On the use of Cell Phones data to characterize the Atmosphere in Urban Areas

The aim of the present contribution is to assess the validity of the meteorological data recorded by cell phones in urban areas, a necessary step previous to the use of such data. In particular, the focus is on hourly values of pressure and temperature, because this is the time scale most relevant for many applications, from data assimilation in NWP models, to thermal comfort studies in urban areas, for example. As test cases, the cities of Madrid and New York are considered for the month of September 2015. These two cities are very different in terms of structure and geographical setting, so that from the comparison conclusions can be derived about the geographical variability of the quality of cell phone data. Results are analysed at the scale of the whole city, and at the scale of one kilometer, considering only the cell phone data close to the measurement stations. Results indicate that cell phone data can give a reliable measure of the pressure at the scale of the city, with a bias (negative for New York and positive for Madrid) that can be easily corrected. However, at smaller scale, the spatial variability of the pressure from cell phone data is higher than the one measured by the fixed stations. For temperature, the general tendency of cell phone data is to underestimate the daily variation. Neverthless in the case of Madrid it is possible to find a least square correction able to reproduce relatively well the time evolution of air temperature at the scale of the whole city. This is not possible for New York. Finally, cell phone data are not able yet to reproduce the small scale spatial variations of temperature observed in cities.  Factors that can lead to an improvement in this technique are a denser set of data, allowing a more sophisticated stiatistical treatment, and a better determination of the position of the cell phone, including height above ground (for pressure), and a separation between indoor and outdoor.

Aknowledgement.

Pressure net data were made available cortesy of the Sunshine Company. Weather Signal data cortesy of Weather Signal.com