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

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Influence of stratification and irradiance regime on summer phytoplankton composition in coastal and shelf seas of the British Isles

The effect of interaction between stratification and irradiance regimes on phytoplankton community structure was investigated in three shelf/coastal regions of the British Isles, each of which displayed ranges of vertical stability and light attenuation. Relationships between vertical stability, light penetration and community structure were indicated by the ordination of dominance (assessed using cell volume) of the main phytoplankton phyletic groups—diatoms, dinoflagellates and microflagellates—on a surface defined by a bulk stratification index () and water column depth, scaled by transparency (λh). Diatom- and dinoflagellate-dominated communities occupied distinctly different domains on the - λh surface, diatoms being favoured in well-mixed water columns with high values for λh and dinoflagellates dominating where stratification was strong and λh was low. Microflagellates were not abundant in any of the study areas and showed no clear ordination on the - λh surface. The domain of co-dominance of diatom and dinoflagellates on the - λh surface was narrow with small changes in the irradiance or stratification regime resulting in a switch to diatom or dinoflagellate dominance. It is suggested that loss of non-motile diatom communities in strongly stratified water columns might be a strong selective force in favour of dinoflagel-lates. However, in water columns with intermediate stratification and optical properties, the outcome of competition may be decided by physiological attributes of the two groups with respect to growth in low and fluctuating irradiances.     

A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss Alps

We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid‐latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon‐dated periods defined with less extensive glaciers coincide with periods of reduced radio‐production, pointing to a connection between solar activity and glacier melting processes. Measured long‐term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long‐term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances.     

Influence of the total atmospheric optical depth and cloud cover on solar irradiance components

Broadband solar irradiance data obtained in the spectral range 400–940 nm at Kwangju, South Korea from 1999–2000 have been analyzed to investigate the effects of cloud cover and atmospheric optical depth on solar radiation components. Results from measurements indicate that the percentage of direct and diffuse horizontal components of solar irradiance depend largely on total optical depth (TOD) and cloud cover. During summer and spring, the percentages of diffuse solar irradiance relative to the global irradiance were 5.0% and 4.9% as compared to 2.2% and 3.0% during winter and autumn. The diffuse solar irradiance is higher than the direct in spring and summer by 24.2%, and 40.6%, respectively, which may largely be attributed to the attenuation (scattering) of radiation by heavy dust pollution and large cloud amount. In cloud-free conditions with cloud cover ≤2/10, the fraction of the direct and diffuse components were 66.0% and 34.0%, respectively, with a mean daily global irradiance value of 7.92±2.91 MJ m⁻² day⁻¹. However, under cloudy conditions (with cloud cover ≥8/10), the diffuse and direct fractions were 97.9% and 2.2% of the global component, respectively. The annual mean TOD under cloudless conditions (cloud cover≤2/10) yields 0.74±0.33 and increased to as much as 3.15±0.67 under cloudy conditions with cloud amount ≥8/10. An empirical formula is derived for estimating the diffuse and direct components of horizontal solar irradiance by considering the total atmospheric optical depth (TOD). Results from statistical models are shown for the estimation of solar irradiance components as a function of TOD with sufficient accuracy as indicated by low standard error for each solar zenith angle (SZA).     

Diurnal variability in turbidity and coral fluorescence on a fringing reef flat: Southern Molokai,Hawaii

Terrigenous sediment in the nearshore environment can pose both acute and chronic stresses to coral reefs. The reef flat off southern Molokai, Hawaii, typically experiences daily turbidity events, in which trade winds and tides combine to resuspend terrigenous sediment and transport it alongshore. These chronic turbidity events could play a role in restricting coral distribution on the reef flat by reducing the light available for photosynthesis. This study describes the effects of these turbidity events on the Hawaiian reef coral Montipora capitata using in situ diurnal measurements of turbidity, light levels, and chlorophyll fluorescence yield via pulse-amplitude-modulated (PAM) fluorometry. Average surface irradiance was similar in the morning and the afternoon, while increased afternoon turbidity resulted in lower subsurface irradiance, higher fluorescence yield (ΔF/F_m^′), and lower relative electron transport rates (rETR). Model calculations based on observed light extinction coeffecients suggest that in the absence of turbidity events, afternoon subsurface irradiances would be 1.43 times higher than observed, resulting in rETR for M. capitata that are 1.40 times higher.     

Estimation of the <Emphasis Type="Italic">in situ</Emphasis> Ultraviolet-A absorption of seawater by a simple irradiance inversion model

An irradiance inversion model to estimate the in situ absorption coefficient of seawater has been developed for the Ultraviolet-A (UVA) wavelength domain. Input parameters are sun angle and the up-and downward planar irradiances measured for at least two depths. The present method does not require seawater to be sampled, and is a discrete wavelength method which returns the absorption coefficient at a given wavelength from the irradiances measured at that wavelength without assuming a spectral shape of any optical properties a priori. Comparison between the model results and spectrophotometric measurements shows that the model is practically useful when cloud cover in the atmosphere is ≤ 50%. According to the present method, measurements of the irradiances enable simultaneous observation of the in situ underwater UVA radiation level and the absorption capacity of bulk seawater using a radiometer.     

海面大气和海洋条件变化引起的太阳辐照度高频变化分析

海洋光学考察时需要同步测量大气中的下行太阳辐照度,其测量采样频率比常规大气辐射观测高300倍,可记录到达海面太阳辐射的高频变化。利用2007年在白令海考察的数据,详细研究了辐照度高频变化的特征与原因,得出影响辐照度记录的主要因素有云层、海雾和海浪。结果表明,这3种因素的影响有明显的差别,使作者有可能在不确切知道现场情况的条件下,由数据本身判断辐照度变化的原因,并获取有关的参数。云层引起的辐照度变化具有低频率、大振幅的特征。海雾引起的辐照度变化最为复杂,变化幅度大,变化周期复杂,从几秒到上百秒,与云层效应相区别。晴空条件下,海浪调制的反射信号通过空气中的水汽散射影响辐照度计测量数值,形成周期短、振幅小的稳定振动信号,与云和雾的效应有明显区别。文中提供了云、雾和浪对辐照度影响的定性特征和定量分析结果,对理解海面辐照度记录,并正确处理数据有指导意义。     

光照强度对隐藻吸收铁和磷的影响

在模拟条件下,通过深入研究光照强度对隐藻生长率的影响,以及不同光照强度下藻细胞对Fe和P的吸收差异,提出了光照强度控制藻细胞对营养元素的吸收,最终限制赤潮藻爆发性增殖的作用途径.研究表明,藻细胞的生长率与光照强度之间呈指数相关关系;隐藻生长的光饱和值与光半饱和值分别为150 μmol/(m2·s)和47 μmol/(m2·s);在低光照强度下藻细胞的生长率较低,但是藻细胞却需要吸收更多的Fe和P,以及Zn、Mn、Co和Mo等微量元素,在光照强度为10 μmol/(m2·s)时,藻细胞生长率仅为光照强度150 μmol/(m2·s)时的十分之一,而藻细胞对Fe和P的吸收量分别提高了1.5倍和1倍.这些研究结果为揭示导致赤潮常在光照良好天气后发生的根本原因提供了全新的认识.     

改进的光谱角制图沿照度方向分类法及其应用——以ETM数据为例

选取多光谱遥感数据（ETM）对新疆北山西段中坡山笔架山一带进行了遥感蚀变信息提取方法研究。根据光谱角制图信息增强方法的优缺点,通过对光谱照度的研究,提出了结合光谱角分类方法进行沿光谱照度方向距离分类的信息提取方法。实验表明,该方法应用于ETM数据,增强了目标信息,同时剔除掉因照度所产生的大量非目标信息,为优化信息提供了一种有效的方法。在地形比较平坦的研究区取得了很好的应用效果。     

SSBUV and NOAA-11 SBUV/2 Solar Variability Measurements

The Shuttle SBUV (SSBUV) and NOAA-11 SBUV/2 instruments measured solar spectral UV irradiance during the maximum and declining phase of solar cycle 22. The SSBUV data accurately represent the absolute solar UV irradiance between 200–405 nm, and also show the long-term variations during eight flights between October 1989 and January 1996. These data have been used to correct long-term sensitivity changes in the NOAA-11 SBUV/2 data, which provide a near-daily record of solar UV variations over the 170–400 nm region between December 1988 and October 1994. The NOAA-11 data demonstrate the evolution of short-term solar UV activity during solar cycle 22.