Interaction between the atmospheric and oceanic boundary layers

The two-layer system of an atmosphere over water bodies is reduced to a single-layer problem. Values of the interfacial quantities, such as the friction velocity, the surface velocity, the angles, and , between the surface shear stress and the geostrophic wind velocity and the surface wind velocity, respectively, and the surface roughness, all of which depend upon external parameters, such as the geostrophic wind and stratifications, are obtained. The geostrophic drag coefficient C _d, the geostrophic wind coefficient C _f, and the angles , and , of the turbulent flow at the sea-air interface are functions of a dimensionless number, mfG/kg, with S ₁ and S ₂ as two free stratification parameters. The surface roughness is uniquely determined from the geostrophic wind rather than from the wind profile in the boundary layer.Formerly Visiting Research Associate, Applied Physics Branch, Earth Observations Division, NASA-Manned Spacecraft Center, Houston, Texas.     

Global monsoons in the mid-Holocene and oceanic feedback

The response of the six major summer monsoon systems (the North American monsoon, the northern Africa monsoon, the Asia monsoon, the northern Australasian monsoon, the South America monsoon and the southern Africa monsoon) to mid-Holocene orbital forcing has been investigated using a coupled ocean–atmosphere general circulation model (FOAM), with the focus on the distinct roles of the direct insolation forcing and oceanic feedback. The simulation result is also found to compare well with the NCAR CSM. The direct effects of the change in insolation produce an enhancement of the Northern Hemisphere monsoons and a reduction of the Southern Hemisphere monsoons. Ocean feedbacks produce a further enhancement of the northern Africa monsoon and the North American monsoon. However, ocean feedbacks appear to weaken the Asia monsoon, although the overall effect (direct insolation forcing plus ocean feedback) remains a strengthened monsoon. The impact of ocean feedbacks on the South American and southern African monsoons is relatively small, and therefore these regions, especially the South America, experienced a reduced monsoon regime compared to present. However, there is a strong ocean feedback on the northern Australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region. A new synthesis is made for mid-Holocene paleoenvironmental records and is compared with the model simulations. Overall, model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations.     

Retrieval of atmospheric and oceanic parameters and the relevant numerical calculation

It is well known that retrieval of parameters is usually ill-posed and highly nonlinear, so parameter retrieval problems are very difficult. There are still many important theoretical issues under research, although great success has been achieved in data assimilation in meteorology and oceanography. This paper reviews the recent research on parameter retrieval, especially that of the authors. First, some concepts and issues of parameter retrieval are introduced and the state-of-the-art parameter retrieval technology in meteorology and oceanography is reviewed briefly, and then atmospheric and oceanic parameters are retrieved using the variational data assimilation method combined with the regularization techniques in four examples： retrieval of the vertical eddy diffusion coefficient; of the turbulivity of the atmospheric boundary layer; of wind from Doppler radar data, and of the physical process parameters. Model parameter retrieval with global and local observations is also introduced.     

Probabilistic simulations of the impact of increasing leaf-level atmospheric carbon dioxide on the global land surface

Using a climate model with a sophisticated land surface scheme, simulations were conducted to explore the impact of increases in leaf-level carbon dioxide (CO₂) on evaporation, temperature and other land surface quantities. Fifty-one realizations were run, for each of four Januarys and four Julys for CO₂ concentrations at leaf-level of 280, 375, 500, 650, 840 and 1,000 ppmv. Atmospheric CO₂ concentration was held constant at 375 ppmv in all experiments. Statistically significant decreases in evaporation and increases in temperature occur in specific regions as leaf-level CO₂ is increased from 280 to 375 ppmv. These same areas expand geographically, and the magnitude of the changes increase as leaf-level CO₂ is increased further suggesting that changes are caused by the increase in leaf-level CO₂ and are not internal model variability. As leaf-level CO₂ is increased further, larger areas of the continental surface are affected by increasing amounts and a statistically significant change in precipitation is seen. The increase in leaf-level CO₂ from 280 ppmv to 375 ppmv causes statistically significant changes in the evaporation over 12% of continental surfaces in July. This increases to 25% at 500 ppmv, 35% at 650 ppmv, 41% at 840 ppmv and 47% at 1,000 ppmv. This affects temperature and rainfall by similar amounts, generally in coincident regions. An analysis of these results over key regions shows that the probability density functions of the latent heat flux and temperature are affected non-uniformly. There is a shift in the latent heat flux probability density function to lower values, mainly through the reduction in the upper tail of the distribution. The temperature probability density function shifts to higher values, mainly through an increase in the upper tail of the distribution indicating that the impact is focussed on extremes. Given that there are a suite of well evaluated land surface models that include the biogeochemical effects of increasing CO₂ we suggest that the inclusion of such a model should be a recommended component of climate models used in future assessment reports by the Intergovernmental Panel on Climate Change.     

An Observational Analysis of the Oceanic and Atmospheric Structure of Global-Scale Multi-decadal Variability简

The aim of the present study was to identify multi-decadal variability （MDV） relative to the current centennial global warming trend in available observation data.The centennial global wanning trend was first identified in the global mean surface temperature （STgm） data.The MDV was identified based on three sets of climate variables,including sea surface temperature （SST）,ocean temperature from the surface to 700 m,and the NCEP and ERA40 reanalysis datasets,respectively.All variables were detrended and low-pass filtered.Through three independent EOF analyses of the filtered variables,all results consistently showed two dominant modes,with their respective temporal variability resembling the Pacific Decadal Oscillation/Inter-decadal Pacific Oscillation （PDO/IPO） and the Atlantic Multi-decadal Oscillation （AMO）.The spatial structure of the PDO-like oscillation is characterized by an ENSO-like structure and hemispheric symmetric features.The structure associated with the AMO-like oscillation exhibits hemispheric asymmetric features with anomalous warm air over Eurasia and warm SST in the Atlantic and Pacific basin north of 10°S,and cold SST over the southern oceans.The Pacific and Atlantic MDV in upper-ocean temperature suggest that they are mutually linked.We also found that the PDO-like and AMO-like oscillations are almost equally important in global-scale MDV by EOF analyses.In the period 1975-2005,the evolution of the two oscillations has given rise to strong temperature trends and has contributed almost half of the STgm warming.Hereon,in the next decade,the two oscillations are expected to slow down the global warming trends.     

The impact of atmospheric and oceanic heat transports on the sea-ice-albedo instability during the Neoproterozoic

In order to simulate the climatic conditions of the Neoproterozoic, we have conducted a series of simulations with a coupled ocean–atmosphere model of intermediate complexity, CLIMBER-2, using a reduced solar constant of 6% and varied CO₂ concentrations. We have also tested the impact of the breakup of the supercontinent Rodinia that has been hypothesized to play an important role in the initiation of an ice-covered Earth. Our results show that for the critical values of 89 and 149 ppm of atmospheric CO₂, a snowball Earth occurs in the supercontinent case and in the dislocated configuration, respectively. The study of the sensitivity of the meridional oceanic energy transport to reductions in CO₂ concentration and to the dislocation of the supercontinent demonstrates that dynamics ocean processes can modulate the CO₂ threshold value, below which a snowball solution is found, but cannot prevent it. The collapse of the overturning cells and of the oceanic heat transport is mainly due to the reduced zonal temperature gradient once the sea-ice line reaches the 30° latitudinal band but also to the freshening of the tropical ocean by sea-ice melt. In term of feedbacks, the meridional atmospheric heat transport via the Hadley circulation plays the major role, all along the CO₂ decrease, by increasing the energy brought in the front of the sea-ice margin but does not appear enough efficient to prevent the onset of the sea-ice-albedo instability in the case of the continental configurations tested in this contribution.     

Measuring correlations between atmospheric oxygen and carbon dioxide mole fractions: A preliminary study in urban air

On 25 and 26 October 1986 the air in Cambridge, Massachusetts was monitored for O₂ and CO₂ mole fraction. O₂ concentrations were detected from changes in the relative refractivity of dried air between two lines of ¹⁹⁸Hg at 2537.269 and 4359.562 Å using dual-wavelength interferometry. Changes in oxygen mole fraction were resolved with two-minute time resolution to a precision of ±2.0 ppm. Changes in O₂ were shown to be strongly anticorrelated with changes in CO₂ as expected for combustion processes. The demonstrated instrumental capabilities are appropriate for measuring changes in O₂ mole fraction in background air which could be of importance to a broad range of biogeochemical studies.     

Low-frequency variability of the arctic climate: the role of oceanic and atmospheric heat transport variations

Changes in meridional heat transports, carried either by the atmosphere (HTRA) or by the ocean (HTRO), have been proposed to explain the decadal to multidecadal climate variations in the Arctic. On the other hand, model simulations indicate that, at high northern latitudes, variations in HTRA and HTRO are strongly coupled and may even compensate each other. A multi-century control integration with the Max Planck Institute global atmosphere-ocean model is analyzed to investigate the relative role of the HTRO and HTRA variations in shaping the Arctic climate and the consequences of their possible compensation. In the simulation, ocean heat transport anomalies modulate sea ice cover and surface heat fluxes mainly in the Barents Sea/Kara Sea region and the atmosphere responds with a modified pressure field. In response to positive HTRO anomalies there are negative HTRA anomalies associated with an export of relatively warm air southward to Western Siberia and a reduced inflow of heat over Alaska and northern Canada. While the compensation mechanism is prominent in this model, its dominating role is not constant over long time scales. The presence or absence of the compensation is determined mainly by the atmospheric circulation in the Pacific sector of the Arctic where the two leading large-scale atmospheric circulation patterns determine the lateral fluxes with varying contributions. The degree of compensation also determines the heat available to modulate the large-scale Arctic climate. The combined effect of atmospheric and oceanic contributions has to be considered to explain decadal-scale warming or cooling trends.     

Credited forest carbon sinks: how the cost reduction is allocated among countries and sectors

Forest carbon sinks have been included in the Kyoto Protocol as one of the mechanisms for mitigating climate change. Consequently, credited sinks decrease the need to reduce emissions.We analyse in detail both the economywide and the sectoral effects of inclusion of carbon sinks as agreed upon in Bonn and Marrakesh for the first commitment period of 2008–2012. The focus of our analysis is the special treatment for Canada and Japan that allows them larger sinks. The analysis is performed with the multi-region computable general equilibrium (CGE) model GTAP-E.

New Zealand benefits most from the inclusion of sinks as it gains large carbon sinks from afforestation. Also in Sweden, Canada and Japan the costs of achieving the emission target are considerably reduced. Of these countries, only Canada has high costs without sinks. Thus credited sinks partly reduce the difference in economic burden of achieving the Kyoto target among countries. Even though larger sinks clearly benefit Canada and Japan, their effect on other countries, either on the economywide or on the sectoral level, remains marginal. Allowing larger sinks is, indeed, of relatively minor importance for the world economy and emission reduction, compared to the US withdrawal from the Kyoto Protocol.     

Rural-urban connectivity and agricultural land management across the Global South

Research on how urbanization affects rural agriculture has typically focused on loss of farmland due to urban expansion. However, more distal pathways that could link urbanization to rural agriculture, including enhanced connectivity through rural-urban migration and market access, remain poorly understood. Here, we assess whether greater rural-urban connectivity is associated with changes in agricultural land management across the Global South. Such associations are complex, and thus difficult to measure at this scale. We therefore take a two-step approach to investigate these relationships. First, using a multivariate clustering approach, we define a series of rural-urban connectivity typologies from existing spatial data on land use, demographics, rural market access, and rural population change (as a proxy for outmigration). We examine the variation in key agricultural outcome variables (mean cereal crop yields, % of attainable yields met, and cropping frequency) within the typologies, which shows that greater overall connectivity (market access and population change) is associated with higher cereal yields, yield attainment, and cropping frequency. Second, building on these clustering results, we develop hypotheses about the relationship between rural-urban connectivity and agricultural land use intensity. We then use propensity score matching to test these hypotheses by comparing locations with similar sociodemographic and land use characteristics. When controlling for gross domestic product (GDP) per capita, agricultural land, and population density, rural locations with relatively high market access, negative population change, and greater built-up area have significantly higher mean nitrogen application rates, irrigated areas, and cereal yields across the Global South. Results vary by region, but greater rural-urban connectivity and urban extents are generally associated with higher overall agricultural inputs and yields, particularly in Asia. However, we find little support for a relationship between connectivity and either % attainable yields met or field size. Our findings stress the need to better understand the mechanisms that link urbanization processes and agricultural management at different spatiotemporal scales.     

Credited forest carbon sinks: how the cost reduction is allocated among countries and sectors

Forest carbon sinks have been included in the Kyoto Protocol as one of the mechanisms for mitigating climate change. Consequently, credited sinks decrease the need to reduce emissions. We analyse in detail both the economywide and the sectoral effects of inclusion of carbon sinks as agreed upon in Bonn and Marrakesh for the first commitment period of 2008–2012. The focus of our analysis is the special treatment for Canada and Japan that allows them larger sinks. The analysis is performed with the multi-region computable general equilibrium (CGE) model GTAP-E.New Zealand benefits most from the inclusion of sinks as it gains large carbon sinks from afforestation. Also in Sweden, Canada and Japan the costs of achieving the emission target are considerably reduced. Of these countries, only Canada has high costs without sinks. Thus credited sinks partly reduce the difference in economic burden of achieving the Kyoto target among countries. Even though larger sinks clearly benefit Canada and Japan, their effect on other countries, either on the economywide or on the sectoral level, remains marginal. Allowing larger sinks is, indeed, of relatively minor importance for the world economy and emission reduction, compared to the US withdrawal from the Kyoto Protocol.     

A study on the variability of atmospheric and oceanic processes over the Arabian Sea during contrasting monsoons

Summary The atmospheric and oceanic conditions associated with the southwest monsoon during the contrasting monsoon years of 2002 and 2003 over the Arabian Sea have been analyzed in the present study. Early onset of southwesterlies and reduced net heat gain due to low solar radiation were responsible for low sea-surface temperatures (SSTs) over the Arabian Sea during 2002 pre-monsoon (particularly in May). Conversely, light winds and an increased net heat gain set up the pre-monsoon warming in 2003. The development and intensification of deep convection over a large area of the Arabian Sea prior to the onset of the monsoon was observed during 2003, but was absent in 2002. Weak cross equatorial flow and a weak low level jet over the Arabian Sea reduced moisture transport towards the Indian subcontinent in July 2002. This scenario helped to contribute to a prolonged break in monsoon conditions during July. However, no such break in conditions occurred during July 2003. In 2002, the summer monsoon cooling of the Arabian Sea occurred well before July, whereas in 2003 cooling occurred during July. Estimates of wind driven Ekman (horizontal) and vertical transports showed maximum values in the month of June (July) in 2002 (2003). These estimates clearly show the importance of horizontal and vertical advection in the summer cooling of the Arabian Sea. During the southwest monsoon period, the Arabian Sea was warmer in 2003 than in 2002. Late onset of the southwesterlies in June, late cooling of the Arabian Sea in July, and downwelling Rossby wave propagation were responsible for the warm SSTs in 2003. Weak wind stress curl in July dampened the westward propagating sea surface height anomaly signals (Rossby waves) before they reached the western Arabian Sea in 2002, whereas, in 2003 strong wind stress curl enhanced Rossby wave propagation. During the summer monsoon period, subsurface temperatures in the south central Arabian Sea were warmer in 2003 than in 2002, particularly in July and August. Strong Ekman convergence, solar penetration, and downwelling (downward velocities) are responsible for the enhanced subsurface warming in 2003.     

Large-Scale features of the indian summer monsoon rainfall and their association with some oceanic and atmospheric variables

The summer monsoon rainfall totals for 31 meteorological subdivisions of India for the years 1901-1980 are analysed. The analysis reveals that four leading eigenvectors (EVs) are significant and account for 65 % of the total variance.The spatial pattern of the first EV exhibits in phase fluctuations over almost the whole India. The large coefficients of this vector can be considered as representative of the conditions of large-scale flood and drought over the country. The second pattern reveals the fluctuations mostly over the North Indian region (north of 20o latitude) probably in association with the Western Disturbances. The third pattern indicates fluctuations over the North-West and the North-East India in opposite phase and the fourth pattern exhibits the characteristic features of fluctuations associated with ‘break’. The spectral analysis of the coefficients of these EVs revealed quasi-periodicities of 2-5 years.On the basis of examination of the elements of these EVs the country has been divided into seven homogeneous regions. Rainfall indices of these regions and of the four EVs have been examined for seek-ing for association with some oceanic and atmospheric variables. The association is significant for the coefficients of the first EV and for the rainfall indices of central and South India. Among all the variables examined, Darwin pressure tendencies have the highest association and appear to be of special significance in prediction of the monsoon rainfall.     

中国东部夏季不同雨带类型的海洋和环流特征差异

利用1951-2009年NCEP/NCAR再分析资料、UKMO HADISST1全球月海表温度及中国东部地区120站的月降水量资料,首先定义出能够客观表征中国东部夏季3种雨带类型的指数,然后分析了3种雨带分布类型海洋和大气环流特征的主要差异,并进一步分析了前期海洋背景的差异特征对夏季东亚环流关键系统的预测蕴示.结果表明:(1)3种雨带类型对应的前期冬季海洋信号比当年夏季强,其差异主要表现在:多雨带出现在北方地区的Ⅰ型对应的是北太平洋海温呈显著的正距平、暖池及东澳暖流为负距平、南太平洋西风漂流区为正距平;多雨带出现在黄淮地区的Ⅱ型对应的海温分布则与Ⅰ型完全相反;多雨带出现在长江及其以南地区的Ⅲ型对应的海温分布在北太平洋海域与Ⅰ型基本一致;(2)3种雨带类型对应的环流及水汽输送特征的差异主要表现在:Ⅲ型与Ⅰ型具有几乎完全相反的环流及水汽输送特征,当出现Ⅲ型时,东亚中高纬度有强盛的阻塞形势发展和维持,中高纬度的经向环流异常加强,同时西太平洋副热带高压偏强,位置偏西、偏南,该地区呈反气旋性距平环流,西太平洋副热带纬向水汽输送加强,而出现Ⅰ型时则相反;Ⅱ型与Ⅰ型的环流及水汽输送特征更接近,两者的主要差异是:当出现Ⅱ型时,西太平洋副热带地区呈反气旋性距平环流,而出现Ⅰ型时该地区呈气旋性距平环流;(3)前期冬季赤道中东太平洋海温和南太平洋西风漂流区的海温异常变化可以作为夏季西太平洋副热带高压预报的重要前兆信号.