Hirofumi Sugawara

Roughness lengths for momentum and heat derived from outdoor urban scale models

Abstract Urban climate experimental results from the Comprehensive Outdoor Scale Model (COSMO) were used to estimate roughness lengths for momentum and heat. Two different physical scale models were used to investigate the scale dependence of the roughness lengths; the large scale model included an aligned array of 1.5-m concrete cubes, and the small scale model had a geometrically similar array of 0.15-m concrete cubes. Only turbulent data from the unstable boundary layers were considered. The roughness length for momentum relative to the obstacle height was dependent on wind direction, but the scale dependence was not evident. Estimated values agreed well with a conventional morphometric relationship. The logarithm of the roughness length for heat relative to the obstacle height depended on the scale but was insensitive to wind direction. COSMO data were used successfully to regress a theoretical relationship between κB−1, the logarithmic ratio of roughness length for momentum to heat, and Re*, the roug...

TOKYO METROPOLITAN AREA CONVECTION STUDY FOR EXTREME WEATHER RESILIENT CITIES

The present paper describes background, mission, research topics, and preliminary results of the research project “Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)”. TOMACS is one of the research projects of “Social System Reformation Program for Adaption to Climate Change” which has been started since July 2010 under the “Special Coordination Funds for Promoting Science and Technology” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). TOMACS aims to understand the processes and mechanisms of extreme weather, using dense meteorological observation networks designed in the Tokyo metropolitan district, to develop a monitoring and predicting system of extreme phenomena (MPSEP), and to implement social experiments on extreme weather resilient cities in collaboration with related government institutions, local governments, private companies, and residents. More than 25 organizations and over 100 people participate in the present research projects. One of unique features of TOMACS is utilization of dense meteorological instruments in the Tokyo Metropolitan area which is one of the most urbanized areas in the world. The field campaign in the Tokyo metropolitan area, using research instruments and operational meteorological networks is planned by MRI and thirteen groups in the summers of 2011-2013 to target the tropospheric environment, boundary layer, initiation of convections and lifecycle of thunderstorms. Observation on environmental conditions of convections are carried out using radio sonde, wind profiler, GPS network, unmanned air viecle, and network of automated weather stations. Generation and development of convective precipitations are investigated by observations using Doppler lidar, rapid scan geostationary satellite, Kuband polarimetric radar, X-band polarimetric radar network (X-NET) and C-band research polarimetric radar and C-band operational Doppler radars. Several thunderstorms were captured by the dense meteorological network during 2011 campaign observations. The present paper shows preliminary results of the analysis. Social experiments on extreme weather resilient city using radar networks are also presented.

Thermal Influence of a Large Green Space on a Hot Urban Environment.

City-scale warming is becoming a serious problem in terms of human health. Urban green spaces are expected to act as a countermeasure for urban warming, and therefore better understanding of the micro-climate benefits of urban green is needed. This study quantified the thermal influence of a large green park in Tokyo, Japan on the surrounding urban area by collecting long-term measurements. Apparent variations in the temperature difference between the park and surrounding town were found at both the diurnal and seasonal scales. Advection by regional-scale wind and turbulent mixing transfers colder air from the park to urban areas in its vicinity. The extent of the parks thermal influence on the town was greater on the downwind side of the park (450 m) than on the upwind side (65 m). The extent was also greater in an area where the terrain slopes down toward the town. Even on calm nights, the extent of the thermal influence extended by the park breeze to an average of 200 m from the park boundary. The park breeze was characterized by its divergent flow in a horizontal plane, which was found to develop well in calm conditions late at night (regional scale wind <1.5 m s and after 02:00 LST). The average magnitude of the cooling effect of the park breeze was estimated at 39 Wm. This green space tempered the hot summer nights on a city block scale. These findings can help urban planners in designing a heat-adapted city.

Representative Air Temperature of Thermally Heterogeneous Urban Areas Using the Measured Pressure Gradient

A method to measure an area-averaged ground air temperature based on the hydrostatic equation is shown. The method was devised to overcome the problem of finding the most representative surface air temperature over a wide region, a problem that has seriously hindered the description of urban heat islands. The vertical pressure gradient is used and the hydrostatic equation is applied to estimate the average air temperature between two barometers, which is here called the hydrostatic temperature. The error analysis shows that the hydrostatic temperature can be estimated with a systematic error of 1.88C and a random error of 0.78C in the case in which the two barometers have a vertical separation of 228 m. The measured hydrostatic temperature agreed with the average of the directly measured temperature within 0.78C rms. For this barometer separation, the representative area of the hydrostatic temperature was experimentally found to be a 12-km-radius circle. The size of this area decreased when the vertical separation of the barometers decreased. The hydrostatic temperature is compared with the average directly measured temperature for various areas. The maximum correlation between them occurred for a circular area with a 12-km radius centered on the pressure measurements. The size of the representative area for this method is larger than that for the direct measurement of air temperature.

Surface Albedo in Cities: Case Study in Sapporo and Tokyo, Japan

The surface albedo of two large cities in Japan was measured using a pyranometer mounted on a helicopter to avoid the bidirectional reflectance distribution. The daytime albedo was 0.12 in the cities, which was less than that of a nearby forest (0.16). The albedo was dependent on building structure in the cities; the albedo was lower in areas with more buildings, and decreased as the aspect ratio of street canyons increased. There are two reasons for this dependency: the multiple reflection of radiation in the building canopy, as has been shown in many previous studies, and the sparse vegetation in urban areas. These two factors concurrently determine the albedo in a real city, where the vegetation amount decreases as the plan roof ratio increases.

FIELD MEASUREMENTS ON THE COOLING EFFECT OF THE IMPERIAL PALACE AND ITS THERMAL INFLUENCE ON THE SURROUNDING BUILT UP AREA

In this paper, results are shown from micro-climatological observations performed in and around a largest green space in central Tokyo, “Imperial Palace”, during summer. Its area is 230ha, and it was once the Edo-Castle, then surrounded by a moat.In a clear calm night, the cool air flows out from the Imperial Palace to the surrounding city area gravitationally. Different from the daytime advection by prevailing wind, the turbulent mixing is very weak in nighttime seeping phenomena because of the stable atmospheric condition. In the west side, the cool air flows over the valley of moat (20m depth) and spreads out into the built-up area. In the east side, cool air front sometimes penetrates the adjacent CBD area and reach near the Tokyo Station. The wide streets have a larger effect on cool air seeping than the moat dose even though water temperature is higher than ambient air temperature.

Inflammatory Popliteal Aneurysm

A 67-year-old man was referred to our department because of fever, right lower thigh swelling, and redness with pain. Laboratory tests showed slightly elevated leukocytes and markedly elevated C-reactive protein levels. Computed tomography confirmed a popliteal aneurysm with wall thickening, so-called mantle sign. Aneurysmorrhaphy with a reversed autologous saphenous vein reconstruction was performed. Aneurysm sac and perianeurysm tissue cultures were negative for aerobic and anaerobic bacteria. The microscopic appearance of the aneurysm showed thickening of the adventitia and infiltration of inflammatory cells. This report presents, for the first time, findings suggestive of an inflammatory aneurysm of the popliteal artery.

Evaluation of scintillometery measurements of fluxes of momentum and sensible heat in the roughness sublayer

Scintillometer measurements of turbulent fluxes of momentum and sensible heat in the roughness sublayer over a regular array of cubes in an outdoor environment were tested with direct measurement from sonic anemometers. The dissipation rate, ε, and temperature structure parameter, CT2, obtained from the scintillometer agreed well with those from four sonic anemometers located along the scintillometer path. The fluxes measured by the scintillometer also corresponded well to those from the line-averaged eddy covariance approach, although this agreement was greatly influenced by the choice of the zero-plane displacement length and the form of the similarity function used in the scintillometer software. A guide for choosing the appropriate similarity function for the urban roughness sublayer is proposed.