The adsorption of C12E8 onto a clean air-water interface is studied by using a video-enhanced pendant bubble tensiometry. The controlling mechanism for mass transfer changes as a function of bulk concentration; it shifts from diffusion control at dilute concentration to mixed diffusion-kinetic control at more elevated bulk concentration. The adsorption of C 12E8 is found to be anticooperative from the equilibrium surface tension data compared with the prediction of the (generalized) Frumkin model. Relaxation profiles of surface tension for C12E8 molecules absorbing onto a freshly created air-water interface for 21 different bulk concentrations are obtained. Comparison is made for the entire relaxation period of the tension data and the model predictions. Values of the diffusion coefficient and the adsorption/ desorption rate constants of C 12E8 are calculated from these dynamic surface tension profiles.

This paper demonstrates the significance of ion-neutral coupling to ionospheric data assimilation for ionospheric specification and forecast. Ensemble Kalman Filter (EnKF) is used to assimilate synthetic electron density profiles sampled according to the Formosa Satellite 3/Constellation Observing System for Meteorology, Ionosphere, and Climate into the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The combination of the EnKF and first-principles TIEGCM allows a self-consistent treatment of thermosphere and ionosphere coupling in the data assimilation and forecast. Because thermospheric variables affect ionospheric electron densities, different combinations of an observed ionospheric state variable (electron density), and unobserved ionospheric and thermospheric state variables (atomic oxygen ion density, neutral temperature, winds, and composition) are included as part of the EnKF state vector in experiments. In the EnKF, the unobserved state variables are estimated and made dynamically and chemically consistent with the observed state variable, thus improving the performance of the data assimilation system. The impact on ensemble forecast is further examined by initializing the TIEGCM with the assimilation analysis. The main findings are the following: (1) by incorporating ion-neutral coupling into the EnKF, the ionospheric electron density analysis, and forecast can be considerably improved. (2) Thermospheric composition is the most significant state variable that affects ionospheric analysis and forecast. (3) Thermospheric variables have a much longer impact on ionospheric forecast (>24 h) than ionospheric variables (2 to 3 h). (4) In the TIEGCM, the effect of assimilating electron densities is not completely transmitted to the forecast step unless the densities of ion species are estimated.

The adsorption of C10E8 onto a clean air−water interface and the desorption out of an overcrowded interface due to a sudden shrinkage of a pendant bubble in a quiescent surfactant solution are studied. Video-enhanced pendant bubble tensiometry is employed for the measurement of the relaxation in surface tension. Relaxation profiles of surface tension for C10E8 molecules absorbing onto a freshly created air−water interface and desorbing out of a compressed air−water interface are obtained. The adsorption of C10E8 is found to be anticooperative from the equilibrium surface tension data compared with the prediction of the Frumkin model. The controlling mechanism of the adsorption process changes as a function of bulk concentration; it shifts from diffusion control at dilute concentration to mixed diffusive-kinetic control at more elevated bulk concentration. It is also confirmed that the desorption of C10E8 out of a compressed interface is a mixed diffusive-kinetic controlled process. Comparison is made for the entire relaxation period of the tension data and the model predictions. Values of the diffusivity and the adsorption/desorption rate constants of C10E8 are calculated from these dynamic surface tension profiles. The values of the kinetic rate constants obtained from the desorption experiment are the same as that obtained from the clean adsorption experiment.

The adsorption of C12E4 onto a fresh air-water interface was investigated by using video-enhanced pendant bubble tensiometry. From the comparison between the equilibrium surface tension data and the theoretical relaxation profiles predicted by the Frumkin adsorption isotherm, the adsorption process was found to be anticooperative. Dynamic surface tension data for C12E4 molecules absorbing onto a freshly created air-water interface for different bulk concentrations were used for the determination of the controlling mechanism and the evaluation of diffusivity. Comparison was made for the entire relaxation period of the surface tension data and the model predictions. It is concluded that the adsorption process is of diffusion control and the diffusion coefficient is 6.4 × 10 -6 cm 2 /s. The lower limit of the adsorption rate constant of C12E4 were obtained from the theoretical simulation. Besides, the pendant bubble, at which the interface had reached the equilibrium state, was expanded rapidly and a relationship between surface tension (γ) and surface area (A) was obtained. A curve relating γ and relative surface concentration Γ/Γref was obtained from the γ-A data and then used to examine the adsorption isotherm utilized in this study.

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The main purpose of this paper is to investigate the effects of rapid assimilation‐forecast cycling on the performance of ionospheric data assimilation during geomagnetic storm conditions. An ensemble Kalman filter software developed by the National Center for Atmospheric Research (NCAR), called Data Assimilation Research Testbed, is applied to assimilate ground‐based GPS total electron content (TEC) observations into a theoretical numerical model of the thermosphere and ionosphere (NCAR thermosphere‐ionosphere‐electrodynamics general circulation model) during the 26 September 2011 geomagnetic storm period. Effects of various assimilation‐forecast cycle lengths: 60, 30, and 10 min on the ionospheric forecast are examined by using the global root‐mean‐squared observation‐minus‐forecast (OmF) TEC residuals. Substantial reduction in the global OmF for the 10 min assimilation‐forecast cycling suggests that a rapid cycling ionospheric data assimilation system can greatly improve the quality of the model forecast during geomagnetic storm conditions. Furthermore, updating the thermospheric state variables in the coupled thermosphere‐ionosphere forecast model in the assimilation step is an important factor in improving the trajectory of model forecasting. The shorter assimilation‐forecast cycling (10 min in this paper) helps to restrain unrealistic model error growth during the forecast step due to the imbalance among model state variables resulting from an inadequate state update, which in turn leads to a greater forecast accuracy.

The adsorption of 1-octanol at an air−water interface is studied theoretically and experimentally. A video-enhanced pendant bubble tensiometry is utilized for the measurement of relaxation of surface tension. Two types of processes were investigated:  the adsorption onto an initially clean air−water interface and the desorption out of a suddenly compressed interface which is originally at equilibrium. A theoretical simulation using the equilibrium surface tension is performed and it is concluded that there is no shift in controlling mechanism for the adsorption of 1-octanol molecules from an aqueous phase onto an initially clean air−water surface. The adsorption of 1-octanol onto a clean air-water interface is verified experimentally to be a diffusion-controlled process. A diffusion coefficient was computed by comparing these adsorption profiles with numerical solutions of bulk surfactant diffusion equation and the generalized Frumkin adsorption model. The re-equilibration of a compressed interface agrees well with a diffusion-controlled process. Lower bounds on the kinetic constants for the sorption process are inferred for octanol by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the desorption relaxation data.

The Formosa Satellite‐7/Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 (FORMOSAT‐7/COSMIC‐2) Global Navigation Satellite System radio occultation (RO) payload can provide global observations of slant total electron content (sTEC) with an unprecedentedly high spatial temporal resolution. Recently, a new ionospheric data assimilation system, the Community Gridpoint Statistical Interpolation (GSI) Ionosphere, is constructed with the National Oceanic and Atmospheric Administration GSI Ensemble Square Root Filter and the Global Ionosphere Plasmasphere and the Thermosphere Ionosphere Electrodynamic General Circulation Model. The paper demonstrates the capability of the GSI Ionosphere to improve the ionospheric specification and make a quantitative assessment of the impact of FORMOSAT‐7/COSMIC‐2 RO data on the ionospheric observing system simulation experiments conducted to calibrate key Ensemble Square Root Filter parameters that control detrimental effects of the sampling errors, particularly on the ensemble‐based estimation of the correlation between observations and model states, in order to yield high‐quality assimilation analysis. Results from the observing system simulation experiments show that (1) an ensemble size larger than 70 is recommended for assimilation of RO sTEC data with the GSI Ionosphere and (2) localizing the impact of observations around the tangent points in the horizontal direction with a length scale of 5,000 km is effective in improving assimilation analysis quality. Assimilation of sTEC data from FORMOSAT‐7/COSMIC‐2 can considerably improve the global ionospheric specification through the application of the GSI Ionosphere. The GSI Ionosphere can provide instantaneous global pictures of the ionosphere variability and help characterize day‐to‐day variability of the ionosphere and deepen our understanding of the observed day‐to‐day variability.