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Changes in daily scale thermal inertia of the ocean surface
Changes in daily scale thermal inertia of the ocean surface
During my master's years, my main interest was the thermal state of the ocean surface. I specifically have focused on the thermal inertia of the ocean surface, which has a huge impact on marine ecosystems. The main approaches to analyzing satellite observations and reanalysis data were statistical methods. Here, you can find the changes in the thermal memory of the ocean surface and its causes. You can check the details here (Lee et al., 2025).
Fig 1. (a) Mean daily surface thermal memory for the past 40 years, and (b) Trend surface thermal memory for the past 40 years range from 1982 to 2021. The dot indicates basins that have a statistically significant trend.
Fig 1 shows the mean and the trend in thermal inertia of the ocean surface, evaluated using daily-resolution satellite-based sea surface temperature (SST) observation data.
As seen in Fig 1b, the thermal memory of the ocean surface has increased over most of the basin in the past few decades, with an average increase of about 10 days in the mid-latitudes. This increasing pattern cannot be ignored based on the fact that the thermal memory in 2021 is greater than that of 1982 by roughly 100 % globally.
Fig 2. Power spectral density (PSD) of the sea surface temperature anomalies for five regions, indicated by white boxes in Fig. 1. The averaged PSD for the first and last five years of the analyzed period is shown by black and red lines, respectively, with shading representing one standard deviation.
Fig 3. a-b. The linear trend of the summertime and wintertime mixed layer depth spanning from 1970 to 2018 (Sallee et al., 2021). c-d. The linear trend in total surface lambda_a, and in lambda_o associated with the oceanic processes from 1982 to 2021. Dotted regions in both c and d have statistically significant trends at a 95 % confidence level.
To reveal the mechanism behind the increase, power spectral density (PSD) of the SSTa in the two different time domains, represented in Fig 2 and the changes in the mixed layer and negative heat flux feedback rate, depicted in Fig 3, are evaluated.
The later five-year (2017-2021) average PSD in the high-frequency domain has a lower magnitude than the first five years (1982-1986) in Fig. 2. This suggests that the variation of the fast-decaying anomalies has decreased over the analysis period. This alteration is attributed to the deepened mixed layer and the decreased negative heat flux feedback rate in the upper ocean, as shown in Fig. 3.
You can check the detailed information here
Beyond this study:
Make a connection between physical phenomena in the upper ocean to changes in the decreasing trend of the negative heat flux feedback rate. This analysis will consist of interpreting the inverse cascade process and the role of mixing by analyzing high spatial and temporal resolution in situ observations and/or by employing ocean model experiments.
How does the change in the upper ocean's thermal state affect the ocean's ability to absorb and store excess atmospheric heat in a warming climate? This research focuses on the physics of the atmosphere-ocean interface at multiple scales, both temporal and spatial.
If you have any questions or advice, please contact me!
Chaehyeong.Lee [at] colorado.edu
Banner picture source: https://www.news.uliege.be/cms/c_9681629/en/the-ocean-is-losing-its-breath
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