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J. T. Kiehl and Kevin E. Trenberth

The purpose of this paper is to put forward a new estimate, in the context of previous assessments, of the annual global mean energy budget. A description is provided of the source of each component to this budget. The top-of-atmosphere shortwave and longwave flux of energy is constrained by satellite observations. Partitioning of the radiative energy throughout the atmosphere is achieved through the use of detailed radiation models for both the longwave and shortwave spectral regions. Spectral features of shortwave and longwave fluxes at both the top and surface of the earth's system are presented. The longwave radiative forcing of the climate system for both clear (125 W m−2) and cloudy (155 W m−2) conditions are discussed. The authors find that for the clear sky case the contribution due to water vapor to the total longwave radiative forcing is 75 W m−2, while for carbon dioxide it is 32 W m−2. Clouds alter these values, and the effects of clouds on both the longwave and shortwave budget are addressed. In particular, the shielding effect by clouds on absorption and emission by water vapor is as large as the direct cloud forcing. Because the net surface heat budget must balance, the radiative fluxes constrain the sum of the sensible and latent heat fluxes, which can also be estimated independently.

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K. M. Lau, C. H. Sui, and W. K. Tao

This paper presents the preliminary findings of an investigation of the water budget of tropical cumulus convection using the Goddard Cumulus Ensemble Model (GCEM). Results of an experiment designed to obtain a “fingerprint” in the tropical hydrologic cycle in response to surface warming are also presented. The ensemble mean water budget shows that the distribution of water vapor and cloud water in the tropical atmosphere is maintained as a result of a balance between moisture convergence (including cloud scale and large scale) and condensation and reevaporation by various microphysical species within the cumulus clusters. Under radiative convective equilibrium conditions, 66% of the precipitation reaching the ground comes from the convective region and 34% from the stratiform region. In a climate with above-normal sea surface temperature but fixed large-scale vertical velocity, tropical convection is enhanced with more abundant moisture sources. Water vapor is increased throughout the troposphere with the surplus largest near the surface and decreases monotonically up to 10 km. However, the percentage increase in water vapor is largest near 8 to 16 km. As a result of the warming, the freezing level in clouds is elevated resulting in a large increase (decrease) in cloud water just above (below) 5 km. As with water vapor, the fractional increase in cloud water and cloudiness amount is largest at the upper troposphere.

In spite of the detailed microphysics and cloud-scale dynamical processes included in the GCEM, the results on changes in temperature and water vapor induced by surface warming are in agreement with those from general circulation models that use crude cumulus parameterization. This is consistent with previous findings that equilibrium water vapor distribution is a strong function of temperature. In an open domain such as the tropical convective environment, with a specified climatological vertical velocity, the ratio of increased precipitation to increased surface evaporation due to a 2°C surface warming is approximately 5. The increase is mostly found for convective rain and is negligible for stratiform rain. The climate implication of these changes is also discussed.

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Kevin E. Trenberth, John T. Fasullo, and Jeffrey Kiehl

An update is provided on the Earth's global annual mean energy budget in the light of new observations and analyses. In 1997, Kiehl and Trenberth provided a review of past estimates and performed a number of radiative computations to better establish the role of clouds and various greenhouse gases in the overall radiative energy flows, with top-of-atmosphere (TOA) values constrained by Earth Radiation Budget Experiment values from 1985 to 1989, when the TOA values were approximately in balance. The Clouds and the Earth's Radiant Energy System (CERES) measurements from March 2000 to May 2004 are used at TOA but adjusted to an estimated imbalance from the enhanced greenhouse effect of 0.9 W m−2. Revised estimates of surface turbulent fluxes are made based on various sources. The partitioning of solar radiation in the atmosphere is based in part on the International Satellite Cloud Climatology Project (ISCCP) FD computations that utilize the global ISCCP cloud data every 3 h, and also accounts for increased atmospheric absorption by water vapor and aerosols.

Surface upward longwave radiation is adjusted to account for spatial and temporal variability. A lack of closure in the energy balance at the surface is accommodated by making modest changes to surface fluxes, with the downward longwave radiation as the main residual to ensure a balance.

Values are also presented for the land and ocean domains that include a net transport of energy from ocean to land of 2.2 petawatts (PW) of which 3.2 PW is from moisture (latent energy) transport, while net dry static energy transport is from land to ocean. Evaluations of atmospheric reanalyses reveal substantial biases.

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K.-M. Lau, J. H. Kim, and Y. Sud

Results of an intercomparison study under the Atmospheric Model Intercomparison Project (AMIP) to assess the abilities of 29 global climate models (GCMs) in simulating various aspects of regional and hydrologic processes in response to observed sea surface temperature and sea ice boundary forcings are presented. The authors find that the models generally portray an earthlike climate to approximately 10%–20% of the global land surface temperature (= 14.8°C) and global precipitation (= 2.3 mm day−1) While a majority of the models have a reasonable global water budget, about a quarter of the models show significant errors in the total global water balance.

While the model frequency distributions of heavy precipitation associated with deep convection are in reasonable agreement with observations, a systematic underestimate of the frequency of occurrence of light precipitation events (< 1 mm day−1) is present in almost all the AMIP models, especially over continental desert regions and over tropical and subtropical oceanic regions contiguous to the west coasts of continents where low-level stratocumulus clouds tend to occur. This discrepancy is presumably related to the crude treatment of moist processes, especially those related to low clouds and nonconvective precipitation in the models. Another common problem in the global rainfall distribution is the presence of spectral rain or spurious gridpoint-scale heavy rain. The artificial anchoring of rainfall to topographic features in the Maritime Continent appears to be a generic problem in many GCMs. Models differ substantially in the magnitude of the rainfall amount over the eastern Pacific ITCZ for all seasons. The simulated boreal summer rainfall distributions have large variability over the Indian subcontinent and the Bay of Bengal. The northward migration of the monsoon convective zones are not well simulated. In particular, the East Asian monsoon rainband over the subtropical western Pacific is ill-defined or absent in all models.

On the interannual timescale, the models show reasonable skills in simulating the fluctuations of the Southern Oscillation and the eastward migration of the major equatorial precipitation zone during ENSO. Most models show useful rainfall prediction skill in the Tropics associated with ENSO-related SST forcing. However, the models do not show any useful skill for extratropical rainfall prediction from specified anomalous global SST forcing. Overall, the models depict a reasonably realistic annual cycle of water balance over regions where long-term local moisture balance is maintained—that is, (P–E) ≈ 0—over large interior land regions in the extratropics. In regions of strong dynamic control—that is, (P–E) >>0—such as the tropical western Pacific, monsoon regions, and the ITCZ, the intermodel variability is very large.

The simulated water balance over large river basins has been validated against hydrographic river discharge data using a river-routing model. Results show that while the model ensemble mean runoffs are consistent with the climatological observed river discharge for the Amazon and Mississippi, the intermodel variability is substantial. The models yield even more divergent results over other world river basins. These results suggest that while some GCMs may have moderate capability in capturing some aspects of the climatological variation of runoff, it is premature to use them for climate studies related to continental-scale water balance. A ranking of the AMIP models and some possible implications based on the above performance are also presented.

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Katja Friedrich, Robert L. Grossman, Justin Huntington, Peter D. Blanken, John Lenters, Kathleen D. Holman, David Gochis, Ben Livneh, James Prairie, Erik Skeie, Nathan C. Healey, Katharine Dahm, Christopher Pearson, Taryn Finnessey, Simon J. Hook, and Ted Kowalski

-levels-lake-mead-reach-record-lows/story?id=39235749 . Jacoby , G. C. , Jr. , R. A. Nelson , S. Patch , and O. L. Anderson , 1977 : Evaporation, bank storage, and water budget at Lake Powell. National Science Foundation Lake Powell Research Project Bulletin 48, 98 pp. Kondo , J. , 1994 : Meteorology of the Water Environment—Water and Heat Balance of the Earth’s Surface (in Japanese). Asakura Shoten Press, 348 pp. Langmuir , I. , and V. J. Schaefer , 1943 : Rates of evaporation of water through compressed monolayers on water

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Xin Li, Guodong Cheng, Shaomin Liu, Qing Xiao, Mingguo Ma, Rui Jin, Tao Che, Qinhuo Liu, Weizhen Wang, Yuan Qi, Jianguang Wen, Hongyi Li, Gaofeng Zhu, Jianwen Guo, Youhua Ran, Shuoguo Wang, Zhongli Zhu, Jian Zhou, Xiaoli Hu, and Ziwei Xu

, though not difficult in principle, still involves great uncertainties in the measurement and estimation methods used to study many water cycle components. Evapotranspiration might be the most uncertain component. Its measurement using the EC technique is challenged by the energy balance closure problem ( Foken 2008 ); its remote sensing estimation is far from reaching a mature stage ( NRC 2008a ). Precipitation, in both cold and arid regions, features great spatiotemporal heterogeneity. Reliable

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F. M. Ralph, M. Dettinger, D. Lavers, I. V. Gorodetskaya, A. Martin, M. Viale, A. B. White, N. Oakley, J. Rutz, J. R. Spackman, H. Wernli, and J. Cordeira

roles that ARs play in water resources, aquatic and terrestrial ecosystems and vegetation, seasonal snowpacks, and groundwater recharge. Finally, ARs critically affect the mass balances of the Antarctic and Greenland Ice Sheets, balances that will do much to define the extent and rate of sea level rise in centuries to come. AR applications. The emerging understanding of ARs, from monitoring to dynamics and impacts, has led to a number of application areas, a few of which are highlighted here. A

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Ghassem Asrar, Sandrine Bony, Olivier Boucher, Antonio Busalacchi, Anny Cazenave, Mark Dowell, Greg Flato, Gabi Hegerl, Erland Källén, Teruyuki Nakajima, Alain Ratier, Roger Saunders, Julia Slingo, Byung-Ju Sohn, Johannes Schmetz, Bjorn Stevens, Peiqun Zhang, and Francis Zwiers

energy and water balance. Those observations are also essential for capturing the intensity and frequency of precipitation and their extremes, as well as land–atmosphere feedbacks relevant to water and temperature related extremes. 9) Space-based observations of the cryosphere need to deliver both area and volume measurements in order to narrow down uncertainties in the mass balance and changes. The results help us to better formulate ice sheet modeling. 10) Understanding ocean circulation and

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Jean-Claude André, Jean-Paul Goutorbe, and Alain Perrier

is used to calculate the sensible heat flux from thetemperature and wind-velocity gradients. The evaporationflux is then obtained by balancing the surface-energy budget.Each station also includes a recording rain gage in order tomonitor the local water budget. Neutron probe measurements of the soil moisture are made around each stationonce every 8-10 days. The intent is to provide a sufficientsampling of the spatially variable evaporation flux continuously throughout the experiment, so as to

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Andrew D. Gronewold and Vincent Fortin

As one of the Earth's largest surface freshwater resources, the North American Laurentian Great Lakes are an ideal test bed for understanding water balance dynamics of large hydrologic systems and for establishing effective protocols for collaborative binational water resources and ecosystem services research. To leverage ongoing and future federal government research efforts in the Great Lakes region, representatives from the National Oceanic and Atmospheric Administration (NOAA), the

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