Florida current: low-frequency variability as observed with moored current meters during april 1982 to june 1983

A 1-year time series of volume transport through the Florida Straits near 27 degrees N was derived from an array of five subsurface current meter moorings. The transport estimates, determined on the basis of constant shear extrapolation of the subsurface velocities to the surface, are in good agreement with transports derived from submarine cable and Pegasus measurements. The annual transport cycle in 1982-1983 is complicated by large-amplitude fluctuations on time scales of 1 to 3 weeks, but it does exhibit a transport maximum in summer and a minimum in fall-winter, consistent with historical results and of similar magnitude. The energy density spectrum of transports is continuous with a slope of about -1.5 and does not show a gap between the periods of weeks and seasonal. Evidence was found for atmospheric forcing of transport fluctuations, with highest coherence between transport and the local meridional wind stress at periods of 10 and 15 days during the summer and 5 and 40 days during the winter.     

植被年际变化对蒸散发影响的模拟研究

利用通用陆面模式(CLM3.0)及其植被动力学模式(DGVM)研究植被覆盖度(FC)和叶面积指数(LAI)的年际变化对全球蒸散发的影响。设计两套实验方案,其植被的FC和LAI的气候态相同,但一套实验中植被的FC和LAI有年际变化,而对照实验中则没有。结果表明:(1)在草、灌木、树占优势的地区植被FC年际变化依次减小;LAI年际变化较大的地区集中在草和灌木覆盖的地区,在落叶林地区,春秋两季植被LAI的年际变化也较大。(2)全球树占优势的大部分地区,植被的年际变化使得年平均蒸散发和地表蒸发增加、冠层蒸发和蒸腾减少;而在灌木和草覆盖区,变化则大致相反。(3)低纬度地区蒸散发季节循环变化比较明显,而北半球中纬度地区,蒸散发变化明显区随着纬度增加而在时间上向后推延。(4)FC和LAI年际变化较大时,蒸散发及地表蒸发降低,而蒸腾增加;这些差异随FC和LAI年际变化的增加而增加。单点分析进一步表明植被年际变化不仅改变蒸散发的多年平均值,同时改变其分量间的相对比例。     

Small interannual variability of global atmospheric hydroxyl

The oxidizing capacity of the global atmosphere is largely determined by hydroxyl (OH) radicals and is diagnosed by analyzing methyl chloroform (CH(3)CCl(3)) measurements. Previously, large year-to-year changes in global mean OH concentrations have been inferred from such measurements, suggesting that the atmospheric oxidizing capacity is sensitive to perturbations by widespread air pollution and natural influences. We show how the interannual variability in OH has been more precisely estimated from CH(3)CCl(3) measurements since 1998, when atmospheric gradients of CH(3)CCl(3) had diminished as a result of the Montreal Protocol. We infer a small interannual OH variability as a result, indicating that global OH is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases oxidized primarily by OH, as well as global photochemical model calculations.     

Florida current volume transports from voltage measurements

The volume transport of the Florida Current is determined from the motionally induced voltage difference between Florida and Grand Bahama Island. Simultaneous measurements of potential differences and of volume transport by velocity profiling have a correlation of 0.97. The calibration factor is 25+/- 0.7 sverdrups per volt, and the root-mean-square discrepancy is 0.7 sverdrup. The induced voltage is about one-half the open-circuit value, implying that the conductance of the sediments and lithosphere is about equal to that of the water column.     

Reduced interannual rainfall variability in East Africa during the last ice age

Interannual rainfall variations in equatorial East Africa are tightly linked to the El Ni?o Southern Oscillation (ENSO), with more rain and flooding during El Ni?o and droughts in La Ni?a years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall.     

Volume and heat transports of the Florida current: april 1982 through august 1983

Absolute velocity and temperature profiles are used to estimate the volume transport through the Straits of Florida and, in combination with historical midbasin data, to estimate the total meridional heat flux through a section at 27 degrees N. The mean annual volume transport of the Florida Current from April 1982 through August 1983 is 30.5 (+/- 1)x 10(6) cubic meters per second. The net northward heat flux through the 27 degrees N section is 1.2 (+/- 0.1)x 10(15) watts. The volume transport is characterized by high values in the late spring and early summer and low values in the late fall and early winter. There is a similar cycle in total heat flux.     

European seasonal and annual temperature variability, trends, and extremes since 1500

Multiproxy reconstructions of monthly and seasonal surface temperature fields for Europe back to 1500 show that the late 20th- and early 21st-century European climate is very likely (>95% confidence level) warmer than that of any time during the past 500 years. This agrees with findings for the entire Northern Hemisphere. European winter average temperatures during the period 1500 to 1900 were reduced by approximately 0.5 degrees C (0.25 degrees C for annual mean temperatures) compared to the 20th century. Summer temperatures did not experience systematic century-scale cooling relative to present conditions. The coldest European winter was 1708/1709; 2003 was by far the hottest summer.     

Sea level variation as an indicator of Florida current volume transport: comparisons with direct measurements

Sea level measurements from tide gauges at Miami, Florida, and Cat Cay, Bahamas, and bottom pressure measurements from a water depth of 50 meters off Jupiter, Florida, and a water depth of 10 meters off Memory Rock, Bahamas, were correlated with 81 concurrent direct volume transport observations in the Straits of Florida. Daily-averaged sea level from either gauge on the Bahamian side of the Straits was poorly correlated with transport. Bottom pressure off Jupiter had a linear coefficient of determination ofr(2) = 0.93, and Miami sea level, when adjusted for weather effects, had r(2) = 0.74; the standard errors of estimating transports were +/- 1.2 x 10(6) and +/- 1.9 x 10(6) cubic meters per second, respectively. A linear multivariate regression, which combined bottom pressure, weather, and the submarine cable observations between Jupiter and the Bahamas, had r(2) = 0.94 with a standard error of estimating transport of +/- 1.1 x 10(6) cubic meters per second. These results suggest that a combination of easily obtained observations is sufficient to adequatelv monitor the daily volume transport fluctuations of the Florida Current.     

不同灌溉方式对设施菜地N2O排放的影响及其年际差异

通过田间原位试验,利用自动静态箱-气相色谱法对设施黄瓜季土壤N_2O排放进行了连续两年的观测,探讨了不同灌溉方式(传统漫灌和滴灌)对N_2O排放的影响及其年际差异,以期为设施菜地N_2O减排提供数据支撑和理论基础。试验设置3个处理,分别为对照处理(CK)、漫灌施肥处理(FP)、滴灌施肥处理(FPD)。CK处理不施氮肥,FP、FPD处理氮肥施用量为有机肥500 kg N·hm~(-2)、化肥700 kg N·hm~(-2),其中化肥根据作物养分需求多次施入。研究结果表明:设施菜地N_2O排放峰主要集中于施肥和灌溉后,基肥持续7 d左右,追肥N_2O排放峰持续3~5 d。土壤温度、水分和气温等因子都能显著影响N_2O排放通量的变化,但不同年际之间对N_2O排放的影响不同,2015年N_2O排放通量的变化主要受土壤温度和气温影响,而2016年主要受土壤湿度和温度影响;改变灌溉方式,对土壤温湿度变化没有产生显著的影响;相同氮肥施用量下,滴灌相比常规漫灌在提高作物产量的同时,能减少N_2O排放总量29.4%~35.1%,并且没有显著年际差异;滴灌相比常规漫灌能减少N_2O排放强度(即单位经济产量N_2O排放量)34.5%~37.5%、排放系数47.2%~47.7%,两年的观测没有显著的年际差异。可见,滴灌相比漫灌在提高蔬菜产量的同时,能显著减少N_2O排放,而且年际之间没有显著差异,是设施菜地值得推荐的一种减排技术,并可为N_2O长期减排效果的估算提供参考。     

Temporal variability of the antarctic circumpolar current observed from satellite altimetry

Sea level measurements by the Seasat altimeter were used to study the temporal variability of the Antarctic Circumpolar Current between July and October 1978. Large-scale zonal coherence in the cross-stream sea level difference was observed, indicating a general increase in the surface geostrophic velocity of the current around the Southern Ocean. The result demonstrates the power of satellite altimetry to monitor the variability of large-scale ocean currents.     

Coal mine explosions: seasonal trends

An analysis of disaster reports on coal mine explosions indicates that gas explosions are randomly distributed throughout the year, whereas dust explosions (which may or may not be triggered by a gas explosion) occur with greater frequency during the dry fall and winter months. The lack of adequate moisture during cold weather tends to increase the rate and severity of the dust explosions.     

Seeding cumulus in Florida: new 1970 results

In the Florida single cloud experiments, the main result of the statistical analyses is that the dynamic seeding effect on rainfall is large, positive, and significant. From all the 1968 and 1970 data together, the seeding effect is estimated to be larger than a factor of 3; that is, the seeded clouds rained more than three times as much as the controls after the seeding run. On fair days, defined objectively by percentage of area covered by showers, the seeding effect is shown to be larger than the overall average, but it may be negative on rainy days. Rainy days in the tropics are about 10 percent of the days with rain, but they produce about half the total rainfall. The applicability of our single cloud results to other areas is not established but seems hopeful for many tropical and subtropical regions. It can be assessed by cloud population studies together with our numerical model (25). Guidance for the next steps toward practical rainfall enhancement and toward the understanding and modification of cloud systems in storms may be provided by our study of merger clouds. Mergers are shown often to produce more than an order of magnitude more rain than isolated clouds on the same day, probably owing to dynamic invigoration of the merged cloud circulations. Results of our first small attempt toward inducing and documenting mergers in a multiple cloud seeding experiment appear promising. Although far from statistically conclusive, they have opened a new frontier in the science and technology of dynamic cloud modification. It is also hoped that the multiple cumulus seeding experiments will help to clarify the formation of "cloud clusters" and their role in large-scale circulations, thus contributing to the focal subject of the Global Atmospheric Research Program in the tropics.     

Acid precipitation and sulfate deposition in Florida

The acidity of rainfall in Florida has increased markedly in the past 25 years, and the average sulfate and nitrate concentrations have increased by factors of 1.6 and 4.5, respectively, over the period. Annual average pH values below 4.7 now occur over the northern three quarters of the state. Summer rainfall has average pH values 0.2 to 0.3 unit lower than winter rainfall, and sulfate concentrations at most sites are higher in summer. The annual deposition of H(+) (about 300 to 500 equivalents per hectare) in northern Florida is a third to a half of the deposition in the heavily impacted northeastern United States; comparable figures for excess sulfate (derived from sulfur dioxide) are 7 to 11 kilograms of sulfur per hectare or 50 to 90 percent of the sulfate deposition rates at Hubbard Brook, New Hampshire.     

Sex ratio of sea turtles: seasonal changes

Sex ratios of hatchling loggerhead turtles Caretta caretta taken from South Carolina and Georgia ranged from no females in nests laid in late May to 80 percent females in those laid in early July; the sex ratio decreased to 10 percent females in nests laid in early August. These seasonal changes are consistent with the role of temperature in directing sexual differentiation in various reptiles. The data have implications for understanding the demography of sea turtles and for their conservation.     

Cloud seeding experiments: lack of bias in Florida series

There has been concern about the possibility of selection bias in cloud seeding experiments. Covariates and experimental design have been used to obtain an estimate of this bias. The results indicate that there was no selection bias in the Caribbean and Florida series of cloud seeding experiments.