Ching-Yuang Huang

Ionospheric positive storm phases at the magnetic equator close to sunset

[1] During geomagnetic activities, perturbed electric fields at middle and low latitudes of the ionosphere may result from the effect of prompt penetration from high latitudes and the disturbance dynamo mechanism, respectively. The polarity of penetration electric fields depends on the orientation of the interplanetary magnetic field (IMF) Bz, and that of electric fields associated with the disturbance dynamo is almost opposite to that in the quiet time condition. Although a few hours are required to build up the perturbed electric fields through the disturbance dynamo mechanism, the dynamo electric fields can persist for several hours after geomagnetic activities cease. It turns out that the low‐latitude electric field disturbances associated with the disturbance dynamo mechanism should be more persistent than that associated with the direct penetration from the polar cap, especially for the period in the recovery phase. Model results show a significant, westward disturbance dynamo electric field at period close to sunset, but it seems not important in the empirical model. This perturbed electric field at sunset will weaken the intensity of the prereversal enhancement and of the following fountain effect in the storm time. Relative to the quiet time condition, it produces an enhancement in the total electron content. This phenomenon is seasonal. It only occurs at period close to equinox, when the hemispheric wind (summer to winter) is minimal. These theoretical results have been substantiated by model results of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model and by the global integration and modeling in this study. Both results show that the positive phase of the ionospheric storm at the magnetic equator close to sunset is produced by the westward disturbance dynamo electric field.

Observational Error Estimation of FORMOSAT-3/COSMIC GPS Radio Occultation Data

Abstract The Global Positioning System (GPS) radio occultation (RO) technique is becoming a robust global observing system. GPS RO refractivity is typically modeled at the ray perigee point by a “local refractivity operator” in a data assimilation system. Such modeling does not take into account the horizontal gradients that affect the GPS RO refractivity. A new observable (linear excess phase), defined as an integral of the refractivity along some fixed ray path within the model domain, has been developed in earlier studies to account for the effect of horizontal gradients. In this study, the error statistics of both observables (refractivity and linear excess phase) are estimated using the GPS RO data from the Formosa Satellite 3–Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) mission. The National Meteorological Center (NMC) method, which is based on lagged forecast differences, is applied for evaluation of the model forecast errors that are used for estimatio...

Low-latitude ionospheric effects of energetic electrons during a recurrent magnetic storm

We study a magnetosphere-ionosphere coupling at low latitudes during a moderate (corotating interaction regions/high-speed solar wind streams-driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (coronal mass ejection-driven) storms, quasi-trapped >30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere-ionosphere coupling through the quasi-trapped electrons also may take place. Data from NOAA/Polar-orbiting Operational Environmental Satellite and Japanese Greenhouse gases Observing Satellite were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps, radiotomography reconstructions from beacon data and COSMIC/FORMOSAT-3 radio occultation measurements, we have observed an unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F layer at low latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.

Meteorology-hydrology study targets Typhoon Nari and Taipei flood

Typhoon Nari struck Taiwan on 16 September 2001, taking 92 lives. Analysis reveals that the storms heavy rains were due to warmer ocean temperatures, Naris unique track and slow-moving speed, and the terrain of Taiwan. Analysis further suggests that the heavy rains in Nari contained many small raindrops. The typhoon rains overwhelmed existing flood protection capacities downstream of the Chi-Lung River in a part of Taipei that has no regulatory reservoirs, resulting in major flooding. Preliminary findings underscore several key issues for future study, the goal of which will be to improve quantitative precipitation estimation/prediction, hydrologic modeling, and flood prediction.

Applications of COSMIC Radio Occultation Data from the Troposphere to Ionosphere and Potential Impacts of COSMIC-2 Data

What: More than 130 people representing 15 nations met to highlight accomplishments in global positioning system (GPS) radio occultation (RO) operations and algorithm development, meteorology, climate, and ionospheric applications using COSMIC data. When: 30 October–1 November 2012 Where: Boulder, Colorado APPLICATIONS OF COSMIC RADIO OCCULTATION DATA FROM THE TROPOSPHERE TO IONOSPHERE AND POTENTIAL IMPACTS OF COSMIC-2 DATA

Evaluating the Impact of the COSMIC RO Bending Angle Data on Predicting the Heavy Precipitation Episode on 16 June 2008 during SoWMEX-IOP8

AbstractGlobal positioning system (GPS) radio occultation (RO) data have been broadly used in global and regional numerical weather predictions. Assimilation with the bending angle often performs better than refractivity, which is inverted from the bending angle under spherical assumption and is sometimes associated with negative biases at the lower troposphere; however, the bending angle operator also requires a higher model top as used in global models. This study furnishes the feasibility of bending-angle assimilation in the prediction of heavy precipitation systems with a regional model. The local RO operators for simulating bending angle and refractivity are implemented in the Weather Research and Forecasting (WRF)–local ensemble transform Kalman filter (LETKF) framework. The impacts of assimilating RO data from the Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) using both operators are evaluated on the prediction of a heavy precipitation episode during Southwest Monso...

A numerical investigation of the convective systems in the vicinity of southern Taiwan associated with Typhoon Fanapi (2010): Formation mechanism of double rainfall peaks

The westbound Typhoon Fanapi (2010) brought 872 mm daily rainfall over the coastal plain in southern Taiwan, which is comparable to the extreme rainfall of 1080 mm over the southern Central Mountain Range (CMR). In this study, the Weather Research and Forecast model was used to investigate the formation mechanism of the two rainfall peaks and the associated dynamics of the convective systems in the vicinity of southern Taiwan. As the vortex that deflects somewhat southward near landfall moves over the CMR, the vortex slows down significantly during westward departure and induces strong near-coastal convergence at lower levels with the westerly to southwesterly outer flow. The associated intense latent heating of the near-coastal rainfall greatly contributes to positive potential vorticity (PV) with enhanced vorticity stretching near the convex eyewall when the vortex becomes more asymmetric and longitudinally elongated. The positive PV tendency near the coast is induced not only by vertical differential diabatic heating (DDH) but also by the longitudinal DDH mainly associated with positive vorticity tilting. The longitudinal DDH indeed dominates all other processes in the PV generation inside the eyewall further offshore, which is vital to the maintenance of the eyewall with the strong banded convergence and is special to typical intense cyclones over the open ocean. The formation of the double intense rainfall peaks cannot occur without a precise departing track near the southwest coast in association with the slowdown of the vortex core when the CMR height is significantly reduced or latent heating is deactivated after landfall.

An impact study of GPS radio occultation observations on frontal rainfall prediction with a local bending angle operator

AbstractThe impact of global positioning system (GPS) radio occultation (RO) soundings on the prediction of severe mei-yu frontal rainfall near Taiwan in June 2012 was investigated in this study using a developed local bending angle (LBA) operator. Two operators for local refractivity (REF) and nonlocal refractivity [excess phase (EPH)] were also used for comparisons. The devised LBA simplifies the calculation of the Abel transform in inverting model local refractivity without a loss of accuracy. These operators have been implemented into the three-dimensional variational data assimilation system of the Weather Research and Forecasting (WRF) Model to assimilate GPS RO soundings available from the Formosa Satellite Mission 3/Constellation Observing Systems for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC). The RO data are found to be beneficial to the WRF forecast of local severe rainfall in Taiwan. Characteristics of assimilation performance and innovation for the three operators are discussed. ...