Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa
<p>This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented....
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/9541/2019/acp-19-9541-2019.pdf |
| Summary: | <p>This study analyzes the characteristics of GPS
tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase
residuals) during the passage of mesoscale convective systems (MCSs) and
evaluates their sensitivity to the research-level GPS data processing
strategy implemented. Here, we focus on MCS events observed during the
monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic
environments between the Guinean coast and the Sahel. This contrast is well
sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a
3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS
software packages, were analyzed and intercompared. First, the case of a
MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a
strong impact of the MCS on GPS estimates and post-fit residuals when the
GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of
detecting changes in the structure and dynamics of the MCS. However, the sensitivity
is different depending on the tropospheric modeling approach adopted
in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of
ZWDs and gradients is well suited for detecting the
small-scale, short-lived, convective cells, while the post-fit residuals
remain quite small. With GAMIT, the lower temporal sampling of the estimated
parameters (hourly for ZWDs and daily for gradients) is not
sufficient to capture the rapid delay variations associated with the passage
of the MCS, but the post-fit phase residuals clearly reflect the presence of
a strong refractivity anomaly. The results are generalized with a composite
analysis of 414 MCS events observed over the 3-year period at the six GPS
stations with the GIPSY-OASIS estimates. A systematic peak is found in the
ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS
propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and
complementary information on MCSs passing over or in the vicinity of a GPS
station.</p> |
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| ISSN: | 1680-7316 1680-7324 |