SIMONe systems

Specular meteor radars (SMRs) are reliable and powerful tools to investigate mesosphere and lower thermosphere (MLT) dynamics. Reliable, because they operate 24/7 under any sort of weather conditions. Powerful, because they can provide accurate horizontal winds with a reasonable time resolution (~ 1 hour) for altitudes between 80 and 100 km. Ideally, one would like to know the wind vector at any point in space and time, i.e., to determine the wind fields. However, in order to do the latter, the geometry of conventional SMR observations has to be modified and upgraded to a multistatic configuration.

With this idea in mind, the IAP has recently developed the MMARIA (Multistatic Multi-frequency Agile Radar for Investigations of the Atmosphere) concept. MMARIA represents an extension of traditional meteor radar systems in which several spatially separated receivers are added to existing transmitting stations, and/or several spatially separated transmitters are added to existing interferometric receiving stations (Stober and Chau, 2015, Chau et al., 2017). Besides detecting between half and one order of magnitude more meteors, the MMARIA systems are able to observe almost the same detection volume from different viewing angles, which is essential to determine the horizontal wind fields (see figure 1).

The MMARIA concept can be materialized with both pulsed and coded continuous wave (CW) meteor radar systems. The latter approach is named SIMONe (Spread spectrum Interferometric multistatic Meteor radar Observing Network), and it has been proven to provide MLT winds with unprecedented time resolution (Vierinen et al., 2019), and to be significantly more cost-effective and easier to install than conventional SMRs. Furthermore, unlike other instrumentation (e.g., optical measurements, lidars), SMR networks like SIMONe are perfectly suited for continuous, long-term records.

SIMONe systems have been developed by IAP, in collaboration with MIT Haystack (US) and the Arctic University of Norway (Chau et al., 2019). A description of the operational SIMONe systems can be found in Chau et al., (2021). Thanks to the large amount of meteors that these systems can detect (see figure 2 for examples of daily meteor counts), novel approaches such as the wind field correlation function inversion (WCFI) technique (Vierinen et al., 2019) can be implemented to, for example, obtain horizontal correlations of the vertical vorticity and horizontal divergence. Recently, the latter two parameters have been investigated for the first time at MLT altitudes using SIMONe observations (e.g., Poblet et al., 2022). Studies like this are crucial, since they can shed light on the type of physical mechanism driving the MLT dynamics at horizontal scales of approximately 50 to 450 km, i.e., mesoscales.

Currently, the IAP operates five different multistatic SMR networks. Two in Europe, MMARIA Norway (69°N) and MMARIA Germany (53°N), and three in South America, SIMONe Piura (5°S) and SIMONe Jicamarca (12°S), in Peru, and SIMONe Argentina (49°S), in southern Patagonia.