Optimal orbits for Mars atmosphere remote sensing

Most of the spacecrafts currently around Mars (or planned to reach Mars in the near future) use Sun-synchronous or near-polar orbits. Such orbits offer a very poor sampling of the diurnal cycle. Yet, sampling the diurnal cycle is of key importance to study Mars meteorology and climate. A comprehensive remote sensing data set should have been obtained by the end of the MRO mission, launched in 2005. For later windows, time-varying phenomena should be given the highest priority for remote sensing investigations. We present possible orbits for such missions which provide a rich spatial and temporal sampling with a relatively short repeat cycle (50 sols). After computation and determination of these orbits, said “optimal orbits”, we illustrate our results by tables of sampling and comparison with other orbits.     

Propagation of Alfvén waves in multi-layer solar atmosphere model

In this paper, we idealize the actual solar atmosphere as a multi-isothermal-layer system so as to obtain the energy transmittance of the linear Alfvén wave that propagates through such a system in presence of a uniform oblique magnetic filed. The results indicate that the two-layer model is essentially different to the three-layer one. In the two-layer model, the temperature jump acts as a high pass filter. In the three-layer model, resonant transfer will take place and the transmittance undergoes oscillation as the trigonometric function terms dominate its behavior. For actual solar atmosphere, the result reveals that the lower parts of solar atmosphere are more suitable for those Alfvén waves with period of seconds to transfer their energy.     

SWAS observations of water vapor in the Venus mesosphere

We present the first detections of the ground-state H₂¹⁶O (₁₁₀-₁₀₁) rotational transition (at 556.9 GHz) and the ¹³CO (5-4) rotational transition from the atmosphere of Venus, measured with the Submillimeter Wave Astronomy Satellite (SWAS). The observed spectral features of these submillimeter transitions originate primarily from the 70-100 km altitude range, within the Venus mesosphere. Observations were obtained in December 2002, and January, March, and July 2004, coarsely sampling one Venus diurnal period as seen from Earth. The measured water vapor absorption line depth shows large variability among the four observing periods, with strong detections of the line in December 2002 and July 2004, and no detections in January and March 2004. Retrieval of atmospheric parameters was performed using a multi-transition inversion algorithm, combining simultaneous retrievals of temperature, carbon monoxide, and water profiles under imposed constraints. Analysis of the SWAS spectra resulted in measurements or upper limits for the globally averaged mesospheric water vapor abundance for each of the four observation periods, finding variability over at least two orders of magnitude. The results are consistent with both temporal and diurnal variability, but with short-term fluctuations clearly dominating. These results are fully consistent with the long-term study of mesospheric water vapor from millimeter and submillimeter observations of HDO [Sandor, B.J., Clancy, R.T., 2005. Icarus 177, 129-143]. The December 2002 observations detected very rapid change in the mesospheric water abundance. Over five days, a deep water absorption feature consistent with a water vapor abundance of 4.5±1.5 parts per million suddenly gave way to a significantly shallower absorption, implying a decrease in the water vapor abundance by a factor of nearly 50 in less that 48 h. In 2004, similar changes in the water vapor abundance were measured between the March and July SWAS observing periods, but variability on time scales of less than a week was not detected. The mesospheric water vapor is expected to be in equilibrium with aerosol particles, primarily composed of concentrated sulfuric acid, in the upper haze layers of the Venus atmosphere. If true, moderate amplitude (10-15 K) variability in mesospheric temperature, previously noted in millimeter spectroscopy observations of Venus, can explain the rapid water vapor variability detected by SWAS.     

Low latitude airglow

Tropical airglow work during the last few years is reviewed. Airglow instrumentation is becoming more complex. Some of these sophisticated airglow experiments giving important information about the upper atmosphere such as ionospheric F region electron density, height of maximum electron density, dynamics of and irregularities in the F region, mesospheric neutral temperature and its variation, dynamics of mesospheric, etc. are mentioned. At the end some problems which could be tackled in near future with airglow techniques have been suggested. Invited Review paper, Commission 21, IAU, Patras, Greece, August, 1982.     

The Boussinesq-BO equation for algebraic gravity solitary waves in baroclinic atmosphere and the research of squall lines formation mechanism

The gravity solitary waves are a kind of waves which are caused by the disturbance of static equilibrium. The nonlinearity concentration of the gravity solitary waves makes the energy assemble together and forms disastrous weather phenomena, such as squall lines. By the calculation condition and theoretical method limit, previous studies tried hard to reduce the variable numbers and discussed the gravity solitary waves in barotropic atmosphere, but the baroclinic problem of atmosphere is inevitable topic. In this paper, from the basic kinetic equations in baroclinic non-static equilibrium atmosphere, by using multi-scale analysis and perturbation method, a new model is derived to describe the algebraic gravity solitary waves, we call it Boussinesq-BO equation. Comparing with the former models, the Boussinesq-BO model can describe the propagation process of waves in two directions and is more suitable for the real atmosphere condition. With the help of the trial function method, an exact solution of Boussinesq-BO equation is obtained and the fission property of algebraic gravity solitary waves is discussed. Finally, we can find that the fission of algebraic gravity solitary waves is also a possible formation mechanism of squall lines.     

Mapping of Ozone and Water in the Atmosphere of Mars near the 1997 Aphelion

We present absolute abundances and latitudinal variations of ozone and water in the atmosphere of Mars during its late northern spring (L_s=67.3°) shortly before aphelion. Long-slit maps of the a¹Δ_g state of molecular oxygen (O₂) and HDO, an isotopic form of water, were acquired on UT January 21.6 1997 using a high-resolution infrared spectrometer (CSHELL) at the NASA Infrared Telescope Facility. O₂(a¹Δ_g) is produced by ozone photolysis, and the ensuing dayglow emission at 1.27 μm is used as a tracer for ozone. Retrieved vertical column densities for ozone above ∼20 km ranged between 1.5 and 2.8 μm-atm at mid- to low latitudes (30°S-60°N) and decreased outside that region. A significant decrease in ozone density is seen near 30°N (close to the subsolar latitude of 23.5°N). The rotational temperatures retrieved from O₂(a-X) emissions show a mean of 172±2.5 K, confirming that the sensed ozone lies in the middle atmosphere (∼24 km). The ν₁ fundamental band of HDO near 3.67 μm was used as a proxy for H₂O. The retrieved vertical column abundance of water varies from 3 precipitable microns (pr-μm) at ∼30°S to 24 pr-μm at ∼60°N. We compare these results with current photochemical models and with measurements obtained by other methods.     

CO2 processes in an alpine grassland ecosystem on the Tibetan Plateau

In this paper, the CO2 concentrations profile from 1.5 m depth in soil to 32 m height in atmosphere were measured from July 2000 to July 2001 in an alpine grassland ecosystem located in the permafrost area on the Tibetan Plateau, which revealed that CO2 concentrations varied greatly during this study period. Mean concentrations during the whole experiment in the atmosphere were absolutely lower than the CO2 concentrations in soil, which resulted in CO2 emissions from the alpine steppe soil to the atmosphere. The highest CO2 concentration was found at a depth of 1.5 m in soil while the lowest CO2 concentration occurred in the atmosphere. Mean CO2 concentrations in soil generally increased with depth. This was the compositive influence of the increasing soil moistures and decreasing soil pH, which induced the increasing biological activities with depth. Temporally, the CO2 concentrations at different layers in air remained a more steady state because of the atmospheric turbulent milking. During the seasonal variations, CO2 concentrations at surface soil interface showed symmetrical patterns, with the lowest accumulation of CO2 occurring in the late winter and the highest CO2 concentration in the growing seasons.     

Detection of a southern peak in Mercury's sodium exosphere with the TNG in 2005

A long term plan of observations of the sodium exosphere of Mercury began in 2002 by using the high resolution echelle spectrograph SARG and a devoted sodium filter at the 3.5 m Galileo National Telescope (TNG) located in La Palma, Canary Islands. This program is meant to investigate the variations of the sodium exosphere appearance under different conditions of observations, namely Mercury's position along its orbit, phase angle and different solar conditions, as reported by previous observations in August 2002 and August 2003 [Barbieri, C., Verani, S., Cremonese, G., Sprague, A., Mendillo, M., Cosentino, R., Hunten, D., 2004. Planet. Space Sci. 52, 1169-1175; Leblanc, F., Barbieri, C., Cremonese, G., Verani, S., Cosentino, R., Mendillo, M., Sprague, A., Hunten, D., 2006. Icarus 185 (2), 395-402].Here we present the analysis of data taken in June 29th and 30th and in July 1st 2005, when Mercury's true anomaly angle (TAA) was in the range 124-130°. The spectra show particularly intense sodium lines with a distinctive peak in emission localized in the southern hemisphere at mid-latitudes. This seems to be a persistent feature related to consecutive favorable IMF conditions inducing localized enhancements of surface sodium density. The comparison with previous data taken by Potter et al. [Potter, A.E., Killen, R.M., Morgan, T.H., 2002. Meteorit. Planet. Sci. 37 (9), 1165-1172] evidences a surprising consistency of the anti-sunward component, which appears to remain constant regardless of the changing illumination and space weather conditions at Mercury.     

Microwave observations of Saturn's rings: anisotropy in directly transmitted and scattered saturnian thermal emission

We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae.     

白天工作条件下大气激光雷达探测的实验研究

作者在已完成大气激光雷达系统夜间工作的基础上 ,对白天工作条件下的各种环境背景光的干扰进行了理论与实验分析 ,得出太阳直射光和天空光为白天工作的主要背景干扰。实验结果表明 ,经过激光发射与接收视场角严格匹配及使用干涉滤光器 (2 .6 nm和 0 .15nm)进行窄带滤波 ,背景干扰被明显地剔除 ,可进一步压低背景干扰约 2 0倍。证明采取视场匹配及干涉滤光器的措施可基本保证激光雷达系统在白天条件下工作。