Ground-level Observations Research Articles

Model analysis of seasonal variations in tropospheric ozone and carbon monoxide over East Asia

Temporal-spatial variations in tropospheric ozone concentrations over East Asia in the period from 1 January 2000 to 31 December 2004 were simulated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS). The simulated concentrations of ozone and carbon monoxide were compared with ground level observations at two remote sites, Ryori (39.03°N, 141.82°E) and Yonagunijima (24.47°N, 123.02°E). The comparison shows that the model reproduces their seasonal variation patterns reasonably well, and simulated ozone levels are generally in good agreement with the observed ones, but carbon monoxide concentrations are underestimated. Analysis of horizontal distributions of monthly averaged ozone mixing ratios in the surface layer indicates that ozone concentrations have noticeable differences among the four seasons; they are generally higher in the spring and summer while lower in the winter, reflecting the seasonal variation of solar intensity and photochemical activity and the fact that the monsoons over East Asia are playing an important role in ozone distributions.

A method for evaluating spatially-resolved NO<sub>x</sub> emissions using Kalman filter inversion, direct sensitivities, and space-based NO<sub>2</sub> observations

Abstract. An inverse modeling method was developed and tested for identifying possible biases in emission inventories using satellite observations. The relationships between emission inputs and modeled ambient concentrations were estimated using sensitivities calculated with the decoupled direct method in three dimensions (DDM-3D) implemented within the framework of the Community Multiscale Air Quality (CMAQ) regional model. As a case study to test the approach, the method was applied to regional ground-level NOx emissions in the southeastern United States as constrained by observations of NO2 column densities derived from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite instrument. A controlled "pseudodata" scenario with a known solution was used to establish that the methodology can achieve the correct solution, and the approach was then applied to a summer 2004 period where the satellite data are available. The results indicate that emissions biases differ in urban and rural areas of the southeast. The method suggested slight downward (less than 10%) adjustment to urban emissions, while rural region results were found to be highly sensitive to NOx processes in the upper troposphere. As such, the bias in the rural areas is likely not solely due to biases in the ground-level emissions. It was found that CMAQ was unable to predict the significant level of NO2 in the upper troposphere that was observed during the NASA Intercontinental Chemical Transport Experiment (INTEX) measurement campaign. The best correlation between satellite observations and modeled NO2 column densities, as well as comparison to ground-level observations of NO2, was obtained by performing the inverse while accounting for the significant presence of NO2 in the upper troposphere not captured by the regional model.

An adjoint sensitivity analysis and 4D-Var data assimilation study of Texas air quality

In this paper, we discuss the theory of adjoint sensitivity analysis and the method of 4D-Var data assimilation in the context of the Sulfur Transport Eulerian Model (STEM). The STEM atmospheric Chemical Transport Model (CTM) is used to perform adjoint sensitivity analysis and data assimilation over the State of Texas. We first demonstrate the use of adjoint sensitivity analysis for a receptor located at ground level in the Dallas Fort Worth (DFW) area. Simulations are carried out for three 36-h intervals in July 2004. One set of simulations focuses on a passive tracer, and illustrates the influence of meteorological conditions. The other results show the areas of influence associated with DFW ground level ozone, i.e. the areas where changes in precursors (O 3, NO 2, and HCHO) have the maximum impact on DFW ozone. Next, we employ data assimilation to optimize initial conditions of chemical fields and ground level emissions. We optimize the initial conditions for two episodes on 1 and 16 July 2004. Data assimilation makes use of AirNow ground level observations (for both episodes) and SCHIAMACHY NO 2 and HCHO observations from ENVISAT (for the 16 July episode). The re-analyzed chemical fields show considerable improved agreement with AirNow observations for non-initial conditions. We also perform inverse modeling of ground level emissions using data assimilation under an additional smoothness constraint. The results indicate higher NO 2 emission levels than in the current emission inventory in the DFW area, and lower emission levels in eastern Texas. The formaldehyde emissions are found to be larger than reported in a localized area near the Gulf Coast, and about at the reported level elsewhere. While the results obtained with the current state-of-the-art tools can help guide tuning of emission inventories, better constraints on the inverse problem are needed to obtain more rigorous quantitative estimates.

Performance characteristics of MM5–SMOKE–CMAQ for a summer photochemical episode in southeast England, United Kingdom

In this study a modelling system consisting of Mesoscale Model (MM5), Sparse Matrix Operator Kernel Emissions (SMOKE) and Community Multiscale Air Quality (CMAQ) model has been applied to a summer photochemical period in southeast England, UK. Ozone (O 3), nitrogen dioxide (NO 2) and particulate matter (PM 2.5) concentrations modelled with different horizontal grid resolutions (9 and 3 km) were evaluated against available ground-level observations from the UK Automatic Urban and Rural Network (AURN) and London Air Quality Network (LAQN) for the period of 24–28 June 2001 with a focus on O 3 predictions. This effort, which represents the first comprehensive performance evaluation of the modelling system over a UK domain, reveals that CMAQ's ability to reproduce surface O 3 observations varies with O 3 concentrations. It underpredicts O 3 mixing ratios on high-O 3 days and overpredicts the maximum and minimum hourly O 3 values for most low-O 3 days. Model sensitivity analysis with doubled anthropogenic NO x or volatile organic compounds (VOC) emissions and analysis of the daylight-averaged levels of OX (sum of O 3 and NO 2) as a function of NO x revealed that the undereprediction of peak O 3 concentrations on high-O 3 days is caused by the underprediction of regional contribution and to a lesser extent local production, which might be related to the underestimation of European emissions in EMEP inventory and the lacked reactivity of the modelled atmosphere. CMAQ systematically underpredicts hourly NO 2 mixing ratios but captures the temporal variations. The normalized mean bias for hourly NO 2, although much larger than that for O 3, falls well within the generally accepted range of −20% to −50%. CMAQ with both resolutions (9 and 3 km) significantly underpredicts PM 2.5 mass concentrations and fails to reproduce its temporal variations. While model performance for O 3 and PM 2.5 are not very sensitive to model grid resolutions, a better agreement between modelled and measured hourly NO 2 mixing ratios was achieved with higher resolution. Further investigation into the uncertainties in meteorological input, uncertainties in emissions, as well as representation of physical and chemical processes (e.g. chemical mechanism) in the model is needed to identify the causes for the discrepancies between observations and predictions.

Relativistic proton production at the Sun in the 20 January 2005 solar event

Based on the concept of multiple acceleration of solar energetic particles (SEP) we analyzed the super-event of 20 January 2005 by the data of ground level, balloon and spacecraft observations. The main characteristics of relativistic solar protons (energy spectra, anisotropy directions and pitch-angle distributions) are derived and their dynamics during the event is studied. It is shown that the flux of relativistic solar protons may consist of two distinct components, the so-called prompt and delayed ones. Within a two-source model of particle generation, one of which is associated with an expanding magnetic loop, we solved the transport equation in energy phase space, including adiabatic losses simultaneously with the stochastic acceleration process, and calculate the expected spectra of the delayed component at the source. The confrontation of experimental spectra with theoretical ones shows that the delayed component may be correctly described by stochastic acceleration, but not the prompt component. The required acceleration efficiencies turned out to be rather high, so that, for this particular event, adiabatic cooling is practically negligible. Our results provide a new support to the existence of two populations of relativistic solar protons in some SEP events.

A Simple Rainout Model for Radon Daughters

This paper presents a simplified time-independent model which calculates radioactivities of short-lived radon daughters in rainwater as a function of rainfall rate for unit concentration of radon in cloud. The model incorporates processes of impact collection for cloud droplets by raindrops, removal of raindrops from cloud and transport time of raindrops from the cloud base to the ground as forms of semi-empirical formulas. Radon concentrations in rain clouds are estimated from comparisons between model calculations and ground-level observations made over a few years.

A regional air quality model: Evaluation and simulation of O 3 and relevant gaseous species in East Asia during spring 2001

A regional air quality model (RAQM) has been introduced, evaluated and applied to investigate the behaviors of tropospheric O 3 and relevant species in East Asia. Model simulation is performed with an up-to-date monthly emission inventory [Streets, D.G., Bond, T.C., Carmichael, G.R., Fernandes, S.D., Fu, Q., He, D., Klimont, Z., Nelson, S.M., Tsai, N.Y., Wang, M.Q., Woo, J.-H. and Yarber, K.F., 2003. An inventory of gaseous and primary emissions in Asia in the year 2000. Journal of Geophysical Research 108 (D21), 8809. doi:10.1029/2002JD003093] for March 2001 when extensive experimental data sets were available, including ground-level observations and the TRACE-P (TRAnsport and Chemical Evolution over the Pacific) aircraft experiments, which allow a comprehensive evaluation for this model system. Model validation demonstrates that RAQM is able to represent most of the major processes of chemical species in the troposphere, with model results agreeing with observations reasonably well. Statistical analysis has been conducted for both meteorological parameters (wind speed, temperature and humidity) and chemical components (10 key gaseous species) by comparing with the TRACE-P data sets. At altitudes <5 km, the correlations ( R) for meteorological parameters are all above 0.8, with temperature the highest (0.97). The model produces the highest R for O 3 (around 0.75), followed by CO (0.66–0.72) and HO 2 (0.7), and the lowest R for NO x (0.1–0.2), with R = 0.4–0.7 for the remaining species. The model successfully reproduces the major features in chemical transport associated with the Asian outflow and reasonably explains the observed fluctuation in species concentrations at downwind monitoring sites over the western Pacific.

Simulation of tropospheric ozone with MOZART-2: An evaluation study over East Asia

Climate changes induced by human activities have attracted a great amount of attention. With this, a coupling system of an atmospheric chemistry model and a climate model is greatly needed in China for better understanding the interaction between atmospheric chemical components and the climate. As the first step to realize this coupling goal, the three-dimensional global atmospheric chemistry transport model MOZART-2 (the global Model of Ozone and Related Chemical Tracers, version 2) coupled with CAM2 (the Community Atmosphere Model, version 2) is set up and the model results are compared against observations obtained in East Asia in order to evaluate the model performance. Comparison of simulated ozone mixing ratios with ground level observations at Minamitorishima and Ryori and with ozonesonde data at Naha and Tateno in Japan shows that the observed ozone concentrations can be reproduced reasonably well at Minamitorishima but they tend to be slightly overestimated in winter and autumn while underestimated a little in summer at Ryori. The model also captures the general features of surface CO seasonal variations quite well, while it underestimates CO levels at both Minamitorishima and Ryori. The underestimation is primarily associated with the emission inventory adopted in this study. Compared with the ozonesonde data, the simulated vertical gradient and magnitude of ozone can be reasonably well simulated with a little overestimation in winter, especially in the upper troposphere. The model also generally captures the seasonal, latitudinal and altitudinal variations in ozone concentration. Analysis indicates that the underestimation of tropopause height in February contributes to the overestimation of winter ozone in the upper and middle troposphere at Tateno.

CLINICAL TRIALS LITIGATION: PRACTICAL REALITIES AS SEEN FROM THE TRENCHES

Litigation involving human clinical research trials has escalated rapidly in the past few years. Whereas these suits raise many important theoretical questions, they also have important practical and human dimensions of which many people are unlikely to be aware until, by some unfortunate turn, they must live the reality. From the vantage of a fairly close view on one recent lawsuit, this article offers some ground-level observations and reflections that, it is hoped, may be of use to people in clinical research who might one day find themselves in a similar position.

A study of the ground level enhancement of 23 February 1956

One of the greatest and most famous increase of solar cosmic rays over the neutron monitor epoch is the ground level enhancement in 1956. All future proton events are inevitable when compared with this one and therefore it is necessary to provide the efficiency of such a comparison derived from the existing data. In this paper, we return to the analysis of ground level observations on 23 February 1956 in order to model more precisely the solar cosmic ray behaviour. The extremely high magnitude of this effect allowed various spectral characteristics of solar cosmic rays, their anisotropy, differential and integral proton fluxes, and angular distribution of the source of solar particle anisotropy to be obtained with sufficient accuracy on the basis of available data from 13 neutron monitors. The most outstanding feature of this event was a narrow and extremely intensive beam of ultra relativistic particles arriving at Earth at the beginning of the event. This unique beam was not long and its width did not exceed 30–40°, thus, its contribution to solar particle density was not significant. Many features of this GLE are apparently explained by the peculiarity of particle interplanetary propagation from a remote (limb or behind of limb) source.

Modeling of organic carbon aerosol distributions over east asia in the springtime

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to investigate the transport and evolution processes of organic carbon (OC) aerosols in the springtime of 2001. The simulated OC mixing ratios are compared with ground level observations at three remote sites in Japan during the Aerosol Characterization Experiment ? Asia (ACE-Asia) field campaign. It is found that the modeled OC concentrations are generally in good agreement with the observed ones, and the model reproduces the time variations in OC mixing ratios reasonably well. Model results show that high levels (larger than 16 mg·m −2) of column burden of OC aerosols concentrated in the middle reaches of Yangtse River and southern China, and that in most regions of China to the south of Yellow River the column burden was over 7 mg·m −2, while the isopleth of 4 mg·m −2 extended to the inner area of northwestern Pacific Ocean.

A numerical study of tropospheric ozone in the springtime in East Asia

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to study the transport and photochemical transformation of tropospheric ozone in March 1998. The calculated mixing ratios of ozone and carbon monoxide are compared with ground level observations at three remote sites in Japan and it is found that the model reproduces the observed features very well. Examination of several high episodes of ozone and carbon monoxide indicates that these elevated levels are found in association with continental outflow, demonstrating the critical role of the rapid transport of carbon monoxide and other ozone precursors from the continental boundary layer. In comparison with available ozonesonde data, it is found that the model-calculated ozone concentrations are generally in good agreement with the measurements, and the stratospheric contribution to surface ozone mixing ratios is quite limited.

Prediction of the Vertical Profile of Ozone Based on Ground-Level Ozone Observations and Cloud Cover

A number of statistical techniques have been used to develop models to predict high-elevation ozone (O3) concentrations for each discrete hour of day as a function of elevation based on ground-level O3 observations. The analyses evaluated the effect of exclusion/inclusion of cloud cover as a variable. It was found that a simple model, using the current maximum ground-level O3 concentration and no effect of cloud cover provided a reasonable prediction of the vertical profile of O3, based on data analyzed from O3 sites located in North Carolina and Tennessee. The simple model provided an approach that estimates the concentration of O3 as a function of elevation (up to 1800 m) based on the statistical results with a ±13.5 ppb prediction error, an R2 of 0.56, and an index of agreement, d 1, of 0.66. The inclusion of cloud cover resulted in a slight improvement in the model over the simple regression model. The developed models, which consist of two matrices of 24 equations (one for each hour of day for clear to partly cloudy conditions and one for cloudy conditions), can be used to estimate the vertical O3 profile based on the inputs of the current day’s 1-hr maximum ground-level O3 concentration and the level of cloud cover.

Formation of a Polarization Jet during the Expansion Phase of a Substorm: Results of Ground-Based Measurements

The ground-based polarization jet measurements at the Yakutsk ionosphere station (L= 3.0) for the years 1989–1991 (110 events) are compared with variations of the AE-index and with parameters of the local magnetic activity. It is shown that polarization jet development in the near midnight sector can occur during a period of no longer than 10 min on the expansion phase of a substorm. The formation of the polarization jet is accompanied by a specific magnetic field variation corresponding in shape to a fast passage of the Harang Discontinuity above the station. Statistical data are given on ground level observations of the polarization jet, which are close to those measured from satellites. The mean delay (averaged over the full data bank) between the onset of a substorm with AE≥ 500 nT and the moment of the polarization jet appearance at L= 3.0 is equal to 0.5 h near midnight and to 1.0 – 1.5 h in the evening sector. Estimations show that the duration of the polarization jet formation when energetic ions are injected into the Harang Discontinuity region above the ground station can last for about 10 min, and during this time the Harang Discontinuity can be shifted to the west. This is in qualitative agreement with the described observations.

Large Scale Modulation: View from the Earth

The current knowledge and ideas, obtained from groundlevel observations and concerning the solar modulation of cosmic rays, are reviewed. The following topics are discussed: observations of the cosmic ray modulation at the Earth and main characteristics of the accumulated experimental data; manifestations of the solar magnetic cycle in cosmic rays; the effect of hysteresis and its relation to the size of the heliosphere; the rigidity spectrum of long-term cosmic ray variations; the influence of the sporadic effects on long-term modulation; long-term variations of cosmic ray anisotropy and gradients; the place of groundlevel observations in current studies of cosmic ray modulation and their future prospects. Particular consideration is given to the correlation of long-term cosmic ray variations with different solar-heliospheric parameters, and to empirical models of cosmic ray modulation.

ANALYZING THE SOLAR PROTON EVENT OF 22 OCTOBER 1989, USING THE METHOD OF SPECTROGRAPHIC GLOBAL SURVEY

Using ground-level observations of cosmic-ray (CR) intensities from a worldwide network of stations during the ground-level enhancement (GLE) of 22–23 October 1989, variations of the particle distribution function in all phases of the event were investigated.

The polarization of auroral radio emissions

Ground level observations using two vertical loop antennas oriented at 90° to each other reveal the sense of polarization of several types of auroral radio emissions in the frequency range 30–5000 kHz. Auroral hiss is observed to be right elliptically polarized (RP) with respect to the local magnetic field, consistent with theoretical expectation for the whistler mode and with earlier measurements. Two less well‐understood auroral emissions, are found to be left elliptically polarized (LP). This polarization is inconsistent with their generation in the X‐mode as suggested by some theories.

Seeing Tests at Four Sites in Support of the NPOI Project

view Abstract Citations (5) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Seeing Tests at Four Sites in Support of the NPOI Project Hutter, D. J. ; Elias, N. M., II ; Peterson, E. R. ; Weaver, W. B. ; Weaver, G. ; Mozurkewich, D. ; Vrba, F. J. ; Simon, R. S. ; Buscher, D. F. ; Hummel, C. A. Abstract This paper reports astronomical seeing measurements made at four sites in the western United States during 1991-92. This study was conducted as part of the site selection process for the Navy Prototype Optical Interferometer. An extensive series of observations were made at Chews Ridge and Anderson Ridge, CA (≍36 000 equivalent FWHM seeing estimates). Observations made from Chews Ridge over 49 nights yield an average FWHM seeing value of 1."1, while those made from Anderson Ridge over 34 nights yield an average FWHM seeing of ≍1:4. However, observations made from Anderson Ridge at a location away from any nearby trees indicate that more open sites in that area may enjoy seeing comparable to that measured at Chews Ridge. Simultaneous free-air, ground-level observations at the U.S. Naval Observatory's Flagstaff Station and at Anderson Mesa, both near Flagstaff, AZ, yield similar seeing values to each other (≥0".1 difference). Publication: The Astronomical Journal Pub Date: December 1997 DOI: 10.1086/118690 Bibcode: 1997AJ....114.2822H Keywords: SITE TESTING full text sources ADS | data products CDS (1)

Sulfur hexafluoride—A powerful new atmospheric tracer

Long-term observations of the atmospheric trace gas sulfur hexafluoride (SF 6) at four background monitoring stations, Neumayer, Antarctica (1986–1994), Cape Grim, Tasmania (1978–1994), Izafña, Canary Islands (1991–1994) and Alert, Canada (1993–1994) are presented. These data sets are supplemented by two meridional profiles collected over the Atlantic Ocean (1990 and 1993) and occasional observations at the regional site Fraserdale, Canada (1994). The analytical system and the method of SF 6 calibration are described. Compared with data from Neumayer and Izafia reported earlier, measurements are updated for all sites until the end of 1994 and the precision has improved by more than a factor of 2. With the Cape Grim archived air samples, the atmospheric SF 6 chronology is extended by 8 more years back to 1978. For the period from January 1978 to December 1994 the data confirm a stable and unbroken quadratic rise in tropospheric SF 6 from 0.50 to 3.11 ppt in the southern hemisphere and for July 1991 to December 1994 from 2.69 to 3.44 ppt in the northern hemisphere. The global mean tropospheric increase rate in late 1994 was 0.225 ppt yr −1 (6.9% yr −1). The long term trend and interhemispheric gradients are due to industrial production and emission, rising approximately linearly with time and located predominantly (94%) in the northern hemisphere. The interhemispheric exchange time (1.7 ± 0.2 yr) derived from SF 6 ground level observations when using a two-box model of the atmosphere is considerably larger if compared to the exchange time derived from two- and three-dimensional models (1.1 yr). The chemical and biological inertness of SF 6 up to stratospheric conditions results in an atmospheric lifetime of more than 800 years and makes SF 6 a powerful tool for modelling transport processes in the atmosphere. Moreover, the tropospheric SF 6 chronology is a very valuable input function for mixing studies in linked compartments like the stratosphere, the hydrosphere and the cryosphere.

A Photoelectric Detector Suspended under a Balloon for Actinic Flux Measurements

An instrument to measure ultraviolet actinic flux in and outside clouds was constructed and calibrated. Characteristics of the instrument axe: 1) it is equipped with gallium phosphide photodiodes, 2) its isotropic directional response is almost perfect due to the special design of the optical diffusers, and 3) it is a lightweight construction (150 g) allowing the use of a balloon or a kit as an observation platform. Ground-level observations and vertical profiles, measured with this UV photometer in clear air and in stratocumulus during the Atlantic Stratocumulus Transition Experiment in the Azores, confirm that the Madronich radiation transfer model is valid for clouds.