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The results of numerical simulations of a positive streamer development in air in a weak and uniform electric field are presented. Streamer dynamics is considered in an electrode gap of 33 mm in length and the configuration was 'protrusion on a plate-plate'. This particular configuration was chosen in order to perform direct comparison between simulated results and experimental data. The electrostatic field in such a system decreases rapidly with increase of the distance from the protrusion (anode) and the region with a weak and uniform background field covers ∼30 mm of the gap. The parameters of the propagating streamer are studied at six different values of the background field strength: 0.24; 0.30; 0.345; 0.37; 0.43 and 0.50 MV m −1 . Stable streamer development (with constant velocity) takes place in a field of 0.5 MV m −1 (the stability field) but the streamer is able to cross the gap in a background field of 0.3 MV m −1 . These values are in excellent agreement with experimental data. During the stable streamer propagation, the electron density and plasma conductivity in the discharge channel and the electric field at its front remain constant. In a background field lower than 0.5 MV m −1 , the discharge front velocity and the electric field at the front decrease linearly with an increase of streamer length. The discharge propagation in the stability field is associated with an increase of electrostatic energy at the streamer front but it decreases if the streamer develops in a weaker electric field. This behaviour is accompanied by a constant Joule dissipation at 0.5 MV m −1 and decreasing energy losses at the streamer front in a weaker background electric field.

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General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract. A measurement of the positive streamer charge has been performed at atmospheric conditions in a quasi-uniform electric field where the discharge was electrically triggered. By applying a square impulse voltage to the trigger electrode, which was close to, but electrically isolated from, the anode, a positive streamer discharge with one discharge event was produced. The voltage, current and luminosity associated with the streamer discharge were measured simultaneously. By placing a photographic film at the cathode, the number of individual streamers hitting the cathode was estimated within one discharge event.The amount of net charges in streamer discharges has been evaluated for different background electric fields. From the results, it has been deduced that each individual streamer channel contains a charge represented by an excess of 1.1-2.0 × 10 11 positive ions m −1 . The lower value corresponds to a background field of 400 kV m −1 and the higher one to 600 kV m −1 . The streamer has also been simulated using a simplified streamer model. The results of the measurement and the calculation are compared and discussed.