GD6: Urban climatology studies I : temperate and cold climate cities
60 year variability in meteorological and environmental characteristics of the atmosphere in Moscow megalopolis
1Faculty of Geography of Moscow State University Russian Federation; 2A. M. Obukhov Institute of Atmospheric Physics RAS Moscow Russian Federation
We analyze the results of meteorological and air quality measurements over the 60-year period (1954–2013) at the Meteorological Observatory of Lomonosov Moscow State University (MSU MO) located in the megalopolis with more than 12 million population. A complex program of meteorological and radiadive observations as well as aerosol, air and precipitation quality measurements has been in operation there according to the guidelines and the standards established by WMO and Russian Hydromet Service.
The significant positive temperature trend (+0,041С/year over 1954–2013) was obtained, which has been increased up to +0,067С/year for 1976–2012. This trend is slightly larger than the rate of temperature increase in the Central Federal District (CFD) (0,059CS / year) and over the whole Russia (0,043C / year). In addition, a long-period variability in net radiation and particular, in long-wave net radiation over 1954-2013 demonstrated a dramatic increase in the last decades. We show the possible mechanism of larger temperature increase in Moscow compared with that in the Central Federal District which can be connected with the greenhouse effect of the urban atmosphere. This mechanism is in accordance with the observed tendency of increasing downwelling long-wave radiation during the last decades.
The long-term measurements of shortwave irradiance, natural illuminance, PAR and UV radiation demonstrate a pronounced decrease in the 1970s and the increase during the last decades due to changes in global scale circulation. The interannual changes in biologically active UV radiation are characterized, in addition, by the large influence of decreasing total ozone content since the end of 1980s. In 2011, for example, we observed the absolute maximum level in biologically active UV radiation (+11%) and especially high UV-B radiation in spring 2011, when the Arctic ozone hole spread over the Moscow district. We propose a method for evaluating the optimum UV level for human health. According to the estimates, in Moscow the UV optimum is observed from the middle of March to the end of April, and from the end of September to the middle October.
The analysis of chemical composition of precipitation and pH since 1980, shows a significant seasonal and inter-annual variability with large frequency of acid precipitation in 1980-1990s, its significant decline in 1999- 2004, and a noticeable increase - since 2005. These variations are accompanied by the change in chemical composition from sulphate to chloride dominating ions. The analysis has revealed the effects of local pollution of Moscow megalopolis and the significant role of de-icing salts in increasing the chloride ions concentration and the acidity of the precipitation.
Aerosol studies since 1955 demonstrate a pronounced negative trend in aerosol optical thickness (AOT) from 1990s. According to the AERONET measurements since 2001 in MSU MO the negative AOT trend is observed in the last decade as well. The trend is characterized by the substantial decrease in aerosol fine mode fraction. Long-term AERONET collocated measurements at the MSU MO and at the Zvenigorod Scientific Station of the IAP RAS, which is located in background conditions, have revealed the Moscow aerosol pollution effect of about 0.02 for AOT at 500 nm with the increase of up to 0.04 in winter time. According to RT modelling we show the consequences of this effect on solar radiation in different spectral regions. Column aerosol content as well as the surface concentrations of aerosol particles smaller than 2.5 microns (PM2.5) demonstrate a summer maximum due to the active processes of second aerosol generation. The analysis of daily average PM2.5 in Moscow shows that the excess of maximum allowable concentration was detected 4 times in 2011, 10 times - in 2012 and 31 times - in 2013. In comparison with other megalopolis areas of Eurasia and America a moderate level of gaseous air pollution in Moscow is observed. The worst air pollution provides by nitrogen oxides, which content is comparable to that in cities of the industrialized countries.
The work was partially supported by the grants RFBR #13-05-00956, and RFBR #15-05-03612.
The influence of wind advection on an urban heat island using the HiTemp network of sensors
1University of Birmingham, United Kingdom; 2Public Health England
A series of recent projects have examined the exact nature of the UHI in Birmingham using a variety of approaches. Whilst the magnitude and spatial aspect of the UHI has been quantified (approx. 6°C), there has been little notion to the dynamic nature of the UHI. It has been hypothesised through modelling that wind travelling across urban areas will transport heat downwind (Heaviside et al. 2014). A network of automatic weather stations (HiTemp) has been installed across Birmingham that commenced observations in January 2013. In conjunction with existing Met Office weather stations a total of 29 station datasets are available across a broad range of land use types for a period of 20 months. This data (filtered for night-time, low cloud cover and low wind speed) is used in this study to analyse the effects of wind advection on the spatial UHI pattern. Preliminary results using station pairs across the city show that mean temperatures on the downwind side to be up to 0.8°C warmer. Subsequent spatial interpolations (kriging) of the whole dataset shows a distinct UHI pattern linked directly to landuse. Using a methodology adapted from Heaviside et al. (2014), who decomposed a modelled UHI field into local and advected warming, a clear secondary signature is found whereby the downwind side of Birmingham is warmer than the mean and upwind cooler. The overall aim is to quantify heat advection contribution for different windspeeds and at different scales, i.e. neighbourhood to city.
Heaviside, C., Cai, X.M. and Vardoulakis, S. 2014. The effects of horizontal advection on the urban heat island in Birmingham and the West Midlands, United Kingdom during a heatwave. Q. J. R. Meteorol. Soc.
Urban heat island and inertial effects : analyse from field data to spatial analysis
1L’UNAM, L’UNAM, CNRS, LHEEA/IRSTV, France; 2L’UNAM, ENSA Nantes, CERMA/IRSTV , ADEME, France; 3L’UNAM, EC Nantes, IRSTV, France; 4L’UNAM, EC Nantes, LHEEA/IRSTV, France; 5L’UNAM, ENSA Nantes, CERMA/IRSTV, France
The maximum urban heat island often occurs few hours after sunset. This may be explained by the thermal inertia of the urban canopy which is often much higher than that of rural sites. The cooling rate is an indicator of urban thermal inertia computed from on-site measurement but is mainly used to dissociate thermal behaviour difference between urban and rural sites. This paper proposes a new method to better dissociate the thermal inertia properties between urban sites from air temperature measurement.
The first part of our paper presents the method of computation, its results under different meteorological conditions which are then compared to the results obtained from the cooling rate calculation. Our method is based on the phase shift computation of temperature diurnal cycles between several urban stations and a reference rural station. Fifteen minutes data collected during four years from ten temperature stations are used. The stations network is located in Nantes, the 6th largest city of France with a total population in its metropolitan area of 590 000 inhabitants. The climate is western European oceanic and is characterized by a relatively mild summer. The phase shift was first calculated considering different meteorological situations. The results show that the sun radiation amount affects directly the phase shift difference values. The wind speed and direction also play a role on the results even if the influence is lower. In a second step, our indicator is compared to the average cooling rate after sunset, an usual indicator of thermal inertia. The results show that the phase shift better dissociates the stations than the cooling rate regarding to their thermal inertia properties.
In a second step, the phase shift results are analysed in relation with geographical indicators (facade density, vegetation density, etc.) calculated from BDTopo®. The reference surface for the spatial analysis is defined by concentric circles of different sizes around each measurement station. Results of linear regressions show that our new thermal inertia indicator is well correlated to geographical parameters (R² > 0,5 - e.g. for aspect ratio). These results can be used to identify high thermal inertia zones, where the urban heat island is expected to occur during night-time.