Probing a Hurricane's Eye with the GPS Radio Occulation Technique
No abstract available
Radio Occulation (RO)↗
Engineering topics
Ao, Chi O.
Publications and source records attributed to Ao, Chi O..
Climate and Weather Sensors on Iridium-NEXT: A Combined GPS-RO and WindCam System for PBL Remote Sensing
No abstract available
weather forecast↗
Assessment of Open-Loop Tracking Occultation Data from COSMIC
An assessment of open-loop tracking occultation data from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is presented.
COSMIC↗
Quasi-biennial Oscillations (QBO) as seen in GPS/CHAMP Tropospheric and Ionospheric Data
A viewgraph presentation on Quasi-biennial Oscillations (QBO) from Global Positioning System/Challenging Mini-Satellite Payload (GPS/CHAMP) tropospheric and ionsopheric data is shown. The topics include: 1) A brief review of QBO; 2) Characteristics of small-scale oscillations in GPS/CHAMP 50-Hz raw measurements; 3) Variations of lower atmospheric variances; and 4) Variations of E-region variances.
gravity waves↗
Sensitivity of Stratospheric Retrievals from Radio Occultations on Upper Boundary Conditions
The main uncertainty in the stratospheric retrievals from GPS radio occultation (RO) measurements comes from the lack of reliable measurements in the upper stratosphere and above where the bending due to the neutral atmosphere is weak and residual ionospheric effects are strong. In this work, we quantify the bias and uncertainty of the refractivity and temperature retrievals due to different upper boundary strategies using a simulation study. We use lidar refractivity and temperature profiles as the input states in generating the synthetic occultations. Random noise levels commensurate with the CHAMP RO measurements are then added to the simulated data. Through this study, the sensitivity of stratospheric retrievals to upper boundary methods and parameters are examined. Such error characterizations are important prerequisites towards the effective use of GPS RO data in climate monitoring.
GPS↗
Sporadic E Morphology from GPS-CHAMP Radio Occultation
The scintillations of phase and amplitude in terms of signal-to-noise ratio (SNR) of the GPS radio occultation signal are caused by thin ionization layers. These thin irregular electron density layers in the E region ionosphere are often called sporadic E (Es). For a monthly retrieval of Es morphology we use the variances of the phase and SNR fluctuations of worldwide ~6000 GPS/CHAMP occultations in the E region. The Es climatology is studied globally with the SNR and phase variances in terms of monthly zonal means, seasonal maps, and diurnal and long-term variations. The zonal mean variances reveal strong, extended Es activities at summertime midlatitudes but weak, confined activities in wintertime high latitudes, peaking at ~105 km. Global maps at 105-km altitude show clear dependence of Es activities on the geomagnetic dip angle, where the summertime midlatitude Es occurs mostly at dip angles of 30 deg. - 60 deg. and the wintertime high-latitude enhancement occurs mostly at dip angles greater than 80 deg. The midlatitude Es variances exhibit a strong semidiurnal variation with peak hours near 0800 1000 and 2000 local solar time, respectively. The peak hours are delayed slightly with decreasing height, suggesting influences from the semidiurnal tide. To provide more insights on the observed SNR and phase variances, we model radio wave propagation for the CHAMP observing geometry under several perturbed cases in the E region ionosphere. The model simulations indicate that the SNR variance has the maximum response to Es perturbations at vertical wavelengths of 1.2 km, whereas the phase response maximizes at ~2 km (for the 1-s variance analysis). The characteristic scale depends little on the truncation time used in the SNR variance analysis, but it increases with the truncation time for the phase variances. Initial studies show that reasonable global Es morphology can be produced on a monthly and seasonal basis with the CHAMP one-antenna occultations. Better results from other existing and upcoming GPS occultation missions are anticipated in future studies, and they will significantly improve our understanding of this important phenomenon.
signal to noise ration (SNR)↗
Thermal Structure of the TTL and Its Relation to Stratospheric-Tropospheric Exchange of Water
This document describes the annual cycle of the trajectory track line (TTL) fine scale thermal structure as captured by global positioning system (GPS) radio occultation and the pressure levels of the East Meets West Foundation (EMWF) weather analysis. This annual cycle is compared to the annual cycle in water concentrations measured by the HALogen Occultation Experiment (HALOE). A comparison between saturation mixing ratios at the temperatures captured by GPS radio occultation and HALOE concentrations of water vapor shows an annual cycle that is dominated by supersaturation in the boreal winter months, when the upward mass fluxes are larger, and subsaturation in the summer. The longitudinal dependence of these cycles is discussed as well as the possible implications for the seasonality of stratospheric-troposheric exchanges of water.
climates↗
Towards new scientific observations from GPS occultations: advances in retrieval methods
We will present recent innovations in extracting scientifically useful information from the phase and amplitude of received GPS transmissions, and discuss the technical challenges that need to be overcome to achieve new scientific results.
Schroder, Thomas↗
Tropical Tropopause Structure and Processes as Observed with GPS Radio Occultation
The vertical temperature structure of the tropical atmosphere has been explained as controlled by the combined effect of three green house gases: water vapor, carbon dioxide, and ozone. Absorption by water vapor of the light reflected off the Earth's surface would determine the temperature lapse rate in the lower troposphere up to the bottom of the Tropical Transition Layer (TTL); radiative absorption by carbon dioxide would dominate the temperature lapse rate between the bottom of the TTL and the coldest point in the upper-troposphere, the cold point tropopause (CPT), and; absorption of incoming solar radiation by ozone would control the temperature above the CPT. The TTL region can thus be very sensitive to changes in the relative abundances of these greenhouse gases. In this contribution we describe the seasonal evolution of temperature profiles in the TTL and their longitudinal structure using GPS radio occultation.
global positioning system (GPS)↗
Comparison of GPS/SAC-C and MIPAS/ENVISAT temperature profiles and its implementation for EOS AURA-MLS observations
A new generation GPS flight receiver was launched on the Argentinian satellite SAC-C in 2001. It has demonstrated the potential applicability for the continuous monitoring of the earth's atmosphere with radio occultation technology, and providing high vertical resolution profiles of temperature and water vapour data complementary to other sounding techniques.
atmospheric science temperature↗