The Stratospheric Diurnal Cycle in COSMIC GPS Radio Occultation Data: Scientific Applications

The diurnal cycle throughout the stratosphere is analyzed by applying Bayesian interpolation to Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System radio occultation (RO) data and three scientific applications of the analysis are introduced. First, the migrating thermal tides are analyzed with unprecedented accuracy and precision, with an uncertainty in the analysis of the vertically propagating tides ranging from 0.1 in the lower stratosphere to 0.6 K in the upper stratosphere for an individual month of RO data and with an uncertainty in a 10-year climatological diurnal cycle a factor of 10 less. Moreover, the midlatitude trapped tide is found to be smaller than what is produced by an atmospheric model and lags the model in phase, a likely consequence of a faulty parameterization of eddy diffusivity in the upper stratosphere. Second, a clear signal of solar cycle influence on the diurnal cycle is evident in this analysis, but whether the cause is the systematic bias of ionospheric residual associated with RO retrieval or it is an actual atmospheric phenomenon is less clear. Third, RO satellites and missions that obtain inadequate coverage of the diurnal cycle will be biased by under-sampling it, whether or not subsampling weather forecasts is used to removal sampling error. The analysis of the diurnal cycle in COSMIC RO data can be used to diagnose the systematic sampling error incurred by incomplete coverage of the diurnal cycle, which is of the order of 0.2 K for a Metop-based RO climatology. Plain Language Summary The most familiar tides are those that track the Sun and Moon as sea level floods and ebbs, something that boating enthusiasts must always consider. A different kind of tide exists in the atmosphere, and these tides not only propagate horizontally as do ocean tides, but also vertically. Atmospheric tides have been extremely difficult to observe, generally because satellites have hardly ever flown in the right orbits to observe them, until the radio occultation mission Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) came to pass. If COSMIC data are analyzed using a statistical technique known for mining data for all of the information they have to offer, it becomes possible for the first time to analyze the atmospheric tides in the stratosphere, thus yielding a treasure trove of interesting science. For one, we should be able to confirm theories of how the atmospheric tides are forced. Second, we can diagnose a difficult physical problem with atmospheric models, namely how turbulence mixes air in the upper atmosphere. And third, we can also figure out what biases exist in other satellite-based data sets on temperature and pressure due to the orbits those other satellites fly in.

Automated summary

This study analyzes the diurnal cycle in the stratosphere using Bayesian interpolation applied to COSMIC Global Positioning System radio occultation data. Three scientific applications of the analysis are introduced, including analysis of migrating thermal tides, detection of solar cycle influence, and diagnosis of sampling error. The analysis provides unprecedented accuracy and precision in analyzing the tides, reveals deviations from atmospheric models, and highlights the importance of sufficient coverage in satellite-based data sets.