Methane Emission Reduction: An Application of FUND

Methane is, after carbon dioxide, the most important anthropogenic greenhouse gas. Governments plan to abate methane emissions. A crude set of estimates of reduction costs is included in FUND, an integratedassessment model of climate change. In a cost-benefit analysis, methane emission reduction is found to be instrumental in controlling the optimal rate of climate change. In a cost-effectiveness analysis, methane emission reduction largely replaces carbon dioxide emission reduction. Methane emission reduction reinforces the case for international cooperation in climate policy, but complicates the efficient allocation of emission reduction efforts. Methane emission reduction at the short run does not help to achieve the ultimate objective of the Framework Convention on Climate Change.     

Estimating Buoyancy Heat Flux Using the Surface Renewal Technique over Four Amazonian Forest Sites in Brazil

The surface renewal (SR) method was applied for the first time to measurements of air temperature over four Amazonian forest sites and different seasons in order to obtain estimates of buoyancy heat flux. The required calibration of this method against eddy covariance resulted in a value for a specific parameter that is close to the range reported in other studies, contributing to the generalization of the SR method to different kinds of canopies. The comparison with fluxes obtained using the eddy covariance technique revealed a good match between the two methods for different sites, heights and seasons. Sites with high levels of non-stationarity in the signals of temperature and wind speed presented higher scatter in the regression with fluxes from eddy covariance. For a particular site with previously reported influence of low-frequency motions, the regression was only satisfactory, i.e., slope parameter close to unity and small offset, when oscillations with periods longer than $\approx $ ≈ 13 min were filtered out. The SR method has a great potential due to the simplicity of the instrumentation required. However, care should be taken when measuring under the influence of mesoscale motions, which can lead to high levels of non-stationarity, compromising the fundamental concepts of the SR theory.     

IMPACT OF LATENT HEAT FLUX ON INDIAN SUMMER MONSOON DURING EL NI(N)O/LA NI(N)A YEARS

El Ni(n)o or La Ni(n)a manifest in December over the Pacific and will serve as an index for the forecasting of subsequent Indian summer monsoon,which occurs from June to mid-September.In the present article,an attempt is made to study the variation of latent heat flux (LHF) over the north Indian Ocean during strong El Ni(n)o and strong La Ni(n)a and relate it with Indian monsoon rainfall.During strong El Ni(n)o the LHF intensity is higher and associated with higher wind speed and lower cloud amount.During E1 Ni(n)o all India rainfall is having an inverse relation with LHF.Seasonal rainfall is higher in YY+1 (subsequent year) than YY (year of occurrence).However there is a lag in rainfall during El Ni(n)o YY+1 from June to July when compared with the monthly rainfall.     

Stratosphere-troposphere Dynamical Coupling over Boreal Extratropics during the Sudden Stratospheric Warming in the Arctic in January–February 2017

The dynamic coupling between the stratospheric and tropospheric processes is studied for the sudden stratospheric warming registered in January-February 2017. Also, the effects of these processes on the tropospheric circulation and weather conditions in the middle and high latitudes via the reflection of wave activity from the stratosphere are investigated.     

Boundary-layer depth and entrainment zone characterization with a boundary-layer profiler

A technique for determining the height of the convective atmospheric boundary layer (CBL) with a 915 MHz boundary-layer profiler is discussed. The results are compared with CBL heights determined from radiosonde measurements. The profiler provides continuous CBL height measurements with very good time resolution (30 minutes or less), allowing for detailed understanding of the growth and fluctuations of the CBL. In addition, the profiler provides information about the degree of definition of the CBL top and the thickness of the entrainment zone. The measurements discussed were taken during the Rural Oxidants in the Southern Environment II (ROSE II) experiment.     

The role of the subtropical jet stream during heat wave events over north-central Greece

Summary The role of the subtropical jet stream (SJ) in the occurrence of heat waves in South Balkans and Greece is sought here. For this purpose ECMWF grid-point data is examined, concerning the Balkan heat wave of 5–9 July 1988, that cost human lifes, at least in Greece. For the city of Thessaloniki, Greece, a temperature budget is presented, as a function of time. It turns out that the most important heating mechanism is the adiabatic heating. Horizontal mass convergence at the maximum wind level (200 hPa) causes descent and adiabatic heating. The convergence occurs in association with the Hadley Cell, as well as with the right exit quadrant of an anticyclonically curved subtropical jet streak. As air parcels that exit the above jet streak slow down and turn anticyclonically, a strong ageostrophic wind current is established towards and to the right of the flow direction. This ageostrophic current converges above the northeastern Balkans. Downward ageostrophic motion emerges from the above area of horizontal convergence and heads towards the SSW, affecting the Balkans. From the above case study, it is concluded that intense heat waves are favoured in the South Balkans and Greece when the SJ is anticyclonically curved to the north of the Balkans and a jet streak is situated to the north west of the Balkans.     

Radiative Processes in the Stable Boundary Layer: Part I. Radiative Aspects

The structure of the radiatively dominated stable boundary layer is analysed using idealized calculations at high vertical and spectral resolution. The temperature profile of a nocturnal radiative boundary layer, developing after the evening transition, is found to be well described in terms of radiative cooling to the surface, although radiative exchanges within the atmosphere become increasingly important with time. The treatment of non-black surfaces is discussed in some detail and it is shown that the effect of reducing the surface emissivity is to decrease rather than to increase the radiative cooling rate in the surface layer. It is also argued that an accurate assessment of the impact of non-black surfaces requires careful attention to the spectral and directional characteristics of the surface emissivity. A polar nocturnal boundary layer, developing above snow-covered ground, is simulated and found to reach a slowly evolving state characterized by a strong radiative divergence near the surface that is comparable to observed values. Radiative boundary layers are characterized by large temperature gradients near the surface. An erratum to this article can be found at     

Identifying Key Sources of Uncertainty in Climate Change Projections

What sources of uncertainty shouldbe included in climate change projections and whatgains can be made if specific sources of uncertaintyare reduced through improved research?DIALOGUE, anintegrated assessment model, has been used to answerthese questions. Central in the approach of DIALOGUEis the concept of parallel modeling, i.e., for eachstep in the chain from emissions to climate change anumber of equivalent models areimplemented. The followingconclusions are drawn:The key source of uncertainty in global temperatureprojections appears to be the uncertainty inradiative forcing models. Within this group ofmodels uncertainty within aerosol forcing models isabout equal to the total forcing of greenhouse gasmodels. In the latter group CO₂ is dominant.The least important source of uncertainty appears tobe the gas cycle models. Within this group of modelsthe role of carbon cycle models is dominant.Uncertainty in global temperature projections hasnot been treated consistently in the literature.First, uncertainty should be calculated as a productof all uncertainty sources. Second, aparticular choice of a base year for global warmingcalculations influences the ranking of uncertainty.Because of this, a comparison of ranking resultsacross different studies is hampered. We argue that`pre-Industrial' is the best choice for studies onuncertainty.There is a linear relationship between maximumuncertainty in the year 2100 and cumulativeemissions of CO₂ over the period 1990–2100:higher emissions lead to more uncertainty.