Equatorial waves, diurnal tides and small-scale thermal variability in the tropical lower stratosphere from COSMIC-2 radio occultation

AbstractGlobal positioning system (GPS) radio occultation (RO) is capable of retrieving vertical profiles of atmospheric parameters with high resolution (<100 m), which can be achieved in spherically symmetric atmosphere. Horizontal inhomogeneity of real atmosphere results in representativeness errors of retrieved profiles. In most cases these errors increase with a decrease of vertical scales of atmospheric structures and may not allow one to fully utilize the physical resolution of RO. Also, GPS RO–retrieved profiles are affected by observational noise of different types, which, in turn, affect the representation of small-scale atmospheric structures. This study investigates the effective resolution and optimal smoothing of GPS RO–retrieved temperature profiles using high-pass filtering and cross correlation with collocated high-resolution radiosondes. The effective resolution is a trade-off between representation of real atmospheric structures and suppression of observational noise, which varies for different latitudes (15°S–75°N) and altitudes (10–27 km). Our results indicate that at low latitudes the effective vertical resolution is about 0.2 km near the tropical tropopause layer and about 0.5 km in the lower stratosphere. The best resolution of 0.1 km is at the cold-point tropical tropopause. The effective resolutions at the midlatitudes are slightly worse than at low latitudes, varying from ~0.2 to 0.6 km. At high latitudes, the effective resolutions change notably with altitude from ~0.2 km at 10–15 km to ~1.4 km at 22–27 km. Our results suggest that the atmospheric inhomogeneity plays an important role in the representation of the vertical atmospheric structures by RO measurements.

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Measurements of the upper troposphere and lower stratosphere during tropical cyclones using the GPS radio occultation technique

Advances in Space Research ◽

10.1016/j.asr.2010.05.031 ◽

2011 ◽

Vol 47 (2) ◽

pp. 348-355 ◽

Cited By ~ 7

Author(s):

Riccardo Biondi ◽

Torsten Neubert ◽

Stig Syndergaard ◽

Johannes Nielsen

Keyword(s):

Tropical Cyclones ◽

Radio Occultation ◽

Lower Stratosphere ◽

Upper Troposphere ◽

Gps Radio Occultation

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Atmospheric Climate Change Detection by Radio Occultation Data Using a Fingerprinting Method

Journal of Climate ◽

10.1175/2011jcli3966.1 ◽

2011 ◽

Vol 24 (20) ◽

pp. 5275-5291 ◽

Cited By ~ 35

Author(s):

Bettina C. Lackner ◽

Andrea K. Steiner ◽

Gabriele C. Hegerl ◽

Gottfried Kirchengast

Keyword(s):

Climate Change ◽

Change Detection ◽

Confidence Level ◽

Geopotential Height ◽

Radio Occultation ◽

Lower Stratosphere ◽

Quality Data ◽

Climate Change Signal ◽

High Quality ◽

Climate Change Detection

Abstract The detection of climate change signals in rather short satellite datasets is a challenging task in climate research and requires high-quality data with good error characterization. Global Navigation Satellite System (GNSS) radio occultation (RO) provides a novel record of high-quality measurements of atmospheric parameters of the upper-troposphere–lower-stratosphere (UTLS) region. Because of characteristics such as long-term stability, self calibration, and a very good height resolution, RO data are well suited to investigate atmospheric climate change. This study describes the signals of ENSO and the quasi-biennial oscillation (QBO) in the data and investigates whether the data already show evidence of a forced climate change signal, using an optimal-fingerprint technique. RO refractivity, geopotential height, and temperature within two trend periods (1995–2010 intermittently and 2001–10 continuously) are investigated. The data show that an emerging climate change signal consistent with the projections of three global climate models from the Coupled Model Intercomparison Project cycle 3 (CMIP3) archive is detected for geopotential height of pressure levels at a 90% confidence level both for the intermittent and continuous period, for the latter so far in a broad 50°S–50°N band only. Such UTLS geopotential height changes reflect an overall tropospheric warming. 90% confidence is not achieved for the temperature record when only large-scale aspects of the pattern are resolved. When resolving smaller-scale aspects, RO temperature trends appear stronger than GCM-projected trends, the difference stemming mainly from the tropical lower stratosphere, allowing for climate change detection at a 95% confidence level. Overall, an emerging trend signal is thus detected in the RO climate record, which is expected to increase further in significance as the record grows over the coming years. Small natural changes during the period suggest that the detected change is mainly caused by anthropogenic influence on climate.

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Gravity-wave effects on tracer gases and stratospheric aerosol concentrations during the 2013 ChArMEx campaign

10.5194/acp-2015-889 ◽

2016 ◽

Cited By ~ 2

Author(s):

Fabrice Chane Ming ◽

Damien Vignelles ◽

Fabrice Jegou ◽

Gwenael Berthet ◽

Jean-Batiste Renard ◽

...

Keyword(s):

Gravity Wave ◽

Lower Stratosphere ◽

Weather Forecasting ◽

Stratospheric Aerosol ◽

Thin Layers ◽

Vertical Wind ◽

Specific Humidity ◽

Small Scale ◽

Strong Activity ◽

Dynamical Parameters

Abstract. Coupled balloon-borne observations of Light Optical Aerosol Counter (LOAC), M10 meteorological global positioning system (GPS) sondes, ozonesondes and GPS radio occultation data, are examined to identify gravity-wave (GW) induced fluctuations on tracer gases and on the vertical distribution of stratospheric aerosol concentrations during the 2013 ChArMEx (Chemistry-Aerosol Mediterranean Experiment) campaign. Observations reveal signatures of GWs with short vertical wavelengths less than 4 km in dynamical parameters and tracer constituents which are also correlated with the presence of thin layers of strong local enhancements of aerosol concentrations in the upper troposphere and the lower stratosphere. In particular, this is evident from a case study above Ile du Levant (43.02 °N, 6.46 °E) on 26–29 July 2013. Observations show a strong activity of dominant mesoscale inertia GWs with horizontal and vertical wavelengths of 370–510 km and 2–3 km respectively, and periods of 10–13 h propagating southward at altitudes of 13–20 km and eastward above 20 km during 27–28 July which is also captured by the European Center for Medium range Weather Forecasting (ECMWF) analyses. Ray-tracing experiments indicate the jet-front system to be the source of observed GWs. Simulated vertical profiles of dynamical parameters with large stratospheric vertical wind maximum oscillations ± 40 mms−1 are produced for the dominant mesoscale GW using the simplified linear GW theory. Parcel advection method reveals signatures of GWs in the ozone mixing ratio and the specific humidity. Simulated vertical wind perturbations of the dominant GW and small-scale perturbations of aerosol concentration (aerosol size of 0.2–0.7 μm) are in phase in the lower stratosphere. Present results support the importance of vertical wind perturbations in the GW-aerosol relation. The observed mesoscale GW induces a strong modulation of the amplitude of tracer gases and the stratospheric aerosol background.

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COSMIC Radio Occultation Processing: Cross-Center Comparison and Validation

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2011jtecha1489.1 ◽

2011 ◽

Vol 28 (6) ◽

pp. 737-751 ◽

Cited By ~ 24

Author(s):

Michael E. Gorbunov ◽

A. V. Shmakov ◽

Stephen S. Leroy ◽

Kent B. Lauritsen

Keyword(s):

Data Processing ◽

Radio Occultation ◽

Weather Prediction ◽

Processing System ◽

Fourier Integral ◽

Small Scale ◽

Cosmic Radio ◽

Structural Uncertainty ◽

Height Range ◽

The Tropics

Abstract A radio occultation data processing system (OCC) was developed for numerical weather prediction and climate benchmarking. The data processing algorithms use the well-established Fourier integral operator–based methods, which ensure a high accuracy of retrievals. The system as a whole, or in its parts, is currently used at the Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) Satellite Application Facility at the Danish Meteorological Institute, German Weather Service, and Wegener Center for Climate and Global Change. A statistical comparison of the inversions of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data by the system herein, University Corporation for Atmospheric Research (UCAR) data products, and ECMWF analyses is presented. Forty days of 2007 and 2008 were processed (from 5 days in the middle of each season) for the comparison of OCC and ECMWF, and 20 days of April 2009 were processed for the comparison of OCC, UCAR, and ECMWF. The OCC and UCAR inversions are consistent. For the tropics, the systematic difference between OCC and UCAR in the retrieved refractivity in the 2–30-km height interval does not exceed 0.1%; in particular, in the 9–25-km interval it does not exceed 0.03%. Below 1 km in the tropics the OCC – UCAR bias reaches 0.2%, which is explained by different cutoff and filtering schemes implemented in the two systems. The structure of the systematic OCC – ECMWF difference below 4 km changes in 2007, 2008, and 2009, which is explained by changes in the ECMWF analyses and assimilation schemes. It is estimated that in the 4–30-km height range the OCC occultation processing system obtains refractivities with a bias not exceeding 0.2%. The random error ranges from 0.3%–0.5% in the upper troposphere–lower stratosphere to about 2% below 4 km. The estimate of the bias below 4 km can currently be done with an accuracy of 0.5%–1% resulting from the structural uncertainty of the radio occultation (RO) data reflecting the insufficient knowledge of the atmospheric small-scale structures and instrumental errors. The OCC – UCAR bias is below the level of the structural uncertainty.

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Equatorial Waves in Opposite QBO Phases

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3514.1 ◽

2011 ◽

Vol 68 (4) ◽

pp. 839-862 ◽

Cited By ~ 24

Author(s):

Gui-Ying Yang ◽

Brian J. Hoskins ◽

Julia M. Slingo

Keyword(s):

Group Velocity ◽

Lower Stratosphere ◽

Phase Speed ◽

Kelvin Waves ◽

Western Hemisphere ◽

Equatorial Waves ◽

Vertical Wavelength ◽

Quasi Biennial Oscillation ◽

Zonal Wavenumber ◽

The Waves

Abstract A methodology for identifying equatorial waves is used to analyze the multilevel 40-yr ECMWF Re-Analysis (ERA-40) data for two different years (1992 and 1993) to investigate the behavior of the equatorial waves under opposite phases of the quasi-biennial oscillation (QBO). A comprehensive view of 3D structures and of zonal and vertical propagation of equatorial Kelvin, westward-moving mixed Rossby–gravity (WMRG), and n = 1 Rossby (R1) waves in different QBO phases is presented. Consistent with expectation based on theory, upward-propagating Kelvin waves occur more frequently during the easterly QBO phase than during the westerly QBO phase. However, the westward-moving WMRG and R1 waves show the opposite behavior. The presence of vertically propagating equatorial waves in the stratosphere also depends on the upper tropospheric winds and tropospheric forcing. Typical propagation parameters such as the zonal wavenumber, zonal phase speed, period, vertical wavelength, and vertical group velocity are found. In general, waves in the lower stratosphere have a smaller zonal wavenumber, shorter period, faster phase speed, and shorter vertical wavelength than those in the upper troposphere. All of the waves in the lower stratosphere show an upward group velocity and downward phase speed. When the phase of the QBO is not favorable for waves to propagate, their phase speed in the lower stratosphere is larger and their period is shorter than in the favorable phase, suggesting Doppler shifting by the ambient flow and a filtering of the slow waves. Tropospheric WMRG and R1 waves in the Western Hemisphere also show upward phase speed and downward group velocity, with an indication of their forcing from middle latitudes. Although the waves observed in the lower stratosphere are dominated by “free” waves, there is evidence of some connection with previous tropical convection in the favorable year for the Kelvin waves in the warm water hemisphere and WMRG and R1 waves in the Western Hemisphere, which is suggestive of the importance of convective forcing for the existence of propagating coupled Kelvin waves and midlatitude forcing for the existence of coupled WMRG and R1 waves.

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