GAME Water and Energy Balance Study interim report

(25 June 2003, revised 18 July 2003)

Kooiti MASUDA
Frontier Research System for Global Change
Yokohama 236-0001, Japan

Water and Energy Balance Study (WEBS) is an activity under GEWEX Hydrometeorological Panel (GHP) to integrate activities of Continental Scale Experiments (CSEs) of which GAME is a member. Since autumn of 2002, Dr. B.J. Sohn (Seoul National University, Korea) and I joined the GAME International Science Panel to promote WEBS.

The purpose of WEBS can be summarized as follows from my viewpoint augmented with ideas given by Dr. Sohn.

We want to know the global energy and water cycle quantitatively. For that goal, we must use some global data sets. Most of them are not direct observations, but either compiled from satellite observations or produced by data assimilation with numerical weather prediction models. In order to have good global budgets, we should evaluate the global data sets with more direct observations. The comparison can be useful to both selection of global data sets to be used immediately, and to improvement of global data sets in the next generation.
A CSE can reveal climatic and hydrological characteristics of that region much better than before. Then, it will be fruitful to compare CSEs in different climatic zones along the same axis of water and energy balance components, in order to build up knowledge about diversity and commonness of water and energy cycle over the globe.
We recommend the synthesis of all available measured and numerically-derived values to understand water and energy balance over the monsoon region. This may be one way to utilize data collected during the GAME Phase 1 for seeking scientific outcomes. For example, we can calculate the continental-scale cloud-radiation interactions by combining the satellite observations such as ISCCP with GAME reanalysis products from which the evolution of radiation energy budget can be examined in conjunction with the monsoon progress.

WEBS activity in GAME has started about two years before that under the leadership of Dr. Toshio Koike (Univ. of Tokyo). We call this phase "GAME WEBS Phase 1" (and the present phase "Phase 2"). Status report in the early part of Phase 1 was made by Koike (2001). Since then, about fifteen researchers in Japan who study water and energy balance with GAME data met together and presented their results. I cannot mention all of them and just name a few of them.

T. Koike and S. Nakane (Univ. of Tokyo) made energy and water budgets of atmospheric column at the positions of radiosonde observations (Nagqu, Gerze and Shiquanhe) in Tibetan Plateau in pre-monsoon (10 May - 15 June) and monsoon (15 June - Aug 9) periods of 1998. This study used surface flux observations, top-of-atmosphere radiation from TRMM CERES, and vertical profile of meteorological variables obtained by radiosondes. Advection terms were obtained as residual. (They also examined advection terms derived from two versions of NCEP reanalysis, which did not agree with the residual estimates.) They found horizontal divergence of energy from the studied areas in the both periods. They also found no significant net divergence of moisture, and that precipitation and evaporation nearly balanced, in the monsoon period.
Xu and Haginoya (2001) obtained surface energy balance components based on conventional meteorological observations at stations over the Tibetan Plateau for 1997. They are conducting similar studies for the year 1998.
Yatagai et al. (2003) compared surface energy fluxes obtained by atmospheric data assimilation (GAME Reanalysis) and surface observations (AAN = Asian Automated weather station Network).
Tanaka et al. (2001) made land-surface data assimilation for HUBEX. They ran a land-surface model (SiBUC) with forcing derived from satellite and meteorological observations.

GEWEX WEBS activity is chaired by Dr. John Roads (Scripps Institution of Oceanography, USA), who is now also the chairperson of GHP. Roads had played an important role in the synthesis of water and energy balance obtained during the GEWEX Continental-scale International Project (GCIP) conducted in the Mississippi river basin. He edited a CD-ROM for GCIP WEBS (Roads et al. 2002a), including water and energy balance products both global-scale and regional-scale, and both observational and model-derived. He participated in comparative studies for GCIP (e.g. Maurer et al. 2001). On the other hand, he also discussed water and energy balance of all CSE regions with global data only (Roads, 2002, Roads et al., 2002b).

A GEWEX WEBS workshop was held in New York in September 2002, in conjunction with GHP meeting. There, Roads suggested to all CSEs to do something like GCIP WEBS and then we should synthesize. It seemed me (and other participants) that we need a nearer target. At the end of that meeting, We agreed upon doing comparison between CSE data sets and some common set of global data. The concept was somewhat refined at the occasion of IUGG Assembly in Sapporo in July 2003. Though not officially claimed, I wish to call this part "GEWEX WEBS Initiative 1".

GEWEX WEBS Initiative 1 is a comparison between global data sets and CSE data sets with respect to water and energy balance, at time resolution of a month. The time frame is July 1996 - June 2001 (5 years), but periods of actual comparison depend on availability of both CSE and global data. The spatial resolution is not explicitly specified, but the effective resolution is limited by that of global data sets which are typically in 2.5 degree latitude/longitude grids. The principal budgets to be considered are those of water and energy in vertically integrated columns. For CSE data sets, not only direct observations but also assimilation with atmospheric and/or land models should be included.

I call it "GEWEX WEBS Initiative 1" because this is just the first short-term goal. It is obviously not very satisfactory.

Monthly time resolution is surely too coarse for such subject as the onset of monsoon in the tropics or the changes in evapotranspiration following phenology in Siberia.
We are interested not only in vertically integrated budgets but also vertical distribution of condensation heating, radiative heating/cooling, clouds, etc.
Just comparison does not give so much insight about the nature. We should also do studies to understand processes.

So I hope for those who are interested in deeper studies to propose Initiatives 2, 3, ... not waiting for the end of Initiative 1. I will insist on the Initiative 1 until it produces some substantial results and also I would like for those who are interested in this initiative to participate.

Vertically integrated budget equations can be written as follows (though some are not exact):

Mass balance of water on an area of land (preferably a river catchment)
dS/dt = P - E - R
Mass balance of water vapor in an atmospheric column
dW/dt = E - P + C
Energy balance at the surface
G = R_net,sfc - H - L E
Total energy balance in an atmospheric column
d(e_d + L W)/dt = R_net,top - G + (C_d + L C)
"Dry" energy balance in an atmospheric column
de_d/dt = R_net,top - R_net,sfc + H + L P + C_d

where S is terrestrial water storage, W is water vapor content in the atmosphere, P is precipitation, E is evaporation from surface, R is runoff, C is convergence of horizontal transport of water vapor in the atmosphere, ) e_d is "dry" energy content in the atmosphere, R_net,top is net downward radiation at the top of the atmosphere, R_net,sfc is net downward radiation at the surface, G is net downward energy flux at the surface (conduction below land surface), H is net upward sensible heat flux at the surface, C_d is convergence of horizontal transport of "dry" energy in the atmosphere, and L is latent heat of vaporization of unit mass of water.

The choice of global data set is based partly on the fact that this is a part of GEWEX, and partly from popularity among water and energy balance researchers. Of course, we can also compare other global data sets.

For precipitation, GPCP (Global Precipitation Climatology Project) products are preferred. Monthly merged satellite-gauge product (Huffman et al., 1997) at 2.5 degree grids is available for the period from 1979 to present.
For radiative fluxes at surface, though GEWEX SRB (Surface Radiation Budget) project is ongoing, the time frame of the product (1986-1995) does not cover most of Intensive Observing Periods (IOPs) of CSEs. On the other hand, Zhang and Rossow (2002), main producers of International Satellite Cloud Climatology Project (ISCCP) data sets, also made radiative flux data set (called "FD"), covering July 1983 to June 2001 at 3 hour time resolution and about 2.5 degree spatial resolution. The values were calculated by radiative transfer equations with cloud information of ISCCP as input. We can use this data set.
For water vapor, though there is no official GEWEX data set, Product of NASA Water Vapor Project (NVAP, Randel et al. 1996) is available for the period 1988 - 1999 at daily time resolution and 1 degree spatial resolution.
For runoff, we can use river discharge data compiled by Global Runoff Data Centre (GRDC). GRDC also collaborated with University of New Hampshire to produce climatological 0.5-degree grid values of runoff.
For energy and water vapor transport by the atmosphere, there is no official GEWEX data set, and we depend on some product of atmospheric four-dimensional data assimilation. NCEP Reanalysis 2 (Kanamitsu et al., 2002) will be used as a common reference.

Now we should think about what comparison can be made with GAME data. I mainly list those which seem to be useful for "Initiative 1", but also include some other interesting ones.

One kind of study that should be done is to make atmospheric energy and water budget using observation only, without depending on forecast models. Such studies are needed because it is questionable that present forecast models handle processes such as precipitation where diurnal variation and orographic effects are significant. It is also preferable that the atmospheric water balance can be compared with river basin water balance. Though radiosonde observations are made at 6-hour interval at many locations during GAME IOP, it seems that few budget studies have been done. One known example is energy and water budgets with radiosondes of GAME-Tropics by Azuma and Tachibana (2002), though their time frame is smaller than one month. It seems that the radiosonde observation network is largely determined by logistics and not ideal for budget studies even though they seem to be adequate for profile studies. But probably something can be done, especially for HUBEX, and I hope anyone interested would volunteer.
Though somewhat model-dependent, atmospheric data assimilation products in which enhanced observations are incorporated are also important source of CSE energy and water budgets. GAME Reanalysis version 1.1 and 1.5 are produced (see Yamazaki et al., 2003). They are global atmospheric analyses covering the period from April to October 1998. Ueda et al. (2003) made three-dimensional atmospheric dry and latent energy budgets based on GAME Reanalysis 1.1. Masuda (2003a) made preliminary evaluation of water balance components of GAME Reanalysis 1.5. Another ongoing activity is GAME/HUBEX Regional Reanalysis (Wakatsuki et al., 2003).
Radiative fluxes at the top of the atmosphere is observed by TRMM CERES though the time frame is just January to August 1998 and the spatial domain is equatorward of 35 degrees latitudes. Preliminary comparison suggests that there is systematic difference between CERES and FD for longwave fluxes, though it is small for shortwave fluxes.
River runoff data should be collected and examined. It can be used to check quality of moisture convergence derived from atmospheric data (if steady state can be assumed), and then evaporation and terrestrial water storage can be evaluated as residual. Fukutomi et al. (2003) reported some signal in interannual variability of water balance component over the Lena river basin.
For energy fluxes at surface, there are generally no direct observations known to be representative of scales comparable to grid size of global data (about 250 km). Nevertheless, comparison with direct observation is important in evaluation of global data sets. AAN data (Nohara et al., 2003) provide a collection of flux observation with good continuity (mostly 1998 - 2000). Masuda (2003b) made an initial attempt to compare radiative fluxes at surface between AAN and FD data sets.
To know spatial variability of surface fluxes and some state variables (such as soil moisture), we should also utilize land-surface models (e.g. Tanaka et al., 2001).
Precipitation is observed by several ways: raingauges, radars and satellites. Collection of operational raingauge data by GAME-Tropics revealed features of precipitation distribution with spatial scale smaller than about 500 km which are not depicted by global data sets such as GPCP as well as GAME Reanalysis (Masuda, 2003a). TRMM PR is promising in obtaining vertical distribution of condensation heating that can be compared with three-dimensional budgets of dry energy and latent energy in the atmosphere. Mori et al. (2002) produce a data set of condensation heating using the algorithm of Satoh and Noda (2001).

The list is not exhaustive and probably I miss something relevant. Please let me know about your activities, comments, suggestions, etc.

References

(Items marked with (J) are texts in Japanese.)
Azuma, E. and Y. Tachibana, 2002: Estimation of heat and moisture budgets and surface turbulent heat flux based on rawinsonde observations in Indochina. presented at 2002 Workshop on GAME-T.
Fukutomi, Y., H. Igarashi, K. Masuda and T. Yasunari, 2003: Interannual variability of summer water balance components in three major river basins of northern Eurasia. J. Hydrometeorol., 4, 283 - 296.

Huffman, G.J., R.F. Adler, P.A. Arkin, A. Chang, R. Ferraro, A. Gruber, J. Janowiak, R.J. Joyce, A. McNab, B. Rudolf, U. Schneider, and P. Xie, 1997: The Global Precipitation Climatology Project (GPCP) Combined Precipitation Data Set. Bull. Amer. Meteor. Soc., 78, 5 - 20.
Kanamitsu, M., W. Ebisuzaki, J. Woollen, S.-K. Yang, J. Hnilo, M. Fiorino, and J. Potter, 2002: NCEP/DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83, 1631 - 1643.
Koike, T., 2001: Status report on the GAME Water and Energy Budget Study (GWEBS), Proc. Int'l Workshop on GAME-AAN/Radiation, 24.

Masuda, K., 2003a: Evaluation of precipitation of GAME Reanalysis on continents (J). Proc. 2003 Spring Meeting of Meteorol. Soc. Japan, No. P467. (English version available at http://www.jamstec.go.jp/frsgc/research/d2/masuda/gamerean/index.html)
Masuda, K., 2003b: Comparison between station-based and satellite-based observations of radiative fluxes at surface in monthly mean basis. (http://www.jamstec.go.jp/frsgc/research/d2/masuda/fd_aan/index.html, also included in Nohara et al. (2003).)
Maurer, E.P., G.M. O'Donnell, D.P. Lettenmaier, and J.O. Roads, 2001: Evaluation of the land surface water budget in NCEP/NCAR and NCEP/DOE Reanalyses using an off-line hydrologic model. J. Geophys. Res., 106, 17841-17862.
Mori, S., S. Satoh, M. Katsumata, Y.-M. Kodama and H. Ueda, 2002: Construction of TRMM 2A25 dekad data set for understanding of monsoon precipitation system (J). Proc. 2002 Autumn Meeting of Meteorol. Soc. Japan, No. C355.
Nohara, D., S. Miyazaki, M. Sugita, T. Yamanaka, F. Kimura and T. Yasunari (eds.), 2003: GAME Asian Automatic Weather Station Network (AAN) Data CD Ver. 1.0 (through year 2000). CD-ROM (GAME CD No. 6). (See also http://www.suiri.tsukuba.ac.jp/Project/aan/aan.html).
Randel, D.L., T.H. Vonder Haar, M.A. Ringerud, G.L. Stephens, T.J. Greenwald and C.L. Combs, 1996: A new global water vapor dataset. Bull. Amer. Meteorol. Soc., 77, 1233 -- 1246.
Roads, J., 2002: Closing the Water Cycle. GEWEX News, 12, No. 1, 1 and 6-8.
Roads, J. et al. eds., 2002a: GEWEX Continental-scale International Project (GCIP) Water and Energy Budget Synthesis (WEBS) 1996-1999}. CD-ROM. (Available from International GEWEX Project Office (gewex@gewex.org), See also http://ecpc.ucsd.edu/gcip/gcipwebs.html).
Roads, J., M. Kanamitsu and R. Stewart, 2002b: CSE water and energy budgets in the NCEP-DOE Reanalysis II. J. Hydrometeorol., 3, 227 - 248.
Satoh, S., and A. Noda, 2001: Retrieval of latent heating profiles from TRMM radar data. Proc. 30th Conf. on Radar Meteor., Munich, Germany, Amer. Meteor. Soc., 340-342.
Tanaka, K., O. Kozan, T. Nakamura, M. Shiiba and S. Ikebuchi, 2001: Land data assimilation in the GAME-HUBEX. 5th Int'l Study Conference on GEWEX in Asia and GAME, 697 - 702.
Ueda, H., H. Kamahori and N. Yamazaki, 2003: Seasonal contrasting features of heat and moisture budgets between the eastern and western Tibetan Plateau during the GAME IOP. J. Climate, 16, in press.
Wakatsuki, Y., K. Tsuboki, T. Kawahata and H. Nakamura, (2003): Production of GAME/HUBEX Regional Reanalysis data set (J). Proc. 2003 Spring Meeting of Meteorol. Soc. Japan, No. P428.
Xu, J. and S. Haginoya, 2001: An estimation of heat and water balances in the Tibetan plateau. J. Meteorol. Soc. Japan, 79, 485 - 504.
Yamazaki, N., K. Takahashi and A. Yatagai, 2003: Report on the GAME Reanalysis. GAME Phase 1 Summary Reports (GAME Publ. No. 37), 81 - 87. (See also http://gain-hub.mri-jma.go.jp/GAME_reanal.html).
Yatagai, A. M. Sugita, N. Yamazaki, M. Oh'izumi, 2003: A comparative study of the surface fluxes derived from meteorological four dimensional data assimilation products (GAME Reanalysis) with Asian Automatic Weather Station Network (AAN) observations over the Tibetan Plateau. Proc. APHW2003, Asia Pacific Association of Hydrology and Water Resources, 722 - 727.
Zhang, Y. and W.B. Rossow, 2002: New ISCCP global radiative flux data products. GEWEX News, 2, No. 4, 7. (See also http://isccp.giss.nasa.gov/projects/flux.html).