There are a few well known and even widely publicized examples of the ocean affecting hurricanes and vice versa. Tropical cyclones are, after all, nature’s Carnot engine. Just before making landfall in the record hurricane season of 2005, Katrina intensified to a category 5 hurricane while passing over a warm core ring in the northern Gulf of Mexico. On the other side of the same coin, tropical storms are frequently observed to leave an enduring cold streak upon the ocean’s surface in their wake.
Less well understood by the scientific communities interested in hurricanes—from their basic physics to improved forecasts—and the processes controlling key physical and biological variables in the upper ocean, are the details of coupled interactions between tropical cyclones and the ocean.
Does the cold wake behind one hurricane put a cap on the intensity of the next storm [Chen et al., 2017]? How does the sea spray blown off whitecaps by hurricane-force winds feed back into the latent heat fueling the growth of a storm [Zhang et al., 2017]? Can the numerical simulation and forecasting of hurricanes be improved by accounting for these and a host of other processes involved in the dynamic, two-way interaction between sea and storm [Zhao and Chan, 2017; and H. Zhang et al., 2016]? How will future changes in hurricanes and ocean warmth play off each other in the coming decades [M. Zhang, 2016]?
Recognizing that tropical cyclones are among the most destructive and costly natural hazards on Earth, and they always develop over the ocean, a new special issue of JGR: Oceans aimed to address the oceanic responses and feedbacks to tropical cyclones. Indeed, improving our understanding, simulation, and forecasts of tropical cyclones is both a scientific and societal imperative.
The special collection received more than 70 submissions from the international scientific community. Papers cover a broad range of topics including the physical mechanisms for ocean-tropical cyclone interactions, ocean-tropical cyclone interactions in the context of climate change, cutting edge techniques in data assimilation forecasting using coupled models, and other related interdisciplinary studies such as coastal environments, biochemical and geological processes.
Observations, especially those synchronized across the ocean and atmosphere, are still a major challenge for making breakthroughs on ocean-tropical cyclone interactions due to the prohibitively harsh working environment associated with tropical cyclones. Remote sensing has been a routine method to monitor storms and oceanic variability, but technological limitations inhibit some satellite sensors from fully observing the ocean and atmosphere in storm conditions.
New techniques and algorithms are continuously proposed to improve the retrieval of storm properties from Earth orbiting satellites; for example, improved estimation of wind speeds by exploiting wind-generated waves extracted from spaceborne synthetic aperture radar (SAR) [Shao et al., 2017].
Intensive and well-organized projects are usually an auspice of significant progress in the ocean-tropical cyclone studies, such as the Coupled Boundary Layer Air-Sea Transfer (CBLAST) and Impact of Typhoons on the Ocean in the Pacific (ITOP) projects. Other adaptive technologies such as the Iridium Argos and glider arrays have already made the chase more flexible and agile over the ocean.
Improvement of tropical cyclone simulation by fully coupled Earth system models remains a major challenge [Li and Sriver, 2016]. Due to the close relation between oceanic eddies and storms, eddy-resolving ocean models may be necessary for further improvement of hurricane simulation. Designing and adopting appropriate parameterizations for the sub-grid scale processes are also critical for a vivid simulation of oceanic responses to storms.
Ocean-hurricane interactions are of both scientific and socioeconomic importance, and the depth of this special section is a testament to the energy of the international scientific community addressing the challenge. Although much progress has been made, some key challenges still remain for understanding fundamental mechanisms, simulation and data assimilation technologies, and operational forecast systems.
Since the ocean and tropical cyclones have inseparable interactions over a wide range of spatial and temporal scales, it is a likely and exciting prospect that the effects of more fine-scale processes, which may be unknown so far, will be unveiled as a result of the in-depth process studies into the close coupling between hurricanes and the sea.
—Kristopher B. Karnauskas, Editor of JGR: Oceans and University of Colorado Boulder; email: [email protected], and Lei Zhou, Editor of JGR: Oceans and Shanghai Jiao Tong University