scholarly journals Orographic and convective gravity waves above the Alps and Andes Mountains during GPS radio occultation events – a case study

2018 ◽  
Vol 11 (6) ◽  
pp. 3523-3539 ◽  
Author(s):  
Rodrigo Hierro ◽  
Andrea K. Steiner ◽  
Alejandro de la Torre ◽  
Peter Alexander ◽  
Pablo Llamedo ◽  
...  
Keyword(s):  
Case Studies ◽  
Gravity Waves ◽  
Radio Occultation ◽  
Convective Activity ◽  
Mountain Waves ◽  
Gps Radio Occultation ◽  
Convective Systems ◽  
The Andes ◽  
The Alps

Abstract. Gravity waves (GWs) and convective systems play a fundamental role in atmospheric circulation, weather, and climate. Two usual main sources of GWs are orographic effects triggering mountain waves and convective activity. In addition, GW generation by fronts and geostrophic adjustment must also be considered. The utility of Global Positioning System (GPS) radio occultation (RO) observations for the detection of convective systems is tested. A collocation database between RO events and convective systems over subtropical to midlatitude mountain regions close to the Alps and Andes is built. From the observation of large-amplitude GW structures in the absence of jets and fronts, subsets of RO profiles are sampled. A representative case study among those considered at each region is selected and analyzed. The case studies are investigated using mesoscale Weather Research and Forecasting (WRF) simulations, ERA-Interim reanalysis data, and measured RO temperature profiles. The absence of fronts or jets during both case studies reveals similar relevant GW features (main parameters, generation, and propagation). Orographic and convective activity generates the observed GWs. Mountain waves above the Alps reach higher altitudes than close to the Andes. In the Andes case, a critical layer prevents the propagation of GW packets up to stratospheric heights. The case studies are selected also because they illustrate how the observational window for GW observations through RO profiles admits a misleading interpretation of structures at different altitude ranges. From recent results, the distortion introduced in the measured atmospheric vertical wavelengths by one of the RO events is discussed as an illustration. In the analysis, both the elevation angle of the sounding path (line of tangent points) and the gravity wave aspect ratio estimated from the simulations and the line of sight are taken into account. In both case studies, a considerable distortion, over- and underestimation of the vertical wavelengths measured by RO, may be expected.

scholarly journals Orographic and convective gravity waves above the Alps and Andes mountains during GPS radio occultation events – a case study

2017 ◽  
Author(s):  
Rodrigo Hierro ◽  
Andrea K. Steiner ◽  
Alejandro de la Torre ◽  
Peter Alexander ◽  
Pablo Llamedo ◽  
...  
Keyword(s):  
Case Studies ◽  
Gravity Waves ◽  
Radio Occultation ◽  
Elevation Angle ◽  
Convective Activity ◽  
Mountain Waves ◽  
Gps Radio Occultation ◽  
Convective Systems ◽  
The Alps

Abstract. Gravity waves (GW) and convective systems play a fundamental role in atmospheric circulation, weather, and climate. The main sources of GW are orographic effects triggering mountain waves and convective activity. We test the utility of Global Positioning System (GPS) radio occultation (RO) observations for the investigation of convective systems and GW over orographic regions in Europe and South America. We build a collocation database between RO events and convective systems over sub-tropical to mid-latitude mountain regions close to the Alps and Andes. Subsets of RO profiles are sampled and a case study is selected for each region. From mesoscale numerical simulations, we analyze relevant gravity waves features (main parameters, generation and propagation), mainly from orographic and convective activity origin for the case studies considered. Similar GW regimes and dominant vertical and horizontal wavelengths, from convective and orographic sources, are found in both regions. Mountain waves above the Alps are found to reach higher altitudes than close to the Andes, as the background subtropical jet above this region constrains the propagation of GW packets up to stratospheric heights. From recent results, the distortion introduced in the measured atmospheric vertical gravity wavelength by one of the RO events is illustratively discussed. In our analysis we take into account both the elevation angle of the sounding path (line of tangent points) and the gravity wave aspect ratio estimated from the simulations and the line of sight. In both case studies, a considerable distortion and underestimation of the vertical wavelengths measured by RO may be expected.

scholarly journals Gravity waves above the Andes detected from GPS radio occultation temperature profiles: Jet mechanism?

2006 ◽  
Vol 33 (24) ◽  
Author(s):  
A. de la Torre ◽  
P. Alexander ◽  
P. Llamedo ◽  
C. Menéndez ◽  
T. Schmidt ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Radio Occultation ◽  
Temperature Profiles ◽  
Gps Radio Occultation ◽  
The Andes

scholarly journals A gravity waves study close to the Andes mountains in Patagonia and Antarctica with GPS radio occultation observations

2010 ◽  
Vol 28 (2) ◽  
pp. 587-595 ◽  
Author(s):  
P. Alexander ◽  
D. Luna ◽  
P. Llamedo ◽  
A. de la Torre
Keyword(s):  
Gravity Waves ◽  
Radio Occultation ◽  
Large Fraction ◽  
Wave Spectrum ◽  
Wave Activity ◽  
Andes Mountains ◽  
Mountain Waves ◽  
Gps Radio Occultation ◽  
The North ◽  
The One

Abstract. We first study the seasonal and geographical behavior of gravity wave activity in the lower stratosphere over the southernmost Andes mountains and their prolongation in the Antarctic Peninsula by global positioning system (GPS) radio occultation (RO) temperature profiles, obtained between years 2002 and 2005 by the CHAllenging Minisatellite Payload (CHAMP) mission. The observed features complement observations in the same zone by other satellite passive remote sensing instruments, which are able to detect different height regions and other spectral intervals of the wave spectrum. Comparisons with previous GPS RO studies in smaller areas than the one covered in our analysis are also established. Significant seasonal variation of wave activity is observed in our work, in agreement with results from other instruments. The locations of significant cases indicate that topography is an important source. Some strong wave activity is also found over open ocean. Critical level filtering is shown to have an attenuation effect, implying that a large fraction of the observed activity can be considered to be an outcome of mountain waves. The studied region has a significant advantage as compared to other regions of our planet: it generates wavefronts nearly aligned with the North-South direction (almost parallel to the mountains), whereby this geometry favors the wave detection by the nearly meridional line of sight characterizing most of the GPS RO observations used. A distribution of the observed gravity waves in terms of amplitudes and wavelengths is also presented.

Stratospheric mountain waves trailing across northern Europe

2021 ◽  
Author(s):  
Andreas Dörnbrack
Keyword(s):  
Gravity Waves ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Polar Front ◽  
Northern Europe ◽  
Polar Night ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves ◽  
Almost All

<table><tbody><tr><td> <p><span>Planetary waves disturbed the hitherto stable Arctic stratospheric polar vortex mid of<br>January 2016 in such a way that unique tropospheric and stratospheric flow conditions<br>for vertically and horizontally propagating mountain waves developed. Co-existing<br>strong low-level westerly winds across almost all European mountain ranges plus the<br>almost zonally-aligned polar front jet created these favorable conditions for deeply<br>propagating gravity waves. Furthermore, the northward displacement of the polar night<br>jet resulted in a wide-spread coverage of stratospheric mountain waves trailling across<br>northern Europe. This paper describes the particular meteorological setting by<br>analyzing the tropospheric and stratospheric flows based on the ERA5 data. The<br>potential of the flow for exciting internal gravity waves from non-orographic sources is<br>evaluated across all altitudes by considering various instability indices as δ , Ro, Ro ζ , Ro<sub>⊥</sub> ,<br>and Δ NBE</span><span>. </span></p> <p><span>The analyzed gravity waves are described and characterized in terms of<br>commonly used parameters. The main finding of this case study is the exceptionally<br>vast extension of the mountain waves trailing to high latitudes originating from the flow<br>across the mountainous sources that are located at about 45 N. As a useful addition to<br>the case study, tracks for potential research flights are proposed that sample the<br>waves by a vertically pointing airborne remote-sensing instrument. Benefits and<br>drawbacks of the different approaches to observe the meridional focussing of the<br>mountain waves into the polar night jet are discussed.</span></p> </td> </tr></tbody></table><p> </p>

scholarly journals GPS Radio Occultation Data Assimilation in the AREM Regional Numerical Weather Prediction Model for Flood Forecasts

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Wei Cheng ◽  
Youping Xu ◽  
Zhiwu Deng ◽  
Chunli Gu
Keyword(s):  
Data Assimilation ◽  
Radio Occultation ◽  
Weather Prediction ◽  
Radiosonde Data ◽  
Light Rain ◽  
Gps Radio Occultation ◽  
Study Results ◽  
Occultation Data ◽  
Radio Occultation Data

Based on the Backward Four-Dimensional Variational Data Assimilation (Backward-4DVar) system with the Advanced Regional Eta-coordinate Model (AREM), which is capable of assimilating radio occultation data, a heavy rainfall case study is performed using GPS radio occultation (GPS RO) data and routine GTS data on July 5, 2007. The case study results indicate that the use of radio occultation data after quality control can improve the quality of the analysis to be similar to that of the observations and, thus, have a positive effect when improving 24-hour rainfall forecasts. Batch tests for 119 days from May to August during the flood season in 2009 show that only the use of GPS RO data can make positive improvements in both 24-hour and 48-hour regional rainfall forecasts and obtain a better B score for 24-hour forecasts and better TS score for 48-hour forecasts. When using radio occultation refractivity data and conventional radiosonde data, the results indicate that radio occultation refractivity data can achieve a better performance for 48-hour forecasts of light rain and heavy rain.

scholarly journals Analysis of vertical wave number spectrum of atmospheric gravity waves in the stratosphere using COSMIC GPS radio occultation data

2011 ◽  
Vol 4 (8) ◽  
pp. 1627-1636 ◽  
Author(s):  
T. Tsuda ◽  
X. Lin ◽  
H. Hayashi ◽  
Keyword(s):  
Gravity Waves ◽  
Radio Occultation ◽  
Temperature Fluctuations ◽  
Ground Level ◽  
Wave Number ◽  
Radiosonde Data ◽  
Small Scale ◽  
Vertical Resolution ◽  
Full Spectrum ◽  
Gps Radio Occultation

Abstract. GPS radio occultation (RO) is characterized by high accuracy and excellent height resolution, which has great advantages in analyzing atmospheric structures including small-scale vertical fluctuations. The vertical resolution of the geometrical optics (GO) method in the stratosphere is about 1.5 km due to Fresnel radius limitations, but full spectrum inversion (FSI) can provide superior resolutions. We applied FSI to COSMIC GPS-RO profiles from ground level up to 30 km altitude, although basic retrieval at UCAR/CDAAC sets the sewing height from GO to FSI below the tropopause. We validated FSI temperature profiles with routine high-resolution radiosonde data in Malaysia and North America collected within 400 km and about 30 min of the GPS RO events. The average discrepancy at 10–30 km altitude was less than 0.5 K, and the bias was equivalent with the GO results. Using the FSI results, we analyzed the vertical wave number spectrum of normalized temperature fluctuations in the stratosphere at 20–30 km altitude, which exhibits good consistency with the model spectra of saturated gravity waves. We investigated the white noise floor that tends to appear at high wave numbers, and the substantial vertical resolution of the FSI method was estimated as about 100–200 m in the lower stratosphere. We also examined a criterion for the upper limit of the FSI profiles, beyond which bending angle perturbations due to system noises, etc., could exceed atmospheric excess phase fluctuations. We found that the FSI profiles can be used up to about 28 km in studies of temperature fluctuations with vertical wave lengths as short as 0.5 km.

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