Publications

The state of knowledge and outstanding issues with respect to the global mean energy budget of planet Earth are described, along with the ability to track changes over time. Best estimates of the main energy components involved in radiative transfer and energy flows through the climate system do not satisfy physical constraints for conservation of energy without adjustments. The main issues relate to the downwelling longwave (LW) radiation and the hydrological cycle, and thus the surface evaporative cooling. It is argued that the discrepancy is 18% of the surface latent energy flux, but only 4% of the downwelling LW flux and, for various reasons, it is most likely that the latter is astray in some calculations, including many models, although there is also scope for precipitation estimates to be revised. Beginning in 2000, the top-of-atmosphere radiation measurements provide stable estimates of the net global radiative imbalance changes over a decade, but after 2004 there is “missing energy” as the observing system of the changes in ocean heat content, melting of land ice, and so on is unable to account for where it has gone. Based upon a number of climate model experiments for the twenty-first century where there are stases in global surface temperature and upper ocean heat content in spite of an identifiable global energy imbalance, we infer that the main sink of the missing energy is likely the deep ocean below 275 m depth.

Planned adaptation to climate change requires information about what is happening and why. While a long-term trend is for global warming, short-term periods of cooling can occur and have physical causes associated with natural variability. However, such natural variability means that energy is rearranged or changed within the climate system, and should be traceable. An assessment is given of our ability to track changes in reservoirs and flows of energy within the climate system. Arguments are given that developing the ability to do this is important, as it affects interpretations of global and especially regional climate change, and prospects for the future.

Global warming first became evident beyond the bounds of natural variability in the 1970s, but increases in global mean surface temperatures have stalled in the 2000s. Increases in atmospheric greenhouse gases, notably carbon dioxide, create an energy imbalance at the top‐of‐atmosphere ( TOA ) even as the planet warms to adjust to this imbalance, which is estimated to be 0.5–1 W m −2 over the 2000s. Annual global fluctuations in TOA energy of up to 0.2 W m −2 occur from natural variations in clouds, aerosols, and changes in the Sun. At times of major volcanic eruptions the effects can be much larger. Yet global mean surface temperatures fluctuate much more than these can account for. An energy imbalance is manifested not just as surface atmospheric or ground warming but also as melting sea and land ice, and heating of the oceans. More than 90% of the heat goes into the oceans and, with melting land ice, causes sea level to rise. For the past decade, more than 30% of the heat has apparently penetrated below 700 m depth that is traceable to changes in surface winds mainly over the Pacific in association with a switch to a negative phase of the Pacific Decadal Oscillation ( PDO ) in 1999. Surface warming was much more in evidence during the 1976–1998 positive phase of the PDO , suggesting that natural decadal variability modulates the rate of change of global surface temperatures while sea‐level rise is more relentless. Global warming has not stopped; it is merely manifested in different ways.

No abstract is provided for this article.

The Eliassen-Palm (E-P) flux, applied to zonal men flows, is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow. For time mean flows, a localized E-P flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the South Pacific during the Southern Hemisphere winter of 1979. In contrast to previous studies that have focused on the mean quasi-geostrophic potential vorticity equation, the focus here is on the mean momentum equations. Eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance, are gathered together allowing the residual circulation and the effects of the eddies to be determined. The time-mean equations of motion are thus transformed to consist of mean terms, the residual circulation and the divergence of a localized E-P flux vector. The latter is a measure of the eddy forcing of the mean flow, and the east-west component is shown to be related to the flux of wave activity. For the zonal mean case it is identical to the E-P flux. The local E-P flux is closely related to, but differs from, the E-vector of Hoskins et al. and Plumb's radiative wave activity flux, but has several advantages over both. For the blocking episode, defined as 20 July-31 August 1979, transient eddies were steered around the location of the blocking anticyclones following the two branches of the split westerly jet. However, the transient eddies in each branch differed in character, both from each other and from those in the main Southern Hemisphere storm track that extends across the southern Indian Ocean near 50°S. In the latter, the high frequency synoptic-scale baroclinic eddies are barotropically damped. The eddies have similar character to the south of the block but consist mainly of zonal wavenumbers 3 and 4 with periods shorter than a week. In contrast, the transient eddies in the subtropical branch of the jet are higher wavenumber (mostly waves 5 and 6) with periods longer than a week and, although primarily baroclinic, they are also maintained by barotropic processes. Most transient wave energy propagates eastward and wave packets can be followed around the entire hemisphere, mostly following the split westerly jet, with a period of about six days. The local E-P flux divergence is divided into barotropic and baroclinic components. The former is coherent in the vertical but strongest at 300 mb near the tropopause. The transient eddies barotropically accelerate the westerlies in the main storm track and branch south of the block, and this is partially balanced by the baroclinic component. Thus a large part of the momentum balance is between transient eddy momentum convergence and the Coriolis torque arising from the poleward heat transport induced Ferrel cell, in combination with Surface friction. Where the main westerly jet splits as part of the blocking flow configuration, both the barotropic and baroclinic local E-P flux components are acting to decelerate the westerlies and thus the transient eddies are helping to maintain the blocking episode. The main differences between the storm track and blocking regions arise in the barotropic component of the local E-P flux. It appears that the configuration of the split westerly jet acts to systematically deform the transient eddies in such a way that they feed back to help maintain the split structure.

The flow of energy through the climate system is described along with its perturbations arising from human-induced climate change. The role of the atmosphere, oceans, land, and ice components of the climate system are detailed along with the hydrological cycle and interactions that give rise to large variability, such as the El Niño phenomenon. The mass and specific heat of the main components play a major role in storing and moving heat and energy around. The main cause of climate change is the changes in composition of the atmosphere and the enhanced greenhouse effect from increasing carbon dioxide and other greenhouse gases, offset somewhat by pollution. This produces an Earth Energy Imbalance, and the extra heat has profound influences, including increasing the global mean surface temperature.

Diurnal (or sub-daily) variations are large in many surface and atmospheric fields such as solar radiation, surface latent and sensible heat fluxes, surface temperature and winds, atmospheric convection, and precipitation. These diurnal variations are especially important in air-land and air-sea interactions, which are highly non-linear and thus can not be resolved using daily mean values. Current regional and global climate models still have difficulties in simulating the diurnal variations correctly. Here we analyze the diurnal variations in surface air temperature and pressure, precipitation, and cloudiness simulated by the Community Climate System Model (CCSM), a state-of-art climate system model developed by a large number of scientists from the National Center for Atmospheric Research (NCAR) and partner institutions. The CCSM simulates well some aspects of diurnal variations such as the diurnal and semidiurnal pressure tides, and the diurnal cycle of temperature over land; but it has large biases in simulating diurnal cycles in cloud amount, moist convection, and precipitation. Diurnal variations over the oceans are too weak in the CCSM mainly because the surface ocean has no diurnal cycle in the model.

No abstract is provided for this article.

The evolution of the Southern Oscillation (SO) is examined in the time domain by computing lagged cross correlations between sea level pressures at Darwin and sea level or surface pressures at selected stations. Also, in the Northern Hemisphere, the historical and U.S. Navy sea level pressure analyses are used. All monthly time series are low-pass filtered to retain periodicities greater than 20 months in order to highlight the interannual fluctuations which are primarily associated with the SO. A detailed analysis of the post-1941 period results in plotted maps of the phase (lead or lag) and magnitude of the maximum cross correlations with Darwin, in a manner analogous to a broadband coherence and phase spectrum. The relationships within the SO are further examined, where possible, back to 1882 using time series of running decadal cross covariances. The dominant pattern reveals the two poles of the traditional standing oscillation or seesaw of the SO, with centers of opposite sign over Indonesia and the central South Pacific Ocean. But there are significant phase variations within each center and clear indications that changes over the South Pacific lead the opposite changes in the Indonesian pole by 1–2 seasons. Largest leads of three seasons begin near New Zealand but quickly spread over the subtropics of both hemispheres in the Pacific. Typically 1–3 seasons later, opposite anomalies begin over the Indian region and progress east and southeast into the western Pacific. Significant positive and negative lagged correlations occur only in the New Zealand area. For the post-1950 period, which is the basis for most recent analyses of El Niño–SO events, the SO was dominated by a three-six year quasi-periodicity which leads to ambiguity in interpreting phase relationships. The pattern of leads and lags is consistent with a progression of anomalies from southeast Australia across New Zealand and into the Pacific about two years later. The progression is not very regular, often occurring in discrete jumps. Moreover, it requires reinterpretation of the negative correlations as positive correlations that are half a period (π radians) out of phase. Eastward propagation is likely to be exaggerated by the implied cyclicity imposed by analyses in the frequency domain. Over the longer term (1882–1984) the ambiguity is lessened and the two poles are seen to be more distinct. Systematic leads are still apparent over the subtropics of the Pacific but the evidence for an eastward-propagating component extending from Australia across the southwest Pacific is not consistent throughout the record. The results show that caution must be exercised in interpreting the post-1950 period as representative of the long-term mean behavior. The importance of the tendency for changes over the South Pacific to lead the SO lies in the probable role of associated processes in setting up tropical sea surface temperature anomalies, especially during the onset stage of El Niño events. The South Pacific Convergence Zone (SPCZ) is regarded as a key feature, and the physical mechanisms likely to be important are discussed. It is noted that the SO and El Niño events do not always coincide. Tropical Pacific sea surface temperatures can be anomalously warm without a change in the SO, apparently provided that the SPCZ is not involved to any extent. However, global-scale atmospheric teleconnections are primarily associated with the SO.

The role of the atmospheric circulation in climate change is examined. A review is given of the information available in the past record on the atmosheric circulation and its role in climate change, firstly at the surface via sea level pressure in both the northern...

No abstract is provided for this article.