Climate Monitoring of Atmospheric Heat Content and Heat Exchange with the Oceans: A New Key Role for Radio Occultation
Presenter:
Gottfried Kirchengast
Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Graz, Austria
Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria
Talk
Radio occultation (RO) based on GNSS signals has meanwhile delivered a novel record of global atmospheric data over almost two decades and will continue so over the next decades. RO reliably tracks the fundamental thermodynamic state of the atmosphere (density, pressure, temperature, tropospheric water vapor) and its changes, including in atmospheric heat content (AHC). Due to its nature as an SI-traceable global refractometer from space, RO performs this by monitoring the troposphere and stratosphere with a unique combination of high accuracy, resolution, long-term stability, and nearly all-weather global coverage. Further high-quality records since the 1990s, from selected atmospheric radiosonde (RS), sea surface temperature (SST), and ocean heat content (OHC) datasets, can valuably complement RO as do re-analyses (RA) of increasing quality such as the recent European Reanalysis ERA5.
Building on these capabilities, we computed a latitude-resolved monthly-mean AHC record from WEGC-processed RO over 2001-2018, complemented it from 1993 onwards by RS, RA, SST, and OHC records, and investigated decadal trends and inter-annual variations in AHC and atmosphere-ocean heat (ex)changes over the last 25 years. Together with total AHC we analyzed components of AHC, with focus on sensible heat (essentially composed of internal heat energy and gravity potential energy) and latent heat (essentially heat of condensation stored in water vapor). In doing this, we first developed an understanding of the level of long-term stability, homogeneity, and consistency of the data records, and related limitations, after which we analyzed total AHC changes, AHC component changes, and heat exchanges along different atmospheric and oceanic domain separations.
We present results with focus on the tropics, in global context, where we diagnosed heat energy redistributions among main atmospheric layers (lower troposphere, upper troposphere, lower stratosphere) as well as across the sea surface with upper ocean layers (mixed 0-100m, transition 100-300m, deep-upper 400-700m). We find a consistent physical picture of climate change-induced heat increase in the atmosphere and mixed uppermost ocean, jointly with inter-annual imprints of El Niño/La Niña and other variability modes, over 1993-2018 and 2001-2018, respectively. The results indicate a global AHC trend substantially larger over 2001-2018 than the IPCC Assessment Report AR5 estimates for 1979-2010; we discuss this difference and its implications. Overall the results testify to the exceptional utility of the records used, and specifically to RO playing the key role in providing AHC as a highly reliable and promising new atmospheric climate monitoring metric.
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