South America's tropopause variability in relation to global teleconnection (2001–2017): A GNSS-radio occultation assessment

Nascimento, Absalão Aranha; Awange, Joseph; Gonçalves, Rodrigo Mikosz; Khandu,

doi:10.1016/j.jastp.2020.105379

Cited by 3 publications

(2 citation statements)

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“…Indeed, that the tropopause, a boundary (i.e., 9–17 km) between the stratosphere and the troposphere could offer the possibility to quantitatively analyze upper level atmospheric characteristics in relation to regional climate variability and change over Africa is supported by regional studies that have been conducted, for example, in Australia (Khandu et al., 2011), Ganges‐Brahmaputra‐Meghna basin (Khandu et al., 2016), South America (Nascimento et al., 2020), and the tropical and subtropical tropopause regions (Tegtmeier et al., 2020). These studies were motivated by Santer, Sausen, et al.…”

Section: Introductionmentioning

confidence: 98%

“…Indeed, that the tropopause, a boundary (i.e., 9-17 km) between the stratosphere and the troposphere could offer the possibility to quantitatively analyze upper level atmospheric characteristics in relation to regional climate variability and change over Africa is supported by regional studies that have been conducted, for example, in Australia (Khandu et al, 2011), Ganges-Brahmaputra-Meghna basin (Khandu et al, 2016), South America (Nascimento et al, 2020), and the tropical and subtropical tropopause regions (Tegtmeier et al, 2020). These studies were motivated by and Santer, Wehner, et al (2003) who reported that the warming of the upper troposphere (UT, e.g., due to increased greenhouse gas emissions) and cooling of the lower stratosphere (LS, e.g., due to stratospheric ozone depletion) lead to a rise in tropopause height, indicating that climate change impacts can be quantified through UTLS monitoring.…”

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confidence: 97%

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GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability

et al. 2022

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Radiosonde data are important for understanding and monitoring the upper troposphere and lower stratosphere (UTLS) region. Over much of Africa, however, such data are lacking; consequently, the African UTLS is understudied, and potential proxies such as climate models and reanalysis products fail to fully capture the behavior of the UTLS. This study pioneers the use of Global Navigation Satellite System‐Radio Occultation (GNSS‐RO) data from 2001 to 2020 to address the radiosonde data gap over Africa and contributes to a better understanding of the tropopause (TP) characteristics under the influence of global and regional climate drivers over the continent. As a first step to using GNSS‐RO for infilling the radiosonde data gap over Africa, we analyzed the performance of GNSS‐RO (2001–2020) and reanalysis products (European Centre for Medium‐Range Weather Forecasts Reanalysis 5 (ERA5) and Modern‐Era Retrospective analysis for Research and Applications version 2 (MERRA‐2)) against radiosonde observations applying the Kling‐Gupta Efficiency metric. The analyses show that GNSS‐RO data from Challenging Mini‐satellite Payload, Gravity Recovery and Climate Experiment, Meteorological Operational, Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), and COSMIC‐2 are in good agreement with radiosonde measurements with differences being smaller than 1 K in the UTLS, thereby enabling infilling of missing radiosonde data in Africa during 2001–2020. By contrast, the smoothed vertical temperature profiles of reanalysis products lead to a warm bias of +0.8 K in ERA5 and +1.2 K in MERRA‐2 and these biases alter some vertical and temporal structure details, with possible implications on climate change detection and attribution. Furthermore, the analysis of GNSS‐RO data over Africa revealed: (a) the teleconnections of El Niño‐Southern Oscillation (ENSO), Quasi‐Biennial Oscillation (QBO), Indian Ocean Dipole (IOD), Madden‐Julian Oscillation (MJO), North Atlantic Oscillation (NAO) and Southern Annular Mode (SAM) at the tropopause boundary; (b) multiple coupled global climate drivers such as ENSO‐IOD, ENSO‐MJO, ENSO‐NAO, QBO‐IOD, and ENSO‐NAO‐MJO; (c) coupled global and regional climate drivers that influence the TP variability, for example, ENSO‐Inter Tropical Convergence Zone; and (d), the deep convection associated with the Asian Summer Monsoon and Tropical/African Easterly Jet also locally influence TP height. In conclusion, this study demonstrates the capability of GNSS‐RO to fill the vast radiosonde data gap over Africa. This opens the opportunity for further detailed studies toward a better understanding of the tropopause characteristics including localization, quantification of trends, and influences of global, regional, and coupled climate drivers.

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Section: Introductionmentioning

confidence: 98%

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confidence: 97%

GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability

et al. 2022

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The analytical indicators to explain the distribution of oases in arid zones using the Oases Integrated Analysis Model

Jing

Xue

Liu

et al. 2021

Ecological Indicators

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Stability of CubeSat Clocks and Their Impacts on GNSS Radio Occultation

et al. 2022

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Global Navigation Satellite Systems’ radio occultation (GNSS-RO) provides the upper troposphere-lower stratosphere (UTLS) vertical atmospheric profiles that are complementing radiosonde and reanalysis data. Such data are employed in the numerical weather prediction (NWP) models used to forecast global weather as well as in climate change studies. Typically, GNSS-RO operates by remotely sensing the bending angles of an occulting GNSS signal measured by larger low Earth orbit (LEO) satellites. However, these satellites are faced with complexities in their design and costs. CubeSats, on the other hand, are emerging small and cheap satellites; the low prices of building them and the advancements in their components make them favorable for the GNSS-RO. In order to be compatible with GNSS-RO requirements, the clocks of the onboard receivers that are estimated through the precise orbit determination (POD) should have short-term stabilities. This is essential to correctly time tag the excess phase observations used in the derivation of the GNSS-RO UTLS atmospheric profiles. In this study, the stabilities of estimated clocks of a set of CubeSats launched for GNSS-RO in the Spire Global constellation are rigorously analysed and evaluated in comparison to the ultra-stable oscillators (USOs) onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) satellites. Methods for improving their clock stabilities are proposed and tested. The results (i) show improvement of the estimated clocks at the level of several microseconds, which increases their short-term stabilities, (ii) indicate that the quality of the frequency oscillator plays a dominant role in CubeSats’ clock instabilities, and (iii) show that CubeSats’ derived UTLS (i.e., tropopause) atmospheric profiles are comparable to those of COSMIC-2 products and in situ radiosonde observations, which provided external validation products. Different comparisons confirm that CubeSats, even those with unstable onboard clocks, provide high-quality RO profiles, comparable to those of COSMIC-2. The proposed remedies in POD and the advancements of the COTS components, such as chip-scale atomic clocks and better onboard processing units, also present a brighter future for real-time applications that require precise orbits and stable clocks.

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South America's tropopause variability in relation to global teleconnection (2001–2017): A GNSS-radio occultation assessment

Cited by 3 publications

References 87 publications

GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability

GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability

The analytical indicators to explain the distribution of oases in arid zones using the Oases Integrated Analysis Model

Stability of CubeSat Clocks and Their Impacts on GNSS Radio Occultation

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