NUMERICAL SIMULATION OF A CANOPY SCALE TEMPERATURE VARIATION IN TOKYO

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1 NUMERICAL SIMULATION OF A CANOPY SCALE TEMPERATURE VARIATION IN TOKYO Hiroaki Kondo,* Yutaka Genchi,* Akihiro Kanazaa,**Yukihiro Kikeaa, and Hiroshi Koiyaa * National Institute of Advanced Industrial Science, Tsukuba, Japan; **NTT Corporation, Tokyo, Japan Fuji Research Institute Corporation, Tokyo, Japan, University of Tokyo, Tokyo, Japan Abstract A cobined odel of a esoscale eteoroloical odel ith an urban canopy odel as applied to a central business area in Tokyo, Japan to investiate the daily teperature variation and its perforance The odel is a one-ay nested odel The esoscale odel is NIRE-MM hich is nuded ith the JMA-RSM The canopy odel is a vertically one-diensional odel, hich requires inforation about the averaed sky-vie factor, the floor density of the buildins, and the vertical distribution of anthropoenic heat source in the area under consideration The results ere copared ith the observational data at a sall priary school in the business district in Tokyo durin suer days The perforance depends on the area under consideration in the canopy odel When the area under consideration in the canopy odel as 500 square, the perforance as not so ood Hoever, hen the area as reduced to the school only (approxiately 60 square), the perforance becae fairly ood In other ords, the observation in the priary school represents the teperature in the area of its schoolyard 1INTRODUCTION There have been any icro-eteoroloical easureents in urban areas Hoever, the structure of the city, the netork of the road, and the location of the anthropoenic heat sources are very coplicated This eans that both natural and artificial heat sources are coplexly located and that it is very difficult to estiate the source area (foot print) of the point observation fro the observation in the urban area We have been developin a cobined odel of a esoscale urban cliate odel, an urban canopy odel and a buildin enery consuption odel (Kondo and Liu, 1998; Kondo and Kikeaa, 2003) The present urban canopy odel in the cobined odel requires paraeters, includin the density of the buildins and the averaed idth of buildins etc in the area under consideration These paraeters depend on the area under consideration We investiated and copared the differences beteen the point observation data and calculated data by chanin the idth of the area under consideration 2MODEL 21Atospheric layer The odel consists of a one-diensional diffusion equation for the oentu, potential teperature and specific huidity In the oentu equation, diffusion and dra ters are considered (Kondo and Akashi, 1976, Sorbjan and Sorbjan and Uliasz, 1982, Uno et al, 1989) u 1 u cau z 2 u + 2 v + f ( v v ) + ( u ) 1 O ( u u ) + ( v ) v 1 v 2 2 cav u + v f (2) 2 O Here, u, v are the ind velocities in the east-est and north-south coponent, respectively We usually consider an urban block of up to 1k square in hich the buildin botto has the sae square area The lenth of the square is assued as b and the distance beteen the buildins is assued as d We assue that the four buildin sidealls are exactly directed north, south, east, and est The heiht of the buildin is not unifor, but (1)

2 the distribution of the heiht can be considered We define the rate of the actual buildins hich occupy level z to all the buildins ( 0 P b 1) P b = 0 eans there is no buildin at level z and P b = 1 eans all the buildin area at z is actually occupied by buildins Then, 2 1 b b Pb = P ( d b) 2 b (3) a = (4) ( b + d) b Pb c is a coefficient, f is the Coriolis paraeter, and u, v are the eostrophic ind The equations for potential teperature and specific huidity are, θ 1 θ QAS h ( θ O ) (5) c p ρ qv 1 qv QAL q ( qvo ), (6) lρ here θ, q v, QAS, and Q AL are the potential teperature, the specific huidity, the anthropoenic sensible heat and the anthropoenic latent heat, respectively c p is the specific heat of air, ρ is the air density and l is the latent heat of vaporization The last ters in Eqs(1),(2),(5) and (6) are the effect fro outer reion, if necessary Nudin or the Netoninan ethod is used for the The suffix O eans the value in the outer reion In the atosphere, the turbulent diffusion coefficients are used Gabo s forula (Gabo, 1978) is used for R f R fc, here R f the flux Richardson nuber and R fc = 0 29 is the critical Richardson nuber The scale lenth L in the forula is iven by Watanabe and Kondo (1990), 3 1 z L = 2κ {1 exp( κη)}, η = ca (7) 3 ca 2κ here κ is the Karan constant L is liited by Blackadar s forula (Blackadar, 1968), κz L, L0 = 100 κz 1+ L 0 2 U When R f > R fc, K = K h = K q = L, z here L is calculated by (7) but the axiu value is set at Radiaition Althouh the odel is one-diensional, the heat budet at the surface is considered on the round, roof, and at each level of the buildin alls in four directions, separately The folloin equation is solved on each surface dt c ρ δ = RN + Q + le + G (8) dt here c and ρ are the heat capacity and density of the buildin s all, roof or round, T is the teperature of the all, roof or round surface, δ is the thickness of the first layer, R N, Q, le, and G, are the net radiative flux, sensible heat flux and latent heat flux hich are released fro all, roof or round surface, and the heat flux retained in the buildin all hich partly intrudes into the roos in the buildins or in the round For the short ave, e consider direct solar insolation, diffused solar insolation fro the sky, and reflection fro the surface The reflection is considered only once Diffused solar insolation is considered as isotropic Kondo s forula (1994) as used for direct solar insolation and for lobal solar insolation Vie factors are not calculated exactly but obtained ith soe eoetric approxiations (Kondo and Liu, 1998) These radiations are first defined for the riid buildins After that, the rate of reflection and transission throuh the buildins are considered accordin to P b (z) A lon-ave fro the atosphere and a re-eission fro each surface are considered in the odel Lon-ave radiation fro the atosphere is considered as isotropic and Kondo s forula (1994) as also used Re-eission is considered only once Lon-ave radiation is also defined for the riid buildins first and the rate of

re-eission and transission throuh the buildins are considered accordin to P b (z) 23Surface fluxes The sensible heat flux Q is calculated ith Jures s forula (Jures, 1924) ith a rouh surface hen the

3 re-eission and transission throuh the buildins are considered accordin to P b (z) 23Surface fluxes The sensible heat flux Q is calculated ith Jures s forula (Jures, 1924) ith a rouh surface hen the surface teperature is hiher than the air teperature Q = α ( T S Ta ) (9) here T a is the teperature of the atosphere When T S < Ta, the usual Monin-Obukhov theory is used because (9) ay overestiates the flux in stable condition For the calculation of the latent heat flux, plant canopy conductance is introduced Then, E GaGS = ( qvs ( TS ) qv ( Ta )) (10) ρ Ga + GS here G a is the aerodynaic conductance, GS is the plant canopy conductance and q vs ( T S ) is the saturated specific huidity at T S The heat retained in the all of the buildins and in the round is calculated ith a one-diensional theral conduction equation T T = κ n n (11) / n eans the derivative noral to the surface and κ is theral diffusivity of the all or the round 3CALCULATION The calculation is desined for an observation at the schoolyard of a priary school in the central district in Tokyo The GIS ap is shon in Fi1 Here e calculate the teperature variation at the school The canopy odel requires paraeters; b, d, P b (z) and so on First e calculate the teperature ith the paraeters that are averaed over 500 square around the observational point in the priary school We then reduce the averain area to the school only and copare the results The used paraeters are shon in Table 1 The calculation as ade fro July 20 to 23, 1997 The eteoroloical condition in the outside of the canopy is calculated ith a esoscale odel (NIRE-MM) The ososcale Table 1 Canopy paraeters used in the calculation The floor density is iven for the loest 33 in the table 500 area school only b Pb(1-3) 1 1 Pb(3-6) Pb(6-9) Pb(9-12) Pb(12-15) 09 0 Pb(15-18) Pb(18-21) Pb(21-24) Pb(24-27) Pb(27-30) Pb(30-33) Fi1 GIS ap of the central district in Tokyo The star sybol is the taret priary school (Sakaoto priary school) odel used the data of the RSM odel product, JMA as the boundary and nudin conditions 4RESULTS The observed teperature and to calculated

4 teperature variations are shon Fi2 The teperature calculated ith the paraeters averaed over 500 square is not in very ood areeent ith the observation at the school On the other hand, the calculation ith the paraeter of the school only is in ood areeent ith the observation This eans that the observation at the schoolyard is representative of the area of its schoolyard scale Teperature( o C) CAL500 OBS CALschool TIME(hours) Fi2 Coparison of the teperature variation at the Sakaoto priary school in Tokyo CAL500 is the result of the canopy odel calculation ith the paraeters averaed over the 500 square area around the school CALschool is the sae as CAL500 except that the paraeters are averaed over the school only No anthropoenic heat is considered ACKNOWLEDGEMENT This study as supported by the Proposal-Based Ne Industry Creative-Type Technoloy R&D Prootion Prora fro the Ne Enery and Industrial Technoloy Developent Oranization (NEDO) of Japan and by the Ministory of the Environnt, Japan References Blackadar,AK 1968, The vertical distribution of ind and turbulent exchane in neutral atosphere, J Geophy Res,67, Gabo,K 1978, Notes on the turbulence closure odel for atospheric boundary layers, J Meteor Soc of Japan, 56, Jures,W 1924, Der Wareubereran an einer ebenen Wand, Beihefte zu Gesundheits-Inenieur, Beiheft 19, Nov (in Geran) Kondo,J(ed), 1994, The eteoroloy of a ater environent, Asakura-shoten, p350 (in Japanese) Kondo,H, and Kikeaa, Y, 2003: Teperature variation in the urban canopy ith anthropoenic enery use, Pure and Appl Geophs 160, Kondo,H and Liu, FH, 1998, A study on the urban theral environent obtained throuh a one-diensional urban canopy odel, J Jpn Soc Atos Environ, 33, (in Japanese) Sorbjan,Z and Uliasz,M,1982, Soe nuerical urban boundary-layer studies, Boundary-Layer Met, 22, Uno, I, Ueda,H and Wakaatsu,S, 1989,Nuerical odelin of the nocturnal urban boundary layer, Boundary-Layer Met, 49, Watanabe, T and JKondo, 1990, The influence of canopy structure a nd density upon the ixin lenth ithin and above veitation, J Meteor Soc Japan,68,

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