Ying-Hwa Kuo

THE COSMIC/FORMOSAT-3 MISSION : Early Results

The radio occultation (RO) technique, which makes use of radio signals transmitted by the global positioning system (GPS) satellites, has emerged as a powerful and relatively inexpensive approach for sounding the global atmosphere with high precision, accuracy, and vertical resolution in all weather and over both land and ocean. On 15 April 2006, the joint Taiwan-U.S. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3, hereafter COSMIC) mission, a constellation of six microsatellites, was launched into a 512-km orbit. After launch the satellites were gradually deployed to their final orbits at 800 km, a process that took about 17 months. During the early weeks of the deployment, the satellites were spaced closely, offering a unique opportunity to verify the high precision of RO measurements. As of September 2007, COSMIC is providing about 2000 RO soundings per day to support the research and operational communities. COSMIC RO dat...

Analysis and validation of GPS/MET data in the neutral atmosphere

The Global Positioning System/Meteorology ( GPS/MET) Program was established in 1993 by the University Corporation for Atmospheric Research ( UCAR) to demonstrate active limb sounding of the Earths atmosphere using the radio occultation technique. The demonstration system observes occulted GPS satellite signals received by a low Earth orbiting ( LEO) satellite, MicroLab-1, launched April 3,1995. The system can profile ionospheric electron density and neutral atmospheric properties. Neutral atmospheric refractivity, density, pressure, and temperature are derived at altitudes where the amount of water vapor is low. At lower altitudes, vertical profiles of density, pressure, and water vapor pressure can be derived from the GPS/MET refractivity profiles if temperature data from an independent source are available. This paper describes the GPS/MET data analysis procedures and validates GPS/MET data with statistics and illustrative case studies. We compare more than 1200 GPS/MET neutral atmosphere soundings to correlative data from operational global weather analyses, radiosondes, and the GOES, TOVS, UARS/MLS and HALOE orbiting atmospheric sensors. Even though many GPS/MET soundings currently fail to penetrate the lowest 5 km of the troposphere in the presence of significant water vapor, our results demonstrate 1°C mean temperature agreement with the best correlative data sets between 1 and 40 km. This and the fact that GPS/MET observations are all-weather and self-calibrating suggests that radio occultation technology has the potential to make a strong contribution to a global observing system supporting weather prediction and weather and climate research.

GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results

Abstract This paper provides an overview of the methodology of and describes preliminary results from an experiment called GPS/MET (Global Positioning System/Meteorology), in which temperature soundings are obtained from a low Earth-orbiting satellite using the radio occultation technique. Launched into a circular orbit of about 750-km altitude and 70° inclination on 3 April 1995, a small research satellite, MicroLab 1, carried a laptop-sized radio receiver. Each time this receiver rises and sets relative to the 24 operational GPS satellites, the GPS radio waves transect successive layers of the atmosphere and are bent (refracted) by the atmosphere before they reach the receiver, causing a delay in the dual-frequency carrier phase observations sensed by the receiver. During this occultation, GPS limb sounding measurements are obtained from which vertical profiles of atmospheric refractivity can be computed. The refractivity is a function of pressure, temperature, and water vapor and thus provides informat...

Description of the Penn State/NCAR Mesoscale Model: Version 4 (MM4)

The report describes a limited-area, hydrostatic, primitive equation numerical model developed by the Pennsylvania State University and the National Center for Atmospheric Research (NCAR). The model is known as the Penn State/NCAR Mesoscale Model, Version 4, or MM4. The report documents the continuous-model equations and their finite-difference analogs, the horizontal and vertical grid structures, the lateral boundary conditions, and the parameterization of physical processes in the model. These processes include surface fluxes of heat, moisture and momentum, the turbulent transport of these quantities in the planetary boundary layer and the free atmosphere, horizontal diffusion, and the release of latent heat in convective and nonconvective clouds. The report also provides references to other reports and publications that document the modeling system and applications of the system to the simulation of atmospheric phenomena.

Typhoons Affecting Taiwan: Current Understanding and Future Challenges

Of all the natural disasters occurring in Taiwan, tropical cyclones are the most serious. Over a 20-yr period, Taiwan was hit by an average of 3.7 typhoons per year. These storms can produce heavy rainfall and strong winds, leading to severe damage to agriculture and industry, and serious loss of human life. An outstanding example is Typhoon Herb, which made landfall in Taiwan on 31 July 1996. Typhoon Herb took 70 lives and caused an estimated

Four-Dimensional Variational Data Assimilation for WRF: Formulation and Preliminary Results

5 billion of damage to agriculture and property. Accurate prediction of the track, intensity, precipitation, and strong winds for typhoons affecting Taiwan is not an easy task. The lack of meteorological data over the vast Pacific Ocean and the strong interaction between typhoon circulation and Taiwans mesoscale Central Mountain range are two major factors that make the forecasting of typhoons in the vicinity of Taiwan highly challenging. Improved understanding of the dynamics of typhoon circulation and their interaction with the Taiwan terrain is needed for more ...

Diagnosis of an intense atmospheric river impacting the pacific northwest: Storm summary and offshore vertical structure observed with COSMIC satellite retrievals

Abstract The Weather Research and Forecasting (WRF) model–based variational data assimilation system (WRF-Var) has been extended from three- to four-dimensional variational data assimilation (WRF 4D-Var) to meet the increasing demand for improving initial model states in multiscale numerical simulations and forecasts. The initial goals of this development include operational applications and support to the research community. The formulation of WRF 4D-Var is described in this paper. WRF 4D-Var uses the WRF model as a constraint to impose a dynamic balance on the assimilation. It is shown to implicitly evolve the background error covariance and to produce the flow-dependent nature of the analysis increments. Preliminary results from real-data 4D-Var experiments in a quasi-operational setting are presented and the potential of WRF 4D-Var in research and operational applications are demonstrated. A wider distribution of the system to the research community will further develop its capabilities and to encoura...

Rainfall Assimilation through an Optimal Control of Initial and Boundary Conditions in a Limited-Area Mesoscale Model

Abstract This study uses the new satellite-based Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission to retrieve tropospheric profiles of temperature and moisture over the data-sparse eastern Pacific Ocean. The COSMIC retrievals, which employ a global positioning system radio occultation technique combined with “first-guess” information from numerical weather prediction model analyses, are evaluated through the diagnosis of an intense atmospheric river (AR; i.e., a narrow plume of strong water vapor flux) that devastated the Pacific Northwest with flooding rains in early November 2006. A detailed analysis of this AR is presented first using conventional datasets and highlights the fact that ARs are critical contributors to West Coast extreme precipitation and flooding events. Then, the COSMIC evaluation is provided. Offshore composite COSMIC soundings north of, within, and south of this AR exhibited vertical structures that are meteorologically consistent with satellit...

The Integrated Effect of Condensation in Numerical Simulations of Extratropical Cyclogenesis

Abstract To assess the impact of rainfall observations on short-range forecasts of precipitation, and to improve our understanding of the physical processes responsible for the development of a mesoscale convective system (MCS) associated with the dryline that occurred on 10 April 1979 in the midwestern United States, a series of four-dimensional variational data assimilation experiments was conducted based on the special dataset collected in the Severe Environmental Storm and Mesoscale Experiment. A nonhydrostatic mesoscale model (MM5) with a relatively simple moist physics and its adjoint were used for both the model simulation and data assimilation. A previous numerical simulation of this MCS, based on conventional initialization procedures, failed to correctly simulate the location and intensity of the observed rainfall. This is attributed to the lack of mesoscale details in the models initial conditions for the low-level moisture convergence and the upper-level disturbances related to the upper-leve...

Assimilation of Doppler Radar Observations with a Regional 3DVAR System: Impact of Doppler Velocities on Forecasts of a Heavy Rainfall Case

Abstract By combining traditional sensitivity studies with techniques that focus on the conservation and invertibility properties of Ertels potential vorticity (PV), we illustrate the effect of latent heating on the structure and evolution of three simulated extratropical cyclones. The cases include one continental cyclone development (15 December 1987), which we examine extensively, and two cyclones over the western Atlantic Ocean (6 January 1983 and 5 January 1985) of somewhat greater intensity, which are diagnosed to assess the generality of our findings for the continental case. Each storm featured a weaker cyclonic low-level circulation when latent heating was removed from the simulation, but the magnitude of the effect varied greatly. In all cases, the difference in intensity was attributed to velocities associated with a positive, condensation-produced PV anomaly above the warm front. The amplification of the surface thermal perturbations was not strongly altered in even the case most affected by ...