A Deep Dive into the Physics of Gap Forecasting
At Planette, we often get asked how we do what we do - what's behind our gap forecasting capabilities? Why can't regular weather models accomplish this? How is it possible to predict the evolution of the ocean? And how do conditions over the ocean relate to conditions over land?
In this post, we’re going to explore two key points that make gap forecasting possible. Note that both points are firmly grounded in physics, and confirmed through observational analysis and Earth system modeling! First, the ocean offers us a remarkably clear glimpse into the future, allowing us to forecast up to a decade ahead when primed with initial oceanic conditions. This forms the cornerstone of our gap forecasting strategy, predicting ocean evolution to understand how the rest of the Earth system will change. Secondly, the ocean and atmosphere are intricately coupled - their interconnectedness is a fundamental characteristic of the Earth system. Changes in oceanic states reverberate through the atmosphere, sculpting weather patterns and influencing terrestrial conditions. In essence, by predicting the ocean, we can grasp what to expect from the atmosphere and, consequently, conditions over land.
Let's delve deeper into each of these key points. Gap forecasting refers to predictions made between 14-day weather time horizons and 30-year climate time scales. At Planette, our focus is on forecasting critical environmental variables, including extreme weather event risks, one month to five years in advance - the exact time horizon where businesses need climate insights to adjust operations and mitigate risks.
Why Weather Forecasts Lose Their Predictive Power
At these gap timescales, weather forecasts lose their predictive power. There are several reasons for this, but the primary culprit is the chaotic nature of turbulent fluids, like the atmosphere. While the atmosphere is primarily gaseous, both the atmosphere and ocean exhibit turbulence, meaning their motion is irregular and unpredictable at small scales. Tiny discrepancies in the atmosphere’s initial conditions at a specific moment can lead to significant divergence of forecast trajectories after a certain time.
When we talk about divergent forecasts, we mean that each prediction presents a unique sequence of events. For example, one forecast might predict a rainy day followed by two sunny days, while another might predict a sunny day followed by two rainy days. This doesn't imply a complete lack of understanding about the weather, but rather an inability to predict its day-to-day evolution. For instance, a forecast for a day in May won't look like a typical day in December.
The Lyapunov Exponent
Fluid motion can be chaotic, which is evident in how the atmosphere moves. Remember the butterfly effect? In chaos theory, the beat of a butterfly’s wings in Tokyo can impact the formation of a typhoon over the West Pacific Ocean. In other words, small initial differences in weather conditions, like temperature or wind speed, rapidly evolve into significantly different forecasts. This is where the concept of the Lyapunov exponent comes in. It's a mathematical measure of how quickly forecasts diverge in chaotic systems based on tiny initial differences. The atmosphere's high Lyapunov exponent signifies that weather predictions become unreliable beyond a short period, usually a week or two.
The Ocean's Memory and Teleconnections
The ocean, however, behaves differently. Its unique characteristics lead to a smaller Lyapunov exponent. The ocean's state changes less dramatically over time. This inherent "memory" allows us to predict ocean conditions further into the future.
At Planette, we utilize a sophisticated Earth system model, a more rigorous tool compared to traditional weather models, to create our forecasts. An Earth system model incorporates mathematical representations of the atmosphere, ocean, land, and sea ice. These models are significantly more complex than numerical weather models, which only include an atmospheric model and a simplified representation of land. When we initialize Planette’s Earth system model with a specific set of initial ocean conditions, it results in forecasts that only diverge from each other after many years. There's even some ocean predictability up to 10 years into the future! Any predictions beyond weather timescales must incorporate the ocean, as it's the fluid with longer-term memory in the Earth system.
How does the ocean’s predictability connect to what happens on land, where we live? Here's where things get truly fascinating - the state of the ocean fundamentally shapes the state of the atmosphere, and by extension, the land we live on. This intricate connection is a phenomenon called atmosphere-ocean teleconnections, which might sound like science fiction, but is essentially the propagation of atmospheric waves across vast distances around the globe.
Let’s imagine an anomaly in ocean temperature, and compare it to a pebble dropped into a pond. The ripples spreading outwards are atmospheric waves carrying information about this temperature anomaly across vast distances. Think of El Niño, the cyclical warming and cooling of the eastern Pacific Ocean. Its impact on wildfires in the Pacific Northwest and monsoons in India exemplifies how these teleconnections work. The temperature anomaly in the Pacific acts like the pebble, sending ripples (atmospheric waves) across the globe, influencing weather patterns far away.
Planette's gap forecasting isn't magic, but it is the most effective method for businesses to understand and prepare for climate risks from this month up to five years from now. Planette’s gap forecasting leverages the well-understood physics of our planet's fluid systems – the atmosphere and the ocean. By understanding the ocean's predictability and its intricate connection to the atmosphere through teleconnections, we can forecast environmental conditions beyond the limitations of traditional weather models.
There's so much more to unpack regarding teleconnections, so we'll dive deeper into how atmosphere-ocean interactions illuminate the climate system next week.
