Impacts of the diurnal cycle of solar radiation on spiral rainbands

Based on idealized numerical simulations, the impacts of the diurnal cycle of solar radiation on the diurnal variation of outer rainbands in a tropical cyclone are examined. It is found that cold pools associated with precipitation-driven downdrafts are essential for the growth and propagation of spiral rainbands. The downdrafts result in surface outflows, which act as a lifting mechanism to trigger the convection cell along the leading edge of the cold pools. The diurnal cycle of solar radiation may modulate the diurnal behavior of the spiral rainbands. In the daytime, shortwave radiation will suppress the outer convection and thus weaken the cold pools. Meanwhile, the limited cold pool activity leads to a strong modification of the moisture field, which in turn inhibits further convection development.     

广州市雷暴日异常的基本气候特征及其与近海海温关系初探

以低纬高原城市昆明为研究对象，利用城市区域内4月、8月、12月的太阳辐射观测资料，对城市区域内不同下垫面性质和位置差异的辐射平衡特征和变化规律进行了研究。结果表明：昆明地区4月的太阳辐射各分量均较高，而多云天气的8月太阳辐射分量较小；屋顶的总辐射量和净辐射量均维持较高的数值，而受周围环境、建筑物遮蔽等影响的草地和球场则数值变化较大；随时间和下垫面的不同，反射辐射呈现较大差异；有效辐射则在多云天的8月呈现较小值(分配率趋于0)。所得结果可为探讨城市气候形成机制及城市气候的深入研究提供依据，并为其它地区的研究提供参考。     

Radiative cooling within illuminated layers of dust on (pre)-planetary surfaces and its effect on dust ejection

Temperature gradients in dust beds embedded in a low pressure gaseous environment induce a lift of particles under certain conditions. This effect can erode planetesimals and enables entrainment of dust into the martian atmosphere. Here, we consider a numerical model to calculate the temperature profile in a dust bed which is subject to illumination. We consider the situation when the illumination is switched on and heats the dust bed’s surface and when it is switched off again after a certain time. The calculations focus on the heat transfer by infrared radiation within the dust layer. We find that radiative transfer within the dust bed modifies the absolute temperatures and temperature gradients significantly. This is important for effects which are sensitive to absolute temperatures, i.e. ice sublimation or melting of solids. For low thermal conductivity dust beds of 0.001 W m⁻¹ K⁻¹ it determines the temperature structure of the dust. For higher thermal conductivities the modifications are moderate with respect to dust eruptions as the order of magnitude of temperature gradients stays the same.     

A Research on the Characteristics of Light Variation of Blazar 3C 273 in 2-10 keV

From the original observed data of RXTE (Rossi X-ray timing explorer), the data of 3C 273 in the X-ray band of 2-10 keV from February 2, 1996 (MJD 50115) to August 27, 2007 (MJD 54339) are analyzed. The photon spectral indexes and corresponding fluxes of the observational data from 1010 observations are obtained in total. The average time of each observation is 1666.76 seconds. By analyzing the spectral variation and behavior of the light variation of 3C 273 in the hard X-ray band of 2-10 keV during observational periods, it is found that there was a significant anti-correlation between the photon spectral index Γ and flux lgF_{2∼10 keV} in February 2000, March and April 2003, February, March and July 2004, as well as 2006 and 2007. During the observational periods in 1999 and from 2000 to 2007, there was also a significant anti-correlation between the monthly average behaviors of Γ and lgF_{2∼10 keV}. From the quantitative analysis of the behavior of light variation in the entire observational period, several relatively large light variations are found. The evidence of the existence of the Fe emission line with average width of 93.85±21.49 eV is also found by fitting a part of the spectra. Through analyzing the intensity of the light variation and features of Fe emission line, it is found that 3C 273 has some characteristics of blazars and Seyfert galaxies simultaneously.     

磁星能量注入模型拟合伽玛射线暴X射线余辉光变曲线

某些伽玛射线暴(简称伽玛暴)的中心致密天体可能是一颗具有强磁场的毫秒脉冲星,它通过磁偶极辐射可对伽玛暴外激波注入能量,从而导致早期余辉光变曲线的变平.近年来,从Swift卫星观测到的大量伽玛暴X射线余辉中发现,很多X射线余辉光变曲线在暴后10~2～10~4s期间的确存在明显的变平现象.利用周期为毫秒量级的磁星能量注入模型对11个加玛暴的X射线余辉光变曲线进行了拟合,显示该模型在解释余辉变平现象上的有效性和广泛性,通过对余辉光变曲线的拟合,同时也给出了相关中心磁星的磁场强度和旋转周期.     

CN rotational excitation

We demonstrate, using a sample of high quality spectra, that the average equivalent width ratio of the unsaturated R(0) and R(1) lines of the CN B²Σ⁺ – X²Σ⁺ (0, 0) band near 3875 Å equals π instead of 3.73 – calculated for the CMBR temperature T = 2.725 K and the already published oscillator strengths of both transitions, i.e. the excitation temperature of CN is slightly higher than it should be expected if CMBR is the only excitation mechanism. Taking into account the saturation effects by means of profile fitting during the column density calculations does not remove the revealed temperature excess. Possible interpretations of the effect are discussed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analytical Afterglow Light Curves of Gamma-ray Bursts: the Case of a Flat Electron Spectrum

In the standard afterglow model, the swept electrons have a single power-law energy distribution dn/dγe ∝ γ−p e (p ∼ 2.3), owing to the first order Fermi acceleration process. However, in some events people find a lot of evidence for a flat electron spectrum (i.e., p < 2). In this work, the analytical afterglow light curves in the case of a flat electron energy distribution are presented respectively for a single power-law spectrum and a broken power-law spectrum, then the results are applied to the specific burst GRB 060908. Besides, we have also speculated a possible solution of the so-called low energy spectrum crisis of Gamma-ray Bursts     

Simulation Studies for Faraday Rotation Measure Observations

Limited by the spatial resolution of a radio telescope, multiple sources may be overlapped in the observing direction of the telescope. The Faraday rotation measure (RM) and polarization angle (PA) measurements of a target radio source will be affected by the other background radio sources located in the directional beam. The simulation study indicates that the influence of background radio sources on the polarization measurement of the target source depends on the RM values of interference sources. The RM value obtained by fitting the data of polarization observations at 2 or 3 wavelengths is not reliable. To obtain the accurate RM value of the target source needs to make fitting on the Stokes parameters Q and U observed at multiple wavebands.     

Validation and calibration of solar radiation equations for estimating daily reference evapotranspiration at cool semi-arid and arid locations

ABSTRACT

In this work, the applicability of 12 solar radiation (R_S) estimation models and their impacts on daily reference evapotranspiration (ET_o) estimates using the Penman‐Monteith FAO-56 (PMF-56) method were tested under cool arid and semi-arid conditions in Iran. The results indicated that the average increase in accuracy of the ET_o estimates by the calibrated R_S models, quantified by the decrease in RMSE, was 2.8% and 6.4% for semi-arid and arid climates, respectively. Mean daily deviations in the estimated ET_o by the calibrated R_S equations in semi-arid climates varied from ?0.283?mm/d^-1 for the Glover‐McCulloch model to 0.080?mm/d for the El-Sebaii model, with an average of ?0.109?mm/d^-1, and in arid climates, they ranged from ?0.522?mm/d^-1 for the Samani model to 0.668?mm/d for the El-Sebaii model, with an average of 0.125?mm/d^-1.

Editor D. Koutsyiannis; Associate editor Not assigned