Tropical mid-tropospheric CO_2 variability driven by the Madden–Julian oscillation

Carbon dioxide (CO_2) is the most important anthropogenic greenhouse gas in the present-day climate. Most of the community focuses on its long-term (decadal to centennial) behaviors that are relevant to climate change, but there are relatively few discussions of its higher-frequency forms of variability, and none regarding its subseasonal distribution. In this work, we report a large-scale intraseasonal variation in the Atmospheric Infrared Sounder CO_2 data in the global tropical region associated with the Madden–Julian oscillation (MJO). The peak-to-peak amplitude of the composite MJO modulation is ~1 ppmv, with a standard error of the composite mean < 0.1 ppmv. The correlation structure between CO2 and rainfall and vertical velocity indicate positive (negative) anomalies in CO_2 arise due to upward (downward) large-scale vertical motions in the lower troposphere associated with the MJO. These findings can help elucidate how faster processes can organize, transport, and mix CO_2 and provide a robustness test for coupled carbon–climate models

Atmospheric hydroxyl radical (OH) abundances from ground-based ultraviolet solar spectra: an improved retrieval method

The Fourier Transform Ultraviolet Spectrometer (FTUVS) instrument has recorded a long-term data record of the atmospheric column abundance of the hydroxyl radical (OH) using the technique of high resolution solar absorption spectroscopy. We report new efforts in improving the precision of the OH measurements in order to better model the diurnal, seasonal, and interannual variability of odd hydrogen (HOx) chemistry in the stratosphere, which, in turn, will improve our understanding of ozone chemistry and its long-term changes. Until the present, the retrieval method has used a single strong OH absorption line P1(1) in the near-ultraviolet at 32,341 cm−1. We describe a new method that uses an average based on spectral fits to multiple lines weighted by line strength and fitting precision. We have also made a number of improvements in the ability to fit a model to the spectral feature, which substantially reduces the scatter in the measurements of OH abundances

Short-period solar cycle signals in the ionosphere observed by FORMOSAT-3/COSMIC

We analyze 2 years of the FORMOSAT-3/COSMIC GPS radio occultation data to study the response of the Earth's ionosphere to the solar rotation (27-day) induced solar flux variations. Here we report electron density variations in the ionosphere (∼100–500 km) associated with the 27-day solar cycle. The peak-to-peak variation in electron density at low latitudes in the F2 region is about ∼10^4–10^5 electrons cm^(−3) or 20–40%, and can be as high as 60% depending on altitude, latitude, and season. The half and double periods of the 27-day are also observed at an amplitude comparable to that of the 27-day. The results place useful constraints for modeling chemical and dynamical processes in the ionosphere

Resolving the model-observation discrepancy in the mesospheric and stratospheric HO_x chemistry

We examine the middle atmospheric odd-hydrogen (HO_x) chemistry by comparing the Aura Microwave Limb Sounder (MLS) OH and HO_2 measurements with a photochemical model simulation. The model underestimates mesospheric OH and HO_2 concentrations if the standard chemical kinetic rates are used, whether the model H_2O and O_3 are constrained with observations or not. To resolve the discrepancies, we adjust the kinetic rate coefficients of three key reactions (O + OH → O_2 + H, OH + HO_2 → H_2O + O_2, and H + O_2 + M → HO_2 + M) and the O2photo absorption cross section at Lyman-α (121.57 nm) using the Bayesian optimal estimation. A much better model-observation agreement can be achieved if the kinetic rate coefficients for H + O_2 + M → HO_2 + M is increased by 134–310%, and the O_2 photo absorption cross section at Lyman-α is reduced by 33–54%, while the kinetic rate coefficients for O + OH → O_2 + H and OH + HO_2 → H_2O + O_2 remain consistent with the current laboratory values. The kinetic rate coefficient for H + O_2 + M → HO_2 + M requires a very large adjustment beyond the uncertainty limits recommended in the NASA Data Evaluation, suggesting the need for future laboratory measurements. An alternative explanation is that the radiative association reaction, H + O_2 → HO_2 + hν, plays a significant role, which has never been measured. Our results demonstrate that high quality satellite observations can be used to constrain photochemical parameters and help improve our understanding of atmospheric chemistry

A link between tropical intraseasonal variability and Arctic stratospheric ozone

Previous studies using satellite measurements showed evidence that subtropical upper troposphere/lower stratosphere ozone (O_3) can be modulated by tropical intraseasonal variability, the most dominant form of which is the Madden Julian Oscillation (MJO) with a period of 30–60 days. Here we further study the MJO modulation in the upper troposphere/lower stratosphere O_3 over the northern extratropics and the Arctic. Significant MJO-related O_3 signals (13–20 Dobson units) are found over the northern extratropics (north of 30°N). The O_3 anomalies change their magnitude and patterns depending on the phase of the MJO. Over the Arctic, the MJO-related O_3 anomalies are dominated by a wave number 2 structure and are anticorrelated with the geopotential height (GPH) anomalies at 250 hPa. The latter is similar to the findings in the previous studies over subtropics and indicates that the Arctic upper troposphere/lower stratosphere O_3 anomalies are associated with dynamical motions near the tropopause. The teleconnection from the tropics to the Arctic is likely through propagation of planetary waves generated by the equatorial heating that affects the tropopause height and O_3 at high latitudes