Parameterization of key optical and radiative characteristics of homogeneous layers of mixed phase clouds

Key optical characteristics of radiation scattering in clouds (mean cosine of the scattering phase function, averaged factors and indices of scattering efficiency, and single-scattering albedo) and integral characteristics of homogeneous cloud layers (cloud-layer albedo and transmission factor) have been calculated with the use of the earlier suggested model of the microstructure of mixed phase clouds, where ice crystals and water droplets are homogeneously mixed over the volume, for individual wavelengths in the range from 0.6 to 10.6 μm. An approach is elaborated for statistically valid parameterization of the above characteristics versus the mean temperature of a mixed layer only under the availability of reliable information about the temperature dependence of the characteristic sizes of particles of different fractions and their concentrations in the cloud.     

辽东湾冰季太阳辐射分析

利用渤海辽东湾ＪＺ２０－２石油平台上的气象和海冰观测数据,研究了冰季大气层和云层对太阳辐射的影响,结果表明,辽东湾冰季大气光学可取为０．８３,碧空、少云、多云阴天、雾天和雨雪等不同天气条件下的云量系数可分别取为０、３、６、８、９和１０。分析了冰水混合情况下海面对太阳辐射的反射情况;讨论了太阳辐射对冰面长波辐射和对流传热的影响。利用冰面太阳辐射的实测值和计算结果,对整个冰季内太阳辐射的规律进行了分析     

渤海平整海冰多角度反射光谱特征

近些年来,遥感技术在渤海海冰的监测中发挥了举足轻重的作用。海冰的反射特征是利用光学遥感监测海冰的基础。在晴空条件下,对盛冰期渤海辽东湾东部3种典型的平整海冰的半球-方向反射率因子(hemispherical directional reflectance factor,HDRF)进行了测量,并计算了相应的各向异性因子(anisotropy factor,ANIF),结果表明,只有在太阳光入射主平面内的前向反射方向附近,半球-方向反射率因子与各向异性因子才会迅速增加,而在其他方向上两者的变化不明显。平整海冰的厚度和内部结构等因素会影响HDRF和ANIF随波长变化的特征,在350~1 350 nm波段,厚度较小且表面光滑的平整海冰的HDRF值相对较小,而厚度较大的平整海冰的HDRF值相对较大。在350~950 nm波段,厚度较小且表面光滑的平整海冰ANIF相对较大,而厚度较大的平整海冰的ANIF值相对较小。以上结果充分说明海冰对太阳光入射辐射的反射是冰-气界面的反射与冰体内部的散射的综合结果。     

海冰对北极海冰边缘区大洋光学观测的影响评估

Diffuse attenuation coefficient(DAC) of sea water is an important parameter in ocean thermodynamics and biology, reflecting the absorption capability of sea water in different layers. In the Arctic Ocean, however, sea ice affects the radiance/irradiance measurements of upper ocean, which results in obvious errors in the DAC calculation. To better understand the impacts of sea ice on the ocean optics observations, a series of in situ experiments were carried out in the summer of 2009 in the southern Beaufort Sea. Observational results show that the profiles of spectral diffuse attenuation coefficients of seawater near ice cover within upper surface of 50 m were not contaminated by the sea ice with a solar zenith angle of 55°, relative azimuth angle of 110°≤φ≤115° and horizontal distance between the sensors and ice edge of greater than 25 m. Based on geometric optics theory, the impact of ice cover could be avoided by adjusting the relative solar azimuth angle in a particular distance between the instrument and ice. Under an overcast sky, ice cover being 25 m away from sensors did not affect the profiles of spectral DACs within the upper 50 m either. Moreover, reliable spectral DACs of seawater could be obtained with sensors completely covered by sea ice.     

Observation of clouds and solar radiation over the Pacific Ocean as relation to global climate

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Measuring solar irradiance profiles in the Arctic sea ice using fiber optic spectrometry via inclined holes

An irradiance profile measurement approach and profiling system were developed to measure the solar irradiance profile of the Arctic sea ice using fiber optic spectrometry. The approach involved using a miniature spectrometer to sense light signals collected and transmitted from a fiber probe. The fiber probe was small, and could thus move freely in inclined bore holes drilled in sea ice with its optical entrance pointing upward. The input-output relationship of the system was analyzed and built. Influence factors that determined the system output were analyzed. A correctional system output approach was proposed to correct the influence of these factors, and to obtain the solar irradiance profile based on the measurements outputted by this system. The overall performance of the system was examined in two ice floes in the Arctic during the 9 th Chinese National Arctic Research Expedition. The measured solar irradiance profiles were in good agreement with those obtained using other commercially available oceanographic radiometers. The derived apparent optical properties of sea ice were comparable to those of similar sea ice measured by other optical instruments.     

海冰热力模式的辐射参数化方案在渤海和波罗的海应用的比较

研究了海冰热力模式中的各种辐射参数化方案,对比了模式计算的太阳短波辐射、大气长波辐射以及海冰热力变化,并利用渤海和波罗的海观测资料进行比较和误差分析.冬季大部分时间太阳短波辐射对海冰热力过程的作用有限.简单计算方案一般满足海冰模式要求.误差主要受云和冰雪表面与大气之间的多重反射影响.长波辐射对表面热平衡和海冰质量变化起重要作用.长波辐射参数化方案的计算结果受环境因素影响.云量参数化有待进一步改进.海冰模式计算结果的精度与长波辐射计算精度有一致性.     

极低太阳高度条件下穿透海冰的太阳辐射研究

基于2007年冬季北极的透射辐射光学数据,研究了极低太阳高度条件下的太阳辐射特征。低太阳高度时较短波长的可见光受到削弱,而较长波长的光得以保留,呈现明显的双峰结构。由于考察时的海冰都是新冻结的当年冰,厚度小,积雪层很薄,海冰的反射率较低,有较高比例的太阳辐射进入海冰或海洋。没有积雪的冰面由于反射率随波长增加而减少,更高比例的长波进入海冰。但在透射辐射光谱中,490 nm的光重新占优势,较长波长的光在穿过海冰时受到很大的削弱。因此,在低太阳高度的条件下,较短波长的光在大气中受到显著削弱,而较长波长的光在海冰中受到显著削弱,大气和海冰共同作用的结果使进入冰下海水的太阳辐射能更加微弱。但是,海冰对较长波长光的吸收使海冰获取较多的热量,减缓海冰的冻结过程。     

气象条件对青岛地区气溶胶光学特性的影响

利用 2 0 0 2年 4月至 2 0 0 3年 10月多波段太阳光度计资料和同期的气象观测资料 ,分析了不同气象条件下青岛气溶胶光学特性的变化。气象条件的转变与青岛地区气溶胶光学特性之间具有很好的响应关系 :南风盛行时会加大光学厚度 ,并增强气溶胶对 >5 0 0nm波段太阳辐射的散射能力 ;轻雾和霾在青岛气溶胶光学厚度中占有较大比重 ,而霾对 <5 0 0nm波段辐射的散射能力较强。     

Asymmetry parameter of the optical scattering phase function of a mixed-phase cloud

Basic characteristics of optical scattering in a mixed-phase cloud (asymmetry parameter of the scattering phase function and efficiency scattering factors and scattering coefficients) are considered. Theoretical consideration is based on the mixed-phase cloud model in the form of a uniform mixture of ice crystals and water droplets. Expressions allowing calculation of asymmetry parameter of the mixed-phase cloud scattering phase function are obtained as functions of the cloud temperature, average size of cloud particles, and ratios of the number densities of differently shaped ice crystals. Data calculated for the asymmetry parameter of infrared scattering in a mixed-phase cloud layer at its given temperature are presented.     

Possibilities of using optical spectral analysis to estimate characteristics of roughness in the presence of films on the sea surface

The possibility of using an optical spectrum analyzer (OSA) to determine the degree of short gravity-capillary wave damping by films of surface-active substances (SAS) is studied. Nonlinear mechanisms of optical surface imaging associated with a complex profile of sky brightness and long waves are analyzed. Using the model of free short gravity waves damping by the films, it is shown that the difference between the contrast of roughness and imaging in film-covered surface regions can be substantial and attributed to a variability of the damping degree within a specified wavelength range rather than to the wave-damping value. In addition, it is illustrated that Doppler shifts of the OSA space-time spectrum in regions covered with films can substantially increase due to nonlinear distortions of the surface images. This fact should be taken into account when obtaining additional information on the state of the surface and roughness based on the Doppler shift values.     

Inter-comparisons of thermodynamic sea-ice modeling results using various parameterizations of radiative flux

1 Introduction The solar and terrestrial radiations are the major energy sources and sinks for the earth climate system. Climatologically, in high latitudes and polar regions, the radiative fluxes are often an order of magnitude larger than the other surf…     

2001—2017年北极秋季低云变化及其可能原因

本文通过对2001—2017年秋季北极低云的多源数据的分析,展示了本世纪以来北极秋季低云的变化,并为其变化提供了一个新的可能的解释。卫星和再分析数据表明,秋季北极有冰海面低云存在减少的趋势,且在北极边缘海区表现为950 hPa(约500 m)以下近地面云显著减少。本文研究表明,在有冰海面上,低云减少的趋势与背景大气增暖导致的大气相对湿度降低有关,这一关系在80°N以北的北极中央区更明显。而在北极边缘海区,气旋活动对云的影响更重要。在有冰海面,气旋与低云的长期变化趋势相反,两者的年际变化呈负相关关系。利用自组织映射(SOM,Self-Organizing Map)对所有气旋日垂直运动和云分布进行了初步分析,结果表明:在无冰海面和有冰海面由于气旋垂直运动及背景(无气旋日)云分布的差异,气旋对云的影响存在差异。气旋在有冰海面导致低云减少为主,而在无冰海面导致低云增加为主。     

夏季北极海冰表皮温度实测资料与MODIS产品的对比分析

Ship-borne infrared radiometric measurements conducted during the Chinese National Arctic Research Expedition(CHINARE) in 2008, 2010, 2012, 2014, 2016 and 2017 were used for in situ validation studies of the Moderate Resolution Imaging Spectroradiometer(MODIS) sea ice surface temperature(IST) product.Observations of sea ice were made using a KT19.85 radiometer mounted on the Chinese icebreaker Xuelong between July and September over six years. The MODIS-derived ISTs from the satellites, Terra and Aqua, both show close correspondence with ISTs derived from radiometer spot measurements averaged over areas of 4 km×4 km, spanning the temperature range of 262–280 K with a ±1.7 K(Aqua) and ±1.6 K(Terra) variation. The consistency of the results over each year indicates that MODIS provides a suitable platform for remotely deriving surface temperature data when the sky is clear. Investigation into factors that cause the MODIS IST bias(defined as the difference between MODIS and KT19.85 ISTs) shows that large positive bias is caused by increased coverage of leads and melt ponds, while large negative bias mostly arises from undetected clouds. Thin vapor fog forming over Arctic sea ice may explain the cold bias when cloud cover is below 20%.     

Dual-polarized ratio algorithm for retrieving Arctic sea ice concentration from passive microwave brightness temperature

We present a new algorithm for retrieving sea ice concentration from the AMSR-E data, the dual-polarized ratio (DPR) algorithm. The DPR algorithm is developed using vertically and horizontally polarized brightness temperatures at the same channel of 36.5 GHz. It depends on the ratio of dual-polarized emissivity, α, which is determined empirically at about 0.92 by remotely sensed brightness temperature in winter and used for the other seasons as well. The ice concentration retrieved by the DPR is compared with those by the NT2 and ABA algorithms. Since the main difference among these algorithms takes place in marginal ice zones, 17 marginal ice zones are chosen. The retrieved ice concentrations in these zones are examined by the ice concentration obtained by the MODIS data. The mean error, root-mean-square error and mean absolute error of the DPR algorithm are relatively better than those from the other two algorithms. The results of this study illustrate that the DPR algorithm is a more accurate algorithm for retrieving sea ice concentration from the AMSR-E brightness temperature, and can be used for operational purposes.     

微型近红外光谱仪测量北极积雪覆盖海冰内部太阳辐照度可行性研究

The extremely low temperature, high humidity and limited power supply pose considerable challenges when using spectrometers within the Arctic sea ice. The feasibility of using a miniature low-power near-infrared spectrometer module to measure solar radiation in Arctic sea ice environments was investigated in this study.Temperature and integration time dependences of the spectrometer module were examined over the entire target operating range of –50℃ to 30℃, well below the specified operating range of this spectrometer. Using these observations, a dark output prediction model was developed to represent dark output as a function of temperature and integration time. Temperature-induced biases in the saturation output and linear operating range of the spectrometer were also determined. Temperature and integration time dependences of the signal output were evaluated. Two signal output correction models were developed and compared, to convert the signal output at any temperature within the operating temperature range and integration time to that measured at the reference temperature and integration time. The overall performance of the spectrometer was evaluated by integrating it into a refined fiber optic spectrometry system and measuring solar irradiance distribution in the ice cover with thickness of 1.85 m in the Arctic during the 9th Chinese National Arctic Research Expedition. The general shape of the measured solar irradiance above the snow surface agreed well with that measured by other commercial oceanographic spectroradiometers. The measured optical properties of the sea ice were generally comparable to those of similar ice measured using other instruments. This approach provides a general framework for assessing the feasibility of using spectrometers for applications in cold environments.     

影响海洋光学遥感的海面白泡云研究回顾及进展

回顾了国内外影响海洋光学遥感的白泡云的反射率和覆盖率的研究进展情况。根据海洋水色高光谱遥感发展的需要，指出应当开展海洋白泡云中信号白浪和白沫光学反射特征的测量和研究，以便评价和排除白泡云的反射分量在光学遥感中的干扰。     

北极海冰密集度动态系点值ASI反演算法研究

海冰密集度是极区海冰监测的重要因素,使用AMSR-E (Advanced Microwave Scanning Radiometer for Earth Observing System) 89GHz数据ASI反演算法得到的海冰密集度是目前能够获得的分辨率最高的微波数据.在以前的算法中往往使用固定的系点值,本研究实现了动态系点值ASI (the Arctic Radiation And Turbulence Interaction Study (ARTIST) Sea Ice)算法,更重要的是在统计开阔水系点值的时候消除了云对系点值的影响,使得纯水系点值更接近真实状况.得到2010年平均的开阔水和海冰的系点值分别为50.8K和7.8K,通过每天的系点值得到的反演方程在低密集度区增大了海冰密集度,在高密集冰区减小了海冰密集度,从而在一定程度上改善了微波数据的反演准确度.通过和北极区域选取40幅不受云影响的MODIS 500m分辨率宽频大气层顶反照率(broadband TOA albedo)计算的海冰密集度进行了比较验证.结果显示,40个个例中,95%本文的平均差异比使用固定系点值算法产品的小,而且75%的均方根差异比使用固定系点值算法产品的小.     

Influence of sea roughness and atmospheric inhomogeneities on microwave radiation of the atmosphere-ocean system

A discussion of the influence of sea roughness and spatial atmospheric inhomogeneities on the precision of satellite microwave radiometric measurements of the atmospheric parameters is presented. The two-scale model for microwave radiation of the ruffled sea surface without foam and spray is confirmed by experimental measurements. Investigations of the brightness temperature fluctuations of the clear and cloudy atmosphere are made using aircraft experimental measurements at the wavelengths 0.8 and 1.35 cm. Calculations of the radiation averaged over a satellite antenna footprint are carried out on the basis of these results and of well-known results of optical and infrared measurements. It is shown that sea roughness and the nonuniformity of clouds may result in errors in the integrated atmosphere water vapor and cloud liquid water content determination by satellite two-wavelength (0.8 and 1.35 cm) radiometric measurements up to 30 and 70 percent, respectively.     

Optical properties and surface energy flux of spring fast ice in the Arctic

Over the past decades, sea ice in the polar regions has been significantly affecting local and even hemispheric climate through a positive ice albedo feedback mechanism. The role of fast ice, as opposed to drift ice, has not been well-studied due to its relatively small coverage over the earth. In this paper, the optical properties and surface energy balance of land fast ice in spring are studied using in situ observations in Barrow, Alaska. The results show that the albedo of the fast ice varied between 0.57 and 0.85 while the transmittance increased from 1.3×10?3 to 4.1×10?3 during the observation period. Snowfall and air temperature affected the albedo and absorbance of sea ice, but the transmittance had no obvious relationship with precipitation or snow cover. Net solar shortwave radiation contributes to the surface energy balance with a positive 99.2% of the incident flux, with sensible heat flux for the remaining 0.8%. Meanwhile, the ice surface loses energy through the net longwave radiation by 18.7% of the total emission, while the latent heat flux accounts for only 0.1%. Heat conduction is also an important factor in the overall energy budget of sea ice, contributing 81.2% of the energy loss. Results of the radiative transfer model reveal that the spectral transmittance of the fast ice is determined by the thickness of snow and sea ice as well as the amount of inclusions. As major inclusions, the ice biota and particulates have a significant influence on the magnitude and distribution of the spectral transmittance. Based on the radiative transfer model, concentrations of chlorophyll and particulate in the fast ice are estimated at 5.51 mg/m2 and 95.79 g/m2, which are typical values in the spring in Barrow.