Hello world, from OTREC

Organization of Tropical East Pacific Convection (OTREC) is a collaborative scientific project, funded by the US National Science Foundation, to study the weather in the tropical eastern Pacific and western Caribbean. This blog will document OTREC informally, as scientists in the field report on their experiences as well as the observations made.

The area of study was chosen because of its unique climate, strongly influenced by a very strong sea surface temperature gradient. The coldest temperatures in the tropics are found here on the equator, while very warm temperatures are found nearby to the north. These strong contrasts in sea surface temperature have influences on the convection – the tall cumulus clouds that produce heavy tropical rain – that we still don’t understand very well. The best way to improve that understanding is to go there and directly observe what is going on.

The field phase of OTREC will begin on August 5 and continue until September 30, 2019. Dozens of scientists and students from the USA, together with colleagues from several nearby Latin American countries, will be stationed in Costa Rica during this time. We will gather data from the NCAR/NSF Gulfstream V aircraft. From the plane we will, over the time of the experiment, deploy 600 dropsondes (instruments that measure temperature, humidity, wind, etc., all the way from the plane to the ocean; basically these are similar to weather balloons, but they fall down with a parachute instead of rising up with a balloon) and NCAR's downward-pointing W-band radar, which can see the rain-bearing clouds. Additional radiosondes (normal weather balloons) will be launched from the ground from locations in Costa Rica and Colombia.

  

The core group of investigators in OTREC consists of scientists from Harvard University, University of Wisconsin, National Oceanic and Atmospheric Administration, Colorado State University, University of Washington, Columbia University and New Mexico Tech. The international collaborators are from Mexico, Costa Rica, and Colombia. The project is being led by physicists Zeljka Fuchs-Stone and David J. Raymond from New Mexico Tech.

Sea surface temperature map (scale at right, degrees C) in the OTREC region of study. Boxes show the planned flight areas.

Planned flight patterns for the boxes in the preceding image.

OTREC motivation

The weather forecasts that we depend on for many aspects of modern life are made possible by computer models that simulate the behavior of the atmosphere, using the laws of physics in an approximate form. The models are imperfect, but continuously improving. One of the reasons for this improvement is the increase in the power of computers, which allows the models to approximate the laws of physics more accurately. Another is better understanding of the physics in order to allow better approximations even with the same computers. But observations are critical at every stage. We need observations to know what the weather is now, in order to give the forecasts a starting point. Also, we need observations to evaluate the models, to see what they are doing wrong. Carefully designed observations can allow us to improve our understanding of the underlying physics so that we can figure out how to make the models better.

Weather forecasts in the deep tropics are particularly challenging. Most of the tropics is covered by ocean, so that in situ observations are sparse. Also, weather in the tropics is strongly controlled by deep convective cloud systems – complexes of thunderstorms whose clouds reach high up into the atmosphere, that produce heavy rain, that steer the winds on large scales, and that sometimes organize into hurricanes. Our understanding of these deep convective systems remains quite incomplete despite decades of study, and models still struggle to represent them well. Basic questions are: why does the convection develop at particular places and times and not others? Why does it sometimes develop and sometimes not, even when conditions seem ripe? OTREC will try to answer these and other questions. In the coming weeks, we will explain in more detail what we are doing and what we find.

Zeljka Fuchs-Stone and Adam Sobel