ORCID Profile
0000-0002-9790-8546
Current Organisations
Madurai kamaraj university
,
KNMI
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Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-5804
Abstract: An accurate estimation of the Thermospheric Neutral Density (TND) is important for predicting the orbit of satellites and objects, for ex le, those with the altitude of less than 1000 km. Models are often used to simulate TNDs but their accuracy is limited due to uncertainties. Satellite missions such as CHAMP, GRACE, GOCE, Swarm, and GRACE-FO or the Satellite Laser Ranging (SLR) missions can be used to estimate along-track TNDs. However, spatial and temporal coverage of these space borne TNDs is restricted to the mission design. To make the best use of the modelling tools and measurements, we applied these along-track TND measurements within the sequential Calibration and Data Assimilation (C/DA) framework proposed by (Forootan et al., 2022, doi:10.1038/s41598-022-05952-y). The C/DA is used to re-calibrate the NRLMSISE00 model, which is called & #8220 C/DA-NRLMSISE00& #8221 , whose outputs fit well to the introduced space-borne TNDs. The C/DA-NRLMSISE00 is applicable for forecasting TNDs and in idual neutral mass compositions at any predefined vertical level (between ~100 and ~600 km) with user-defined spatial-temporal s ling. Seven periods (between 2003 - 2020) with considerable geomagnetic activity are selected for our investigations because most of the available models lack accuracy to provide reasonable TND simulations. Independent comparisons are performed with the space-borne TNDs that were not used within the C/DA framework, as well as with the outputs of other thermospheric models such as Jacchia-Bowman 2008 (JB2008) and the High Accuracy Satellite Drag Model (HASDM) database. The numerical results indicate that indeed the new model is suitable for producing multi-level global thermospheric neutral density fields.
Publisher: American Geophysical Union (AGU)
Date: 05-09-2020
DOI: 10.1029/2020GL089339
Abstract: This study explores intra‐annual oscillations (IAOs) in upper thermospheric winds using GOCE cross‐track wind measurements between 70°S and 70°N. Due to the Sun‐synchronous dawn‐dusk orbit of GOCE, the cross‐contamination between seasonality and local time variations in winds is minimal, which makes it a unique space‐based data set to extract IAOs and study their latitudinal variation. Our analysis reveals that the annual (AO), semiannual (SAO), and terannual (TAO) oscillations are robust features in thermospheric winds. The AO is strongest at middle latitudes SAO and TAO litudes increase with increasing latitude. The latitudinally averaged litudes of the AO, SAO, and TAO for dusk/dawn are 30.0/35.0, 8.5/11.3, and 6.0/6.6 m/s, respectively. The phase of AO reverses around the equator. SAO and TAO phases vary with latitude but do not reverse like the AO. For both the SAO and TAO, the average phase at dusk and dawn differs by ∼ 30 days.
Publisher: Springer Science and Business Media LLC
Date: 30-05-2020
Publisher: Springer Science and Business Media LLC
Date: 09-05-2017
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019JA027188
Abstract: We present an empirical model of thermospheric winds (High‐latitude Thermospheric Wind Model [HL‐TWiM]) that specifies F region high‐latitude horizontal neutral winds as a function of day of year, latitude, longitude, local time, and geomagnetic activity. HL‐TWiM represents the large‐scale neutral wind circulation, in geomagnetic coordinates, for the given input conditions. The model synthesizes the most extensive collection to date of historical high‐latitude wind measurements it is based on statistical analyses of several decades of F region thermospheric wind measurements from 21 ground‐based stations (Fabry‐Perot Interferometers and Scanning Doppler Imaging Fabry‐Perot Interferometers) located at various northern and southern high latitudes and two space‐based instruments (UARS WINDII and GOCE). The geomagnetic latitude and local time dependences in HL‐TWiM are represented using vector spherical harmonics, day of year and longitude variations are represented using simple harmonic functions, and the geomagnetic activity dependence is represented using quadratic B splines. In this paper, we describe the HL‐TWiM formulation and fitting procedures, and we verify the model against the neutral wind databases used in its formulation. HL‐TWiM provides a necessary benchmark for validating new wind observations and tuning our physical understanding of complex wind behaviors. Results show stronger Universal Time variation in winds at southern than northern high latitudes. Model‐data intra‐annual comparisons in this study show semiannual oscillation‐like behavior of GOCE winds, rarely observed before in wind data.
Publisher: Copernicus GmbH
Date: 24-08-2022
DOI: 10.5194/IAG-COMM4-2022-44
Abstract: & & An accurate estimation of the Thermospheric Neutral Density (TND) is important for predicting the orbit of satellites and objects, for ex le, those with the altitude of less than 1000 km. Models are often used to simulate TNDs but their accuracy is limited due to modelling restrictions and sensitivity to the calibration period. Satellite missions such as CHAMP, GRACE, GOCE, Swarm, and GRACE-FO are equipped with on-board accelerometer sensors to measure drag forces, which can be used to estimate along-track TNDs. However, spatial and temporal coverage of these space borne TNDs is restricted to the mission design. To make the best use of the modelling tools and measurements, we applied these along-track TND measurements within the sequential Calibration and Data Assimilation (C/DA) framework proposed by (Forootan et al., 2022, doi:10.1038/s41598-022-05952-y). The C/DA is used to re-calibrate the NRLMSISE00 model, which is called & #8220 C/DA-NRLMSISE00& #8221 , whose outputs fit well to the introduced space-borne TNDs. The C/DA-NRLMSISE00 is applicable for forecasting TNDs and in idual neutral mass compositions at any predefined vertical level (between ~100 and ~600 km) with user-defined spatial-temporal s ling. Nine time periods (October 2003, July 2004, March 2008, April 2010, March 2015, September 2017, August 2018, September 2020 and October 2021) associated with space weather storms are selected for our investigations because most of the available models lack accuracy to provide reasonable TND simulations. Independent comparisons are performed with the space-borne TNDs that were not used within the C/DA framework, as well as with the outputs of other thermospheric models such as Jacchia-Bowman 2008 (JB2008) and the High Accuracy Satellite Drag Model (HASDM) database. The numerical results indicate improvements in the Root Mean Squared Errors (RMSE) of the C/DA-NRLMSISE00's TND forecasts compared to NRLMSISE-00, JB2008 and HASDM along-track of the LEO missions. The percentage reductions are found to be: 51%, 8% and 8 % along GRACE (2003, average altitude 490 km), 25%, 20% and 48% along GOCE (2010, average altitude 270 km), 46%, 37% and 35% along Swarm B (2015, average altitude 520 km), 54%, 12% and 5 % along Swarm B (2017, average altitude 514 km), and 41% and 64% along GRACE (FO) (2021, average altitude 504 km), respectively.& &
No related grants have been discovered for Eelco Doornbos.