17 August 2022 | Category: CloudRoots Amazonia

Where and how is the cloud?

By Jordi Vila

Professor Meteorology and Air Quality at Wageningen Universi...

Will it rain? When? How deep is the cloud? Will it grow deeper? How much? A lot of questions without answers. But the soundings observing meteorological variables can provide us some quantification. So far what we have experienced during the CloudRoots campaign at the Amazonia are clear mornings. After lunch, more precisely, after midday, there are some white puffs floating in the air. In some days they develop very fast and produce short and intense showers. How can we know more about their development, and about their conditions?

To do this, during the entire CloudRoots Amazonia, we have set an intense campaign of radio soundings to measure the vertical profiles of temperature, relative humidity, wind speed and wind direction. This is the story.

From sunrise to sunset

A team composed of seven Brazilians scientists (5 of them MSc or PhDs) from INPA is following a strict schedule. From sunrise (6 AM) to sunset (6 PM), they are launching every three hours a sounding that sends via radio the information of temperature, relative humidity, wind speed and direction. Before the scheduled time, the team inflate the balloon with helium, synchronized to the radio and off we go (photos 1 and 2). The balloon ascends rapidly with a speed of more than 3 m/s (1000 m in more or less 5 minutes), and it is sending an observation of temperature, relative humidity, wind speed and wind direction every 5 meters. A lot of detail, but we need it. What do we do with it?

Picture 1: Sounding ready to be launched.

Picture 2: Sounding launched at 6 AM local time with the moon as witness.

The figure below shows the information that we are getting by radio almost immediately. On the left, the temperature decreases with height as we expect. On the right, the relative humidity increases with height until 1500 m, almost reaching 80%. This height marks the cloud base. In very short, parcels of air full of moisture are moving upwards by turbulent motions. At the height of 1500 m, the temperature has dropped to 20 C, and here moisture condensates.

This might lead to the formation of clouds. If condensation occurs, energy is released which enables the air parcel to keep of ascending. Under the optimal condition for the cloud formation, the cloud droplets grow enough, producing rain. During CloudRoots Amazonia we aim at investigating how the rainforest is regulating the ascension of moisture and particles and the amount of evaporation driven by plants during the photosynthesis.

Figure 1: Profiles of temperature and relative humidity observed August 10th at 15 local time.

Fly over the Amazonia

But this is not all. After the sounding is ready, we sent all the data to the European Centre for Medium-Range Weather Forecasts (ECMWF) in Reading, United Kingdom. This is one of the best weather forecasting institutes in the world. Tropical regions like the Amazonia are difficult to be forecast since they develop clouds and showers very rapidly and at very localized regions. By including the information provided by the sounding observations, we hope to improve our scores in forecasting the weather in the Amazonia. Let’s see if it is true.

Enough about the weather. CloudRoots Amazonia strives to have a proper balance between land processes, weather and atmospheric composition. Let’s talk about the latter. In the very last minute, we are trying to arrange a plane to fly over the Amazonia to observe the profiles of carbon dioxide and monoxide, and methane. It is uncertain, but we do our best. Stay tuned!

By Jordi Vila

Professor Meteorology and Air Quality at Wageningen University & Research

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