Reference Atmosphere Research Articles

The experiment study to assess the impact of hydrogen blended natural gas on the tensile properties and damage mechanism of X80 pipeline steel

Environmental hydrogen embrittlement has become a non-negligible problem in the hydrogen blended natural gas transportation. To qualitatively study the degradation mechanism of X80 steel used in the natural gas pipelines, the slow strain tensile experiments are carried out in this work. The nitrogen and hydrogen are adopted to simulate the hydrogen blended natural gas to explore the tensile properties of X80 steel. According to the volume proportion of hydrogen, the test atmospheres are divided into the reference atmosphere and the hydrogen-contained atmospheres of 1%, 2.2% and 5%. The tensile experiments of the smooth and notched specimens are conducted in the above gas atmospheres. Mechanical properties and fracture morphologies after stretching are further analyzed. The results show that the hydrogen blended natural gas has little effect on the tensile and yield strengths. Distinguished from the hydrogen volume proportion of 1% and 2.2%, with the increase of hydrogen proportion, the effect of hydrogen on mechanical properties of specimens increases significantly. Moreover, the deteriorated mechanical properties of notched specimens are more seriously than those of smooth specimens. This work provides the basis for safe hydrogen proportion for X80 pipeline steel when transporting hydrogen blended natural gas.

Practical Considerations with Radar Data Height and Great Circle Distance Determination

AbstractOwing to their ease of use, “simplified” propagation models, like the Equivalent Earth model, are commonly employed to determine radar data locations. With the assumption that electromagnetic rays follow paths of constant curvature, which is a fundamental assumption in the Equivalent Earth model, propagation equations that do not depend upon the spatial transformation that is utilized in the Equivalent Earth model are derived. This set of equations provides the true constant curvature solution and is less complicated, conceptually, as it does not depend upon a spatial transformation. Moreover, with the assumption of constant curvature, the relations derived herein arise naturally from ray tracing relations.Tests show that this new set of equations is more accurate than the Equivalent Earth equations for a “typical” propagation environment in which the index of refraction n decreases linearly at the rate dn/dh = -1/4a, where h is height above ground and a is the Earth’s radius. Moreover, this new set of equations performs better than the Equivalent Earth equations for an exponential reference atmosphere, which provides a very accurate representation of the average atmospheric n structure in the United States. However, with this n profile the equations derived herein, the Equivalent Earth equations, and the relation associated with a flat Earth constant curvature model produce relatively large height errors at low elevations and large ranges.Taylor series approximations of the new equations are examined. While a second-order Taylor series approximation for height performs well under “typical” propagation conditions, a convenient Taylor series approximation for great circle distance was not obtained.

DART: Improvement of thermal infrared radiative transfer modelling for simulating top of atmosphere radiance

Land surface temperature (LST) is increasingly needed for studying the functioning of the Earth's surface at local to global scale. Radiative transfer (RT) models that simulate top of atmosphere (TOA) radiance are essential tools to derive accurate LST from thermal infrared (TIR) signals of Earth observation (EO) satellites. DART (Discrete Anisotropic Radiative Transfer) is one of the most accurate and comprehensive three-dimensional models that simulate RT in the Earth-atmosphere system. Up to version 5.7.3, the mean absolute error (MAE) of DART atmospheric TIR radiance of six standard atmospheres (USSTD76, TROPICAL, MIDDLATSUM, MIDDLATWIN, SUBARCSUM, SUBARCWIN) over 3.5 μm - 20 μm was 3.1 K compared to the reference atmospheric RT model MODTRAN, which is much larger than the 1 K accuracy needed by most LST applications. Also, the radiance error reached 2.6 K for some TIR bands whereas the noise equivalent differential temperature (NeDT) of satellite TIR sensor is usually less than 0.4 K. Recently, the DART atmospheric RT modelling was greatly improved by (1) introducing the equivalent absorption cross-section of five most absorbing gases (H2O, CO2, O3, CH4, N2O), and (2) implementing a double-layer thermal emission method. The MAE of DART atmospheric TIR radiance of six standard atmospheres and actual atmospheres over France and the Mediterranean Sea is now better than 1.0 K. The band radiance error is less than 0.2 K in the EO satellite TIR bands. DART is still accurate if the temperature profiles of standard atmospheres are offset by less than 6 K and if the viewing zenith angle is less than 50°. In short, the improved DART meets the requirements of both LST applications, and present and future TIR EO satellite missions. It is already available to scientists (https://dart.omp.eu).

Neutral Exospheric Temperatures From the GOLD Mission

AbstractObservations of far‐ultraviolet (FUV) dayglow by the Global‐scale Observations of Limb and Disk (GOLD) mission provide a new opportunity for determining how geomagnetic storms alter the temperature of the thermosphere and enable us to quantify the global‐scale response of the thermosphere to solar extreme‐ultraviolet (EUV) variability. Relative temperature changes can be measured by monitoring changes in the scale height of molecular nitrogen as observed in Lyman‐Birge‐Hopfield (LBH) band emissions. Mean scale heights are derived from GOLD FUV observations using Chapman function fits to altitude profiles of LBH band emissions. We provide an overview of the theoretical basis for the GOLD Level 2 exospheric temperature algorithm, including a generalization of a standard Chapman function fitting technique to allow for gravity and temperature gradients. Effects on derived exospheric temperatures from instrument artifacts and stars in the GOLD field of view are reviewed. We also discuss GOLD Level 1C LIM and Level 2 TLIMB data products and present representative examples of each. We show that exospheric temperatures vary with local time and correlate weakly with solar activity but more strongly with geomagnetic activity. Finally, we present results from a preliminary data product validation that show good qualitative agreement with predictions from a global reference atmospheric model.

The Refraction Correction of Elevation Angle for the Mean Annual Global Reference Atmosphere

In some frequency-sharing studies between fixed service and space radiocommunication services, including fixed-satellite, broadcasting-satellite, and space science services, it is necessary to estimate the apparent elevation angle of a space station, taking into account the atmospheric refraction. Recommendations ITU-R (International Telecommunication Union—Radiocommunication) P.834-9 and F.1333-1 detail similar methods regarding calculating the refraction correction for the elevation angle of the mean annual global reference atmosphere. Herein, both methods are approximated using the bending angle from the ground to the infinity height; this approach is most suitable for geosynchronous orbit satellites. In this paper, new methods for calculating the refraction correction for the elevation angle are proposed regarding the mean annual global reference atmosphere given in Recommendation ITU-R P.835-6. Specifically, the results of the ray-tracing method are fitted. The height of the new formulae is 100 km above sea level. For higher altitudes, correction methods are given based on free-space propagation. The proposed methods can be applied to the calculation of the refraction correction for the elevation of the mean annual global reference atmosphere for satellites at different orbital heights. Furthermore, these new methods compare favourably to the two ITU-R Recommendations.

A Review on GRAPES-TMM Operational Model System at Guangzhou Regional Meteorological Center

This review summarizes the general developments of the operational mesoscale model system based on the Global/Regional Assimilation and Prediction System-Tropical Monsoon Model (GRAPES-TMM) at the Guangzhou Regional Meteorological Center. GRAPES-TMM consists of the Tropical Regional Atmospheric Model System for the South China Sea (TRAMS, a typhoon model with a horizontal resolution of 9 km), the Mesoscale Atmospheric Regional Model System (MARS, 3km) and the fine-scale Rapid Update Cycling (RUC, 1km) forecasting system. The main advances of model dynamical core and physical processes are summarized, including the development of the 3D reference atmosphere scheme, the coupling scheme between dynamics and model physics, the calculation of nonlinear terms by fractional steps, the gravity wave drag scheme induced by sub-grid orography and a simplified model for landsurface scheme. The progress of model applications is reviewed and evaluated. The results show that the updated 9-3-1 forecasting system provides an overall improved performance on the weather forecasting in south China, especially for typhoon-genesis and typhoon-track forecasting as well as short-range weather forecasting. Capabilities and limitations as well as the future development of the forecasting system are also discussed.

Effects of Moisture in a Two-Layer Model of the Midlatitude Jet Stream

AbstractThe effects of moisture on the energetics of a statistically stationary, baroclinically unstable jet representing the midlatitude atmosphere are examined using a two-layer, β-plane shallow-water model. Flow is driven by a relaxation of the interface between the two layers to a baroclinically unstable profile. Moisture is input to the lower layer by evaporation. When supersaturation occurs, precipitation is triggered and the related latent heat release drives a mass transfer between the two layers. A comparison between dry and moist reference atmospheres shows that precipitation reduces eddy kinetic energy. This is related to the meridional distribution of precipitation, which occurs on the poleward side of the jet (where the interface field is raised). This latitudinal structure of precipitation is related to a correlation between poleward flow and ascent, which is analyzed using a shallow-water analog to the ω equation. The precipitation effect on the energy budget is predominately due to zonal- and time-averaged terms. Because of this, dry simulations in which the thermal forcing is modified to mimic the effect of zonally averaged precipitation are carried out and compared with their precipitating counterparts. These simulations show a similar reduction of baroclinic eddy kinetic energy; however, the barotropic eddy kinetic energy response shows a larger difference.

Disturbed motion of the hypersonic first stage of an aerospace system in climb

Disturbed motion of the hypersonic first stage of an aerospace system in climb is analyzed. Deviations of atmospheric density from standard values and deviations of aerodynamic force coefficients from reference values are taken as disturbances. Disturbance motion of the hypersonic first stage of a hypersonic vehicle with the optimal angle-of-attack schedule obtained for reference atmosphere and nominal aerodynamic characteristics is modeled. Deviations of terminal conditions of disturbed motion from the target values of velocity, altitude and flight path inclination are determined. The problem of minimum propellant mass consumed in the climb with acceleration to hypersonic velocity is solved for disturbed motion by the method of Pontryagins maximum principle. Optimal angle-of-attack schedules, optimal flight paths and finite values of the mass of the hypersonic first stage are determined. Comparative analysis of optimal control programs and flight paths for disturbed and undisturbed motion is made.

Experimental facility for the production of reference atmosphere of radioactive gases (Rn, Xe, Kr, and H isotopes)

Radioactive gases are of great interest for environmental measurements and can be distinguished in two categories. The natural radionuclides such as the isotopes of radon (222Rn and 220Rn), and the anthropogenic radionuclides coming from fission products (isotopes of Xe and 85Kr) and activation products (3H and 37Ar). Gas monitoring in the environment is an important issue for radioprotection and for the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which both require metrological traceability of these gases. For this purpose, two gas chambers, of 42 L and 125 L, have been conceived and built at the LNE-LNHB to produce reference atmospheres of various gas mixtures. These chambers were created in order to provide any radioactive gas atmosphere with a wide range of activity concentrations (Bq·m−3 to MBq·m−3). The goal of this setup is to be representative of the different environmental conditions for detector qualification and to perform studies of radioactive gas absorption in materials of interest. As a result, the 2 chambers used in this experimental facility are designed to work from vacuum pressure to atmospheric pressure, with a constant activity concentration for any radioactive gas, and under dry to high humidity conditions. It can also be used in a static mode, in which the activity concentration will follow the radioactive decay of the gas. In this paper, the characterization of the chambers will be discussed. These two chambers are combined with different primary standards established by the LNE-LNHB. As the production of the reference atmosphere depends on the primary standard method, we present the details for each atmosphere production, which require a well-known volume, pressure or a direct activity concentration measurement.

A new primary emanation standard for Radon-222

New emanation sources for Rn-222 have been developed by electrodeposition of Ra-226 onto stainless-steel discs. With a high resolution of up to 20 keV FWHM in the Ra-226 peak at 4.87 MeV, defined solid-angle alpha-particle spectrometry is the method of choice to determine the deposited Ra-226 activity. The amount of emanating Rn-222 is determined by gamma-ray spectrometry using HPGe-detectors. The measurement is based on the distorted equilibrium of the Ra-226 decay chain due to Rn-222 emanation. Comparative gamma-ray spectrometric measurements with sealed, Rn-222 tight sources of the same type and geometry make the knowledge of emission probabilities and detection efficiency unnecessary. The new emanation sources allow the production of stable reference atmospheres in the regime below 300 Bq⋅m−3 with uncertainties not exceeding 2% for k = 1.

(Invited) Zirconia-Based Electrochemical Oxygen Sensor for Monitoring Humidity at the Cathode of PEM Stacks

One of the greatest challenges associated with PEMFCs is the water balance in thefuel cell stack. Depending upon the load and the operating conditions, the fuel cell membranes have a propensity to both flood and dry-out. If the PEM is not adequately humidified, the conductivity of the protons decreases, which causes reduced performance. Excess water also can create an issue by inhibiting the reactants from diffusing to the catalyst sites by flooding of the electrodes and gas channels if the water removal is insufficient. Current humidity sensing technologies are not capable of meeting the demands required for this harsh environment. Zirconia-based electrochemical sensors for measuring the oxygen concentration in the automotive exhaust have been used on vehicles for nearly 40 years. This oxygen sensor is an electrochemical cell based on oxygen-ion conducting zirconia operated at elevated temperatures (> 400°C). The sensor is a simple Nernst cell that consists of a single electrochemical cell with one electrode exposed to a reference atmosphere (typically air) and the other electrode exposed to the measurement (exhaust) gas. Although successfully used for stoichiometric A/F control for many years, Nernst-type oxygen sensors are not useful for applications away from stoichiometry because of their weak logarithmic dependence of the emf on oxygen partial pressure. Single and double-zirconia-cell sensors have been developed which have much higher sensitivity and thus a wider range of operation. These are amperometric sensors are based on oxygen pumping, which involves the transfer of oxygen from one side of a zirconia cell to the other by passing an electric current through the device. Since these sensors operate over a wide range, they are referred to as “wide-range oxygen” or “universal exhaust gas oxygen” (UEGO) sensors and can be used over a broader range of A/F measurement and control. All gasoline vehicles, as well as diesel powertrains which operate lean, employ UEGO sensors to meet the emission requirements. The double-cell amperometric sensor also can be used to measu­re the concentration of other oxygen-containing molecules, e.g. H2O, CO2, SO2, and NOx. In order to mea­sure the H2O concentration for example, a voltage is applied across the pump-cell that is greater than the dissociation potential for H2O. The resulting oxygen generated from the decomposition of water is then measured via an increase in pumping current by the UEGO sensor and is proportional to the H2O concentration in the gas. If other oxygen-containing molecules are present in the measurement gas, the voltage across the pump cell can be varied over the dissociation potentials of these gases. For H2O/air mixtures, the concentration of oxygen can be measured at a lower potential. A second voltage larger than the dissociation potential of the measurement gas, H2O, is applied to measure the concentration of oxygen plus water. The water concentration can be determined by subtracting the pumping current due to oxygen from the pumping current due to the combination of the two gases. Other gases can also be measured in a similar fashion. These measurements can be achieved without any modification to the existing sensor hardware. A simple modification to the electronic control circuitry is all that is required to perform this type of measurement. Figure 1 shows the sensitivity of a commercially available UEGO sensor for the dissociation of H2O as a function of dissociation potential. A typical operating value for the sensing voltage Vs for oxygen measurement is 450 mV. The plot below was generated from data measured in the lab at various water concentrations in a carrier gas of dry nitrogen. From the plot it is evident that water dissociation is occurring at potentials less than 800 mV. Additionally, the output begin to saturate at a potential approaching 1100 mV, suggesting that full dissociation of the water has been achieved. Figure 2 shows the sensitivity (pumping current) of the same sensor as a function of water concentration for Vs = 1080 mV. Once again the carrier gas is dry nitrogen. The output is linear in water concentration. The water balance at the cathode is particularly difficult to manage because water accumulates due to the reaction and the clogging of the small channels. Controlling this water balance requires accurate water concentration measurements at temperatures approaching 100°C and pressures up to 3 bar absolute. The application of this humidity sensing technology to measure the water concentration at the cathode of PEMFCs will be discussed. Figure 1

Effects of perturbing a reference atmosphere on sonic boom propagation and metrics

There is substantial interest in the accurate noise prediction that ranges from sonic boom noise from conventional supersonic aircraft to low-boom noise (a sonic thump sound) from future aircraft designed for quiet flight. A carefully designed reference atmosphere was developed for comparing multiple sonic boom propagation programs. In the current work, that reference atmosphere was perturbed in a number of ways to assess the importance of each perturbation. The code PCBoom was used for this study, and the perturbations were for the temperature, humidity, and wind profiles. One result is that in the absence of winds, perturbing the temperature profile does not substantially affect the metrics on the ground, but perturbing the humidity profile does. [Work supported by the U.S. Federal Aviation Administration Office of Environment and Energy through ASCENT, the FAA Center of Excellence for Alternative Jet Fuels and the Environment, Project 41 through FAA Award No. 13-C-AJFE-PSU under the supervision of Sandy Liu. Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the FAA.]

On the relative roles of the neutral density and photo chemistry on the solar zenith angle variations in the V2 layer characteristics of the Venus ionosphere under different solar activity conditions

Using an in-house developed one dimensional photo-chemical model (1D-PCM), which considers production and loss of 11 ions namely, CO2+, CO+, C+, N2+, N+, He+, O+(2D), O+(2P), O+(4S), O2+ and NO+, characteristics of the V2 layer in the Venus ionosphere has been studied. It is noted that existing ionospheric model for the Venus ionosphere, such as the IonA (Ionization in Atmospheres) model, not only over/under estimate the peak electron density of V2 layer, it also has significant departures from the observations on the solar zenith angle and solar activity control. The IonA model uses VenusGRAM model (Venus Global Reference Atmosphere Model) as input for the neutral density and temperature and considers Venus atmosphere consisting of CO2, O, and N2 molecules only. Further, it oversimplifies the ion chemistry by assuming Venus ionosphere to have O2+ as the only dominant ion species. Using VTS3 model, an empirical model based on measurements from Orbiter Neutral Mass Spectrometer on Pioneer Venus Orbiter (PVO) which considers profiles of six neutrals (CO2, O, CO, He, N, and N2), we modified IonA model, named as IonA-VTS3, to find that it reproduced the altitude of V2 peak electron density (hmV2) quite well. However, the model still lacked in reproducing observed peak V2 electron density (NmV2). The in-house developed one dimensional photo-chemical model (1D-PCM) not only estimated NmV2 accurately, the hmV2 was also reproduced quite well. Comparison of Venera and PVO radio occultation measurements with 1D-PCM and IonA-VTS3 calculations reveals the role of complex chemical reactions in determining the features of peak altitude and density of V2 layer during different solar activity periods. We surmised that differences in the observed and IonA modeled peak V2 layer altitudes were due to the limitations associated with VenusGRAM neutral density model. It shows that variations in the neutral density controls the V2 layer peak density height. 1D-PCM calculations also showed that the complex chemistry including production and loss reactions of 11 ions could reproduce the variations in the peak density of Venusian ionosphere during different solar activity conditions. It suggests that the ion-chemistry has wider control over the peak plasma density in the Venus ionosphere.

Zirconia-Based Electrochemical Oxygen Sensor for Accurately Determining Water Vapor Concentration

Zirconia-based electrochemical sensors for measuring the oxygen concentration in the automotive exhaust have been used on vehicles for nearly 40 years. The oxygen sensor is an electrochemical cell based on oxygen-ion conducting zirconia. The sensor consists of a single electrochemical cell which has one electrode exposed to a reference atmosphere (typically air) and the other electrode exposed to the measurement (exhaust) gas and operates as a simple Nernst cell. The open circuit voltage of this zirconia electrochemical cell changes with variations in the oxygen partial pressures existing adjacent to its two electrodes. The emf generated by this Nernst cell gives a measurement of the concentration of oxygen in the exhaust gas. This measurement can be used by the engine control unit to adjust the air-to-fuel ratio so as to maintain it close to stoichiometry, thereby minimizing the unwanted emissions. All gasoline (and some diesel) vehicles produced today utilize an oxygen sensor to control their emission systems. Although successfully used for stoichiometric A/F control for many years, Nernst-type oxygen sensors are not useful for applications away from stoichiometry because of their low sensitivity (i.e. weak logarithmic dependence of the emf on oxygen partial pressure). However, double-zirconia-cell sensors have been developed [1,2] which have much higher sensitivity and thus a wider range of operation and are therefore applicable to A/F measurement and control from very rich to very lean A/F mixtures. These sensors are based on oxygen pumping, which involves the transfer of oxygen from one side of a zirconia cell to the other by passing an electric current through the device. Since these sensors operate over a wide range, they are referred to as “wide-range oxygen” or “universal exhaust gas oxygen” (UEGO) sensors. Most gasoline vehicles, as well as diesel powertrains which operate lean, employ UEGO sensors to meet the emission requirements. A double-cell oxygen-pumping device (UEGO sensor) also can be used to measu­re the concentration of other oxygen-containing molecules in the exhaust gas, e.g. H2O, CO2, SO2, and NOx. In order to mea­sure the H2O concentration, a voltage is applied across the pump-cell that is greater than the dissociation potential for H2O. A measurement of the pumping current through the cell provides a measure of the oxygen generated from the decomposition of water and thus a measure of the H2O concentration in the gas. However, in the exhaust gas this measurement is confounded by the fact that molecular oxygen and other molecules also are dissociated. If the concentrations of these other molecules were constant, then the concentration of H2O could still be determined uniquely by subtracting the contribution of these other molecules. However, the concentrations of the different oxygen-containing molecules in the exhaust gas vary with engine operating conditions. This problem can be overcome by varying the voltage across the pump cell and measuring the pumping currents at various dissociation potentials. At a lower potential the concentration of oxygen can be measured. A second voltage larger than the dissociation potential of the measurement gas, H2O e.g., is applied to measure the concentration of oxygen plus water. The water concentration can be determined by subtracting the pumping current due to oxygen from the pumping current due to the combination. Other gases, CO2 e.g., can also be measured in a similar fashion. In principle, these measurements can be achieved without any modification to the existing sensor hardware. A simple modification to the electronic control circuitry is all that is required to perform this type of measurement. Figure 1 shows the sensitivity of a commercially available UEGO sensor for the dissociation of H2O as a function of dissociation potential. A typical operating value for the sensing voltage Vs for oxygen measurement is 450 mV. The plot below was generated from data measured in the lab at various water concentrations in a carrier gas of dry nitrogen. From the plot it is evident that water dissociation is occurring at potentials less than 800 mV. Additionally, the output begin to saturate at a potential approaching 1100 mV, suggesting that full dissociation of the water has been achieved. The pumping current of the sensor is linear as a function of water concentration for Vs = 1080 mV. The application of this technology to measure ambient humidity on-board a vehicle during fuel cut will be discussed. Figure 1

Sensitivity of surface temperature to radiative forcing by contrail cirrus in a radiative-mixing model

Abstract. Earth's surface temperature sensitivity to radiative forcing (RF) by contrail cirrus and the related RF efficacy relative to CO2 are investigated in a one-dimensional idealized model of the atmosphere. The model includes energy transport by shortwave (SW) and longwave (LW) radiation and by mixing in an otherwise fixed reference atmosphere (no other feedbacks). Mixing includes convective adjustment and turbulent diffusion, where the latter is related to the vertical component of mixing by large-scale eddies. The conceptual study shows that the surface temperature sensitivity to given contrail RF depends strongly on the timescales of energy transport by mixing and radiation. The timescales are derived for steady layered heating (ghost forcing) and for a transient contrail cirrus case. The radiative timescales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Without mixing, a large part of the energy induced into the upper troposphere by radiation due to contrails or similar disturbances gets lost to space before it can contribute to surface warming. Because of the different radiative forcing at the surface and at top of atmosphere (TOA) and different radiative heating rate profiles in the troposphere, the local surface temperature sensitivity to stratosphere-adjusted RF is larger for SW than for LW contrail forcing. Without mixing, the surface energy budget is more important for surface warming than the TOA budget. Hence, surface warming by contrails is smaller than suggested by the net RF at TOA. For zero mixing, cooling by contrails cannot be excluded. This may in part explain low efficacy values for contrails found in previous global circulation model studies. Possible implications of this study are discussed. Since the results of this study are model dependent, they should be tested with a comprehensive climate model in the future.

Aerodecelerator Performance of Flare-Type Membrane Inflatable Vehicle in Suborbital Reentry

A flight experiment of an inflatable reentry vehicle, equipped with a thin-membrane aeroshell deployed by an inflatable torus structure, was performed using a Japan Aerospace Exploration Agency S-310-41 sounding rocket. The drag coefficient history was evaluated by analyzing the acceleration of the vehicle with the atmospheric density and temperature using a global reference atmospheric model. The vehicle successfully demonstrated deceleration. During the reentry flight, the position, velocity, and acceleration of the vehicle were obtained by using the Global Positioning System. The experimental drag coefficient had an almost constant value of 1.5 in the supersonic region but decreased to 1.0 in the subsonic region. In the transonic region, a steep decrease of the drag coefficient was confirmed. To study the detailed aerodynamics for the reentry vehicle, flowfield simulations were conducted with computational fluid dynamics techniques. The aerodynamic force acting on the vehicle was investigated with the measured data throughout the supersonic and subsonic regions. In the flowfield simulation, the computed result for the drag coefficient showed reasonable agreement with the experimental one. In addition, a compressible effect in front of the vehicle was seen to appear in the supersonic region and a vortex ring at the rear of the vehicle was formed in the subsonic region.

Controlling 212Bi to 212Pb activity concentration ratio in thoron chambers

It is necessary to establish a reference atmosphere in a thoron chamber containing various ratios of 212Bi to 212Pb activity concentrations (C(212Bi)/C(212Pb)) to simulate typical environmental conditions (e.g., indoor or underground atmospheres). In this study, a novel method was developed for establishing and controlling C(212Bi)/C(212Pb) in a thoron chamber system based on an aging chamber and air recirculation loops which alter the ventilation rate. The effects of main factors on the C(212Bi)/C(212Pb) were explored, and a steady-state theoretical model was derived to calculate the ratio. The results show that the C(212Bi)/C(212Pb) inside the chamber is mainly dependent on ventilation rate. Ratios ranging from 0.33 to 0.83 are available under various ventilation. The stability coefficient of the ratios is better than 7%. The experimental results are close to the theoretical calculated results, which indicates that the model can serve as a guideline for the quantitative control of C(212Bi)/C(212Pb).

Rayleigh Lidar observed atmospheric temperature characteristics over a western Indian location: intercomparison with satellite observations and models

General characteristics of sub-tropical middle atmospheric temperature structure over a high altitude station, Mt. Abu (24.5°N, 72.7°E, altitude ~1670 m, above mean sea level (amsl)) are presented using about 150 nights observational datasets of Rayleigh Lidar. The monthly mean temperature contour plot shows two distinct maxima in the stratopause region (~45–55 km), occurring during February-March and September-October, a seasonal dependence similar to that reported for mid- and high-latitudes respectively. Semi-Annual Oscillation (SAO) are stronger at an altitude ~60 km in the mesospheric temperature in comparison to stratospheric region. A comparison with the satellite (Halogen Occultation Experiment, (HALOE)) data shows qualitative agreement, but quantitatively a significant difference is found between the observation and satellite. The derived temperatures from Lidar observations are warmer ~2–3 K in the stratospheric region and ~5–10 K in the mesospheric region than temperatures observed from the satellite. A comparison with the models, COSPAR International Reference Atmosphere (CIRA)-86 and Mass Spectrometer Incoherent Scatter Extended (MSISE)-90, showed differences of ~3 K in the stratosphere and ~5–10 K in the mesosphere, with deviations somewhat larger for CIRA-86. In most of the months and in all altitude regions model temperatures were lower than the Lidar observed temperature except in the altitude range of 40–50 km. MSISE-90 Model temperature overestimates as compared to Lidar temperature during December-February in the altitude region of 50–60 km. In the altitude region of 55–70 km both models deviate significantly, with differences exceeding 10–12 K, particularly during equinoctial periods. An average heating rate of ~2.5 K/month during equinoxes and cooling rate of ~4 K/month during November-December are found in altitude region of 50–70 km, relatively less heating and cooling rates are found in the altitude range of 30–50 km. The stratospheric temperature derived from the Lidar and columnar ozone observed by the Total Ozone Mapping Spectrometer (TOMS) over Mt. Abu shows good correlation (r 2 = 0.61) and indicates the association of ozone with the temperature.

The thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles

The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and multi-probe missions in the 1980s. The instruments on the recent Venus Express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the Venus atmosphere from 40 km to about 180 km altitude from April 2006 to November 2014. Many ground based experiments have provided data on the upper atmosphere (90–130 km) temperature structure since the publication of VIRA in 1985. The "Thermal Structure of the Venus Atmosphere" Team was supported by the International Space Studies Institute (ISSI), Bern, Switzerland, from 2013 to 2015 in order to combine and compare the ground-based observations and the VEx observations of the thermal structure as a first step towards generating an updated VIRA model. Results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry. The intercomparison of the ground-based and VEx results provides for the first time a consistent picture of the temperature and density structure in the 40 km–180 km altitude range. The Venus Express observations have considerably increased our knowledge of the Venus atmospheric thermal structure above ∼40 km and provided new information above 100 km. There are, however, still observational gaps in latitude and local time above certain regions. Considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present, such as a succession of warm and cool layers. Preliminary modeling studies support the existence of such layers in agreement with a global scale circulation. The intercomparison focuses on average profiles but some VEx experiments provide sufficient global coverage to identify solar thermal tidal components.The differences between the VEx temperature profiles and the VIRA below 0.1 mbar/95 km are small. There is, however, a clear discrepancy at high latitudes in the 10–30 mbar (70–80 km) range. The VEx observations will also allow the improvement of the empirical models (VTS3 by Hedin et al., 1983 and VIRA by Keating et al., 1985) above 0.03 mbar/100 km, in particular the 100–150 km region where a sufficient observational coverage was previously missing. The next steps in order to define the updated VIRA temperature structure up to 150 km altitude are (1) define the grid on which this database may be provided, (2) fill what is possible with the results of the data intercomparison, and (3) fill the observational gaps. An interpolation between the datasets may be performed by using available General Circulation Models as guidelines.An improved spatial coverage of observations is still necessary at all altitudes, in latitude–longitude and at all local solar times for a complete description of the atmospheric thermal structure, in particular on the dayside above 100 km. New in-situ observations in the atmosphere below 40 km are missing, an altitude region that cannot be accessed by occultation experiments. All these questions need to be addressed by future missions.

Semi-empirical thermosphere model evaluation at low altitude with GOCE densities

Aims : The quality of the Committee on Space Research (COSPAR) International Reference Atmosphere models NRLMSISE-00, JB2008, and DTM2013 in the 150–300 km altitude range has never been thoroughly evaluated due to a lack of good density data. This study aims at providing the model accuracies thanks to the recent high-resolution high-accuracy Gravity field and steady-state Ocean Circulation Explorer (GOCE) density dataset. The evaluation was performed on yearly, monthly, and daily time scales, which are important for different applications such as mission design, mission operation, or re-entry predictions. Methods : The accuracy of the models was evaluated by comparing to the GOCE density observations of the Science Mission (1 November 2009–20 October 2013) and new density data at the lowest altitudes derived for the last weeks before the re-entry (22 October–8 November 2013) according to a metric, which consists of computing mean, standard deviation and root mean square (RMS) of the observed-to-model ratios, and correlation. Mean statistics are then calculated over the three time scales. Results : The range of model biases, standard deviations, and correlations becomes larger when the time interval decreases, and this study provides COSPAR International Reference Atmosphere (CIRA) model statistics in the altitude range of 275–170 km. DTM2013 is the least biased and most accurate model on all time scales, essentially thanks to the database, notably containing two years of GOCE densities, to which it was fitted. NRLMSISE-00 performs worst, with considerable bias of about 20% in 2009 and 2013, and systematically higher standard deviations (lower correlations) than JB2008 and DTM2013. The performance of JB2008 is presently only slightly behind DTM2013, thanks to the new release 4_2g solar activity proxies. However, it still presents some weakness under the lowest solar activity conditions in 2009 and 2010. Comparison to Challenging Mini-Satellite Payload (CHAMP) density data showed that the results based on GOCE densities, despite limited local solar time coverage of 6–8 am & pm, are representative of model performance.