modulation of desert dust transport eastward across the Atlantic from northern Africa, a region much less subject to systematic cloud contamination than the eastern hemisphere areas studied previously. In this case, a distinct aerosol signal appears, showing that dust is transported westward much more effectively during the MJO phase that favors westward-flowing wind, and such transport is suppressed when the MJO reduces these winds. Aside form the significant achievement in identifying such an effect, the result implies that an important component of global dust transport can be predicted based on the phase of the MJO. As a consequence, the impact of airborne dust on storm development in the Atlantic, and on dust deposition downwind of the desert sources, can also be predicted and more accurately modeled.

[1] In the paper “Marine methane cycle simulations for the period of early global warming” by S. Elliott et al. (Journal of Geophysical Research, 116, G01010, doi:10.1029/ 2010JG001300, 2011), a mistake was made in the creation of Figure 7, which erroneously showed that only a small fraction (about 1%) of the inert methane tracer released from the ocean sediments into our model escaped to the atmosphere. The correct Figure 7 and its caption appear here. As can be seen in the corrected Figure 7, a much larger fraction is actually released to the atmosphere in this simulation (about 60%). It is important to note that the mistake was made in the analysis script, not in the simulations themselves, so all of the other figures are correct and the conclusions drawn from them are unchanged. [2] While this error has no effect on the majority of the paper, it does modify one significant point. We had originally concluded that, if only ∼1% of an inert methane tracer is transferred to the atmosphere, then the amount of a more realistic methane tracer that is consumed (possibly quite rapidly) would be much smaller, and likely insignificant. This conclusion may no longer be necessarily true, because our revised estimates indicate that several percentage points of the methane in the biologically active simulation escaped to the atmosphere, and the uncertainties in the biological losses are such that the amount escaping could be larger. Thus we conclude that release of shallow Arctic clathrate methane to the atmosphere may be more important than we had estimated in the original paper.

To develop the theory of FM CW radio acoustic sounding system (RASS), in this paper an analysis of influences from temperature gradient and radial range decay is presented. A nonconstant temperature gradient will significantly modify the spectrum of scattered signals and also cause a deviation of the maximum position of amplitude spectrum from the Bragg resonance, which should involve using any retrieval algorithm that will correct for this temperature bias. Without considering this effect, the error of 0.5–1 K will probably be introduced in the RASS temperature profile. An approximate retrieval algorithm is provided in text. Moreover, for the application of RASS using FM CW radar in lowest 100- to 200-m atmosphere, the far-field aspect sometimes will not be the case, and radial range decay will play a certain role, which is investigated also in this paper.

This paper looks at data from middle and high latitude ozonesonde stations in the northern hemisphere, to see how the ozone profile is changing over time. These changes are then cast in terms of other greenhouse gases, such a methane, carbon dioxide, chlorofluorocarbon refrigerants, and nitrous oxide. Ozone changes can manifest themselves in radiative effects in the atmosphere, as the ozone decreases can result in cooling due to a decrease in absorption and reemission of IR radiation from the surface. Such radiative effects can have an obvious impact on the climate, and this paper emphasized the climatic impact of such changes. While the stratospheric ozone levels have been falling, the tropospheric levels have been rising, and these effects must be considered together to assess climatic impacts.

This paper describes calculations of the spatial and temporal variation of the radiation budget of a tropical mesoscale convective system (MCS). A combination of cloud model simulations, radiation model simulations, and analyses of observations obtained during the Equatorial Mesoscale Experiment (EMEX), the Stratosphere-Troposphere Exchange Program (STEP), and the Australian Monsoon Experiment (AMEX) are used to obtain these heating rates. The two-dimensional version of the Colorado State University regional atmospheric modeling system is used to simulate a tropical MCS that occurred during EMEX mission 9 on February 2, 1987. The simulation is shown to broadly agree with the observations reported in a related paper. The spatial radiative heating distributions derived from a two-stream radiative transfer model corresponding to the mature stage of the simulated cloud system indicate that significant horizontal inhomogeneities exist. According to the model results the effects of the MCS are to (1) increase in the infrared emission to the surface and to decrease in the net infrared energy loss from the atmosphere relative to the clear sky emission and (2) change the transmission of solar flux to the surface, the shortwave albedo of the atmosphere, and the solar absorption in the atmosphere. The results show how the MCS significantly reduces the solar flux to the surface relative to the clear sky values and that the largest reduction occurs under the convective portions of the mature MCS. (3) The MCS creates a total (solar plus infrared) radiative warming in the atmosphere relative to the surrounding clear sky. The value of this total heating is governed by both infrared and solar absorption. Vertical profiles of this heating show the dominance of infrared cooling near cloud top and infrared heating inside and near cloud base. The shortwave heating rate can also be as large as the infrared cooling near the cloud top region of the tropical MCS, especially at a local noon. (4) The temporal changes in radiation profiles also demonstrate how the MCS modulates the radiation budget of the atmosphere. Specifically, the total radiation energy loss of the entire two-dimensional domain of the model atmosphere decreases and eventually becomes positive as the cloud system decays, becomes a stratiform in nature, and fills the domain. This change in the column divergence of flux translates into a total column radiative heating rate of approximately 1.7 K/d (relative to the clear sky radiative cooling rate). The solar component of this domain heating tends to be concentrated in the upper troposphere, whereas the infrared component of the heating is spread over the lower and middle troposphere. These results also show how tropical mesoscale cloud system provides an effective radiative heat source for the tropical atmosphere.

In paper 1 of this two-paper series (Simůnek and Suarez, this issue) we presented a description of the numerical model, SOILCO2, for CO2 transport and production in the unsaturated zone. In paper 2 the model sensitivity to various parameters is evaluated by both steady state and transient simulations, with a range in the parameter values typically found under field conditions. We also select parameter values for optimal plant and microbial CO2 production and production dependence on temperature, water content, osmotic potential and gas composition for plant and microbial respiration, all based on literature review. The predictive capabilities of the SOILCO2 model are evaluated by comparing model simulations to published field data from Missouri for three different crops and two growing seasons under transient conditions as well as a data set collected in Riverside, California, under relatively constant water content at depth. The model provided good prediction of the CO2 flux to the atmosphere as well as the concentrations in the root zone for all data sets.