Weather surveillance for the space center

30 mars 2019 0 Par Peebee

The climate in Guyana

Due to its geographical location, weather in Guyana is mainly dictated by the motion of the Inter-tropical Convergence Zone (ITCZ).

This area, located around the equator, is the convergence between Northeast and Southeast convective winds, leading to quickly expending convective clouds (Cumulonimbus).

The ITCZ shifts North and South of the equator during the year, influencing Guyana’s weather.

From December to January : Rainy
From February to April : « Little » dry season
From May to July : Rain season
From August to November : Dry season

Within the ITCZ the convective clouds can develop up to 14km high in less than 45 minutes, but are usually isolated. They can be detected with Doppler weather-radars and the main risks for rockets around CBs are lightning strikes and icing.

A complete surveillance system

The space center has its own weather station monitoring weather on the base and its surroundings.

To perform prediction, the station has access to a whole array of equipments. Among them we find two radars : RODIN and ROMUALD. The first one is the oldest and can be found on the station building itself while the second one is situated at the top of the « montagne des Pères ». Both of them allow to detect rainfalls and thunders.

RODIN, one of the two radars of the station

Other information are provided using satellite coverage, with for instance an American geostationary satellite (these information are mainly views of the sky with varying wave length).

The station does have an hangar to prepare probe balloons too. They are sent right before launch to provide up to date information on the atmosphere at different altitudes between the ground and 30km. They send it with an ascension speed around 5m/s to compromise speed and resolution (the slower the balloon is, higher is the number of measures they can gather, but longer is the time before they get all intel).

Morever, numerous other devices are scattered upon various measure points on the base and its surroundings. They provide intel on wind, temperature, pressure, rainfalls. There are several « moulins à champs » that can predict lightning impacts by measuring variations in the vertical component of the electrostatic field (these sensors are triggered by rainfalls too… which is not an intented feature).
Finally, the station use several tools from Meteo France, especially model for simulations. They mainly use two model. « Centre européen » which is an earth wide model with an 10km mesh* approximately and « Arome Tropique », designed for climate like in Guyane and has an 2.5km mesh approximately.

Tools from Meteo France are used to perform simulations

*It define the size of the grid on wich the simulation value. The smaller it is, better is the precision on a geographical level.

Role of the station in the base

Weather is a critical factor during the whole launch campaign, especially during the launch phase.

4 meteorologists from Meteo France (including today’s lecturer) and 3 weather-radar operators monitor real-time weather and prepare forecast for all activities on the base.

During the final chronology, 2 met-specialists and 2 radar operators are tasked to monitor the critical parameters that could prevent the launch:

Surface wind velocity & direction (to prevent contamination of nearby areas in case of explosion)
No lightning strikes within 10km of the launch pad
No Cumulonimbus within 20km around the launchpad (source of electrostatic discharges, even in altitude)

If criteria are not met, the launch can be delayed.

A few minutes before the launch, the team move in a secure bunker for the rest of the operations.