scholarly journals Preliminary signs of the initiation of deep convection by GNSS

2012 ◽  
Vol 12 (8) ◽  
pp. 20351-20382
Author(s):  
H. Brenot ◽  
J. Neméghaire ◽  
L. Delobbe ◽  
N. Clerbaux ◽  
M. Van Roozendael
Keyword(s):  
Deep Convection ◽  
Critical Role ◽  
Small Scale ◽  
Convective System ◽  
Weather Forecasts ◽  
Convective Systems ◽  
Infrared Radiance ◽  
Using Data ◽  
Convective Cells

Abstract. This study reports on the exploitation of GNSS for weather forecasts, especially for nowcasting. We focus on GPS observations (post-processing with a time resolution of 15 min) and try to establish typical configurations of the humidity field which characterise convective systems and particularly which supply forerunners of their initiation associated with deep convection. We show the critical role of GNSS horizontal gradients of humidity to detect small scale structures of the troposphere (i.e. convective cells), and then we present our strategy to obtain typical water vapour configurations by GNSS, called "H2O alert". These alerts are based on a dry/wet contrast taking place during a 30 min window before initiation of a convective system. GNSS observations have been assessed for the rainfall event of the 28–29 June 2005 using data from the Belgian dense network (baseline from 5 to 30 km). To validate our GNSS H2O alert, we use the detection of precipitation by C-band weather radar and thermal infrared radiance of the 10.8-μm channel [Ch09] of SEVIRI instrument on METEOSAT Second Generation. Our H2O alert obtains a score of about 80%.

scholarly journals Preliminary signs of the initiation of deep convection by GNSS

2013 ◽  
Vol 13 (11) ◽  
pp. 5425-5449 ◽  
Author(s):  
H. Brenot ◽  
J. Neméghaire ◽  
L. Delobbe ◽  
N. Clerbaux ◽  
P. De Meutter ◽  
...  
Keyword(s):  
Water Vapour ◽  
Time Resolution ◽  
Time Window ◽  
Deep Convection ◽  
Critical Role ◽  
Small Scale ◽  
Convective System ◽  
International Gnss Service ◽  
Total Delay ◽  
Water Vapour Content

Abstract. This study reports on the exploitation of GNSS (Global Navigation Satellite System) and a new potential application for weather forecasts and nowcasting. We focus on GPS observations (post-processing with a time resolution of 5 and 15 min and fast calculations with a time resolution of 5 min) and try to establish typical configurations of the water vapour field which characterise convective systems and particularly which supply precursors of their initiation are associated with deep convection. We show the critical role of GNSS horizontal gradients of the water vapour content to detect small scale structures of the troposphere (i. e. convective cells), and then we present our strategy to obtain typical water vapour configurations by GNSS called "H2O alert". These alerts are based on a dry/wet contrast taking place during a 30 min time window before the initiation of a convective system. GNSS observations have been assessed for the rainfall event of 28–29 June 2005 using data from the Belgian dense network (baseline from 5 to 30 km). To validate our GNSS H2O alerts, we use the detection of precipitation by C-band weather radar and thermal infrared radiance (cloud top temperature) of the 10.8-micrometers channel [Ch09] of SEVIRI instrument on Meteosat Second Generation. Using post-processed measurements, our H2O alerts obtain a score of about 80%. Final and ultra-rapid IGS (International GNSS Service) orbits have been tested and show equivalent results. Fast calculations (less than 10 min) have been processed for 29 June 2005 with a time resolution of 5 min. The mean bias (and standard deviation) between fast and reference post-processed ZTD (zenith total delay) and gradients are, respectively, 0.002 (± 0.008) m and 0.001 (± 0.004) m. The score obtained for the H2O alerts generated by fast calculations is 65%.

Impact of the Korea Rapid Developing Thunderstorms (K-RDT) product nudging to the convective parameterization over the Korean Peninsula

2020 ◽  
Author(s):  
Namgu Yeo ◽  
Eun-Chul Chang ◽  
Ki-Hong Min
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Deep Convection ◽  
Weather Prediction ◽  
Model System ◽  
Prediction Skill ◽  
Precipitation Forecast ◽  
Small Scale ◽  
Convective System ◽  
Convective Cells

<p>In this study, Korea Rapid Developing Thunderstorms (K-RDT) product from geostationary meteorological satellite which represents developing stage of convective cells is nudged to the Simplified Arakawa Schubert (SAS) deep convection scheme using a simple nudging technique in order to improve prediction skill of a heavy rainfall caused by mesoscale convective system over South Korea in the short-term forecast. Impact of the K-RDT information is investigated on the Global/Regional Integrated Model system (GRIMs) regional model program (RMP) system. For the selected heavy rainfall cases, the control run without nudging and two nudging experiments with different nudging period are performed. Although the simulated precipitations in the nudging experiments tend to depend on the distribution of convective cells detected in the K-RDT algorithm, the nudging experiment shows improved precipitation forecast than the control experiment. Particularly, the experiment with nudging for longer time produces better prediction skill. The results present that the small-scale convective cells from the K-RDT which are detected with a 1-km resolution have clear impacts to large-scale atmospheric fields. Therefore, it is suggested that utilizing small-scale information of convective system in the numerical weather prediction can have critical impact to improve forecast skill when the model system, which cannot properly represent sub-grid scale convections.</p>

scholarly journals Turbulent vertical diffusivity in the sub-tropical stratosphere

2007 ◽  
Vol 7 (3) ◽  
pp. 6603-6629 ◽  
Author(s):  
I. Pisso ◽  
B. Legras
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Small Scale ◽  
Chemistry Transport Model ◽  
Weather Forecasts ◽  
Chemical Tracers ◽  
Vertical Diffusivity ◽  
Large Ensembles ◽  
Local Equivalent ◽  
Using Data

Abstract. Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and parametrized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Center for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). We have investigated cases in subtropical latitudes using data from HIBISCUS campaign. Upper bound on the vertical diffusivity is found to be of the order of 0.5 m2 s−1 in the subtropical region, which is larger than the estimates at higher latitudes. The relation between diffusion and dispersion is studied by estimating Lyapunov exponents and studying their variation according to the presence of active dynamical structures.

scholarly journals On the improvement of wave and storm surge hindcasts by downscaled atmospheric forcing: application to historical storms

2018 ◽  
Vol 18 (4) ◽  
pp. 997-1012 ◽  
Author(s):  
Émilie Bresson ◽  
Philippe Arbogast ◽  
Lotfi Aouf ◽  
Denis Paradis ◽  
Anna Kortcheva ◽  
...  
Keyword(s):  
Storm Surge ◽  
Initial Conditions ◽  
Storm Surges ◽  
Atmospheric Model ◽  
Small Scale ◽  
Severe Damage ◽  
Weather Forecasts ◽  
Whole Process ◽  
Medium Range ◽  
Using Data

Abstract. Winds, waves and storm surges can inflict severe damage in coastal areas. In order to improve preparedness for such events, a better understanding of storm-induced coastal flooding episodes is necessary. To this end, this paper highlights the use of atmospheric downscaling techniques in order to improve wave and storm surge hindcasts. The downscaling techniques used here are based on existing European Centre for Medium-Range Weather Forecasts reanalyses (ERA-20C, ERA-40 and ERA-Interim). The results show that the 10 km resolution data forcing provided by a downscaled atmospheric model gives a better wave and surge hindcast compared to using data directly from the reanalysis. Furthermore, the analysis of the most extreme mid-latitude cyclones indicates that a four-dimensional blending approach improves the whole process, as it assimilates more small-scale processes in the initial conditions. Our approach has been successfully applied to ERA-20C (the 20th century reanalysis).

scholarly journals Turbulent vertical diffusivity in the sub-tropical stratosphere

2008 ◽  
Vol 8 (3) ◽  
pp. 697-707 ◽  
Author(s):  
I. Pisso ◽  
B. Legras
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Small Scale ◽  
Weather Forecasts ◽  
Chemical Tracers ◽  
Vertical Diffusivity ◽  
Large Ensembles ◽  
Local Equivalent ◽  
Using Data

Abstract. Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and paramaterized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Centre for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). We focus on a case study in subtropical latitudes using data from HIBISCUS campaign. An upper bound on the vertical diffusivity is found in this case study to be of the order of 0.5 m2 s−1 in the subtropical region, which is larger than the estimates at higher latitudes. The relation between diffusion and dispersion is studied by estimating Lyapunov exponents and studying their variation according to the presence of active dynamical structures.

scholarly journals Backward Adaptive Brightness Temperature Threshold Technique (BAB3T): A Methodology to Determine Extreme Convective Initiation Regions Using Satellite Infrared Imagery

2020 ◽  
Vol 12 (2) ◽  
pp. 337
Author(s):  
Maite Cancelada ◽  
Paola Salio ◽  
Daniel Vila ◽  
Stephen W. Nesbitt ◽  
Luciano Vidal
Keyword(s):  
Brightness Temperature ◽  
Deep Convection ◽  
Convective System ◽  
Temperature Threshold ◽  
Lightning Flash ◽  
Convective Initiation ◽  
Convective Storms ◽  
Convective Systems ◽  
Diurnal Cycles ◽  
Backward Tracking

Thunderstorms in southeastern South America (SESA) stand out in satellite observations as being among the strongest on Earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, the prevalence for extremely tall, wide convective cores and broad stratiform regions. Accurately quantifying when and where strong convection is initiated presents great interest in operational forecasting and convective system process studies due to the relationship between convective storms and severe weather phenomena. This paper generates a novel methodology to determine convective initiation (CI) signatures associated with extreme convective systems, including extreme events. Based on the well-established area-overlapping technique, an adaptive brightness temperature threshold for identification and backward tracking with infrared data is introduced in order to better identify areas of deep convection associated with and embedded within larger cloud clusters. This is particularly important over SESA because ground-based weather radar observations are currently limited to particular areas. Extreme rain precipitation features (ERPFs) from Tropical Rainfall Measurement Mission are examined to quantify the full satellite-observed life cycle of extreme convective events, although this technique allows examination of other intense convection proxies such as the identification of overshooting tops. CI annual and diurnal cycles are analyzed and distinctive behaviors are observed for different regions over SESA. It is found that near principal mountain barriers, a bimodal diurnal CI distribution is observed denoting the existence of multiple CI triggers, while convective initiation over flat terrain has a maximum frequency in the afternoon.

scholarly journals A Numerical Study of the Beijing Extreme Rainfall of 21 July 2012 and the Impact of Topography

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Hongxiong Xu ◽  
Wenqing Yao
Keyword(s):  
Numerical Study ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Convective System ◽  
Stratiform Region ◽  
Moist Environment ◽  
The Right ◽  
Convective Cells ◽  
The Impact

The extreme rainfall on 21 July 2012 is the heaviest rainfall that has occurred in Beijing since 1961. Observations and WRF (Weather Research and Forecasting) model are used to study the effect of MCS (mesoscale convective system) and topography on the rainfall. In this high-impact event, a quasi-stationary MCS developed in a favorable moist environment. The numerical simulation successfully reproduced the amount, location, and time evolution of the rainfall despite 4–6 h delay. In particular, the model reproduced the repeat passage of convective cells at the leading convergence line region along Taihang Mountains and the trailing stratiform region, producing the rainfall at nearly the right position. Results indicate the important roles of mesolow and low-level jet in maintaining the conditional instability that lifted the moist air to trigger deep convection and the repeated initiation and movement of the line shaped convective cells that produced the rainfall. The sensitive experiment was then further carried out to examine the effect of topography on this heavy rainfall. The reduction in model elevation field significantly influenced the above mesoscale systems, which lead to convective cells becoming less organized, and the peak rainfall amount in Beijing decreased by roughly 50%.

scholarly journals Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa

2019 ◽  
Author(s):  
Samuel Nahmani ◽  
Olivier Bock ◽  
Françoise Guichard
Keyword(s):  
West Africa ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Small Scale ◽  
Strong Impact ◽  
Sampled Data ◽  
Convective Systems ◽  
Temporal Sampling ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract. This study analyzes the characteristics of GPS tropospheric estimates (Zenith Wet Delays, and 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 seasons of West Africa. This region is particularly well suited because of the high frequency of occurrence of MCSs in contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled data with the six AMMA GPS stations. Tropospheric estimates for 3-year period (2006–2008), processed with both GAMIT and GIPSY-OASIS software packages, were analyzed and inter-compared. First, the case an MCS which 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 convective cells as detected on reflectivity maps from MIT’s C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. The sensitivity is however different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of Zenith Wet Delays 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 Zenith Wet Delays 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 Zenith Wet Delays coincident with the cold-pool crossing time associated to the MCSs. The tropospheric gradients are reflecting the path of the MCS propagation (generally from East to West). This study concludes that Zenith Wet Delays, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station.

scholarly journals A case study of a derecho storm in dry, high-shear environment

Időjárás ◽  
2021 ◽  
Vol 125 (1) ◽  
pp. 1-37
Author(s):  
Zoltán Sipos ◽  
André Simon ◽  
Kálmán Csirmaz ◽  
Tünde Lemler ◽  
Robert-Daniel Manta ◽  
...  
Keyword(s):  
Wind Shear ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Cold Pool ◽  
Small Scale ◽  
Convective System ◽  
High Wind ◽  
Large Area ◽  
Wind Gusts ◽  
Lapse Rates

The present study examines the origin and environmental conditions of the severe convective windstorm on September 17, 2017, which affected several countries in the central and southeastern Europe, above all Serbia and Romania. The large area of the damage swath (at least 500 km long) and high wind gusts (up to 40 m/s) would classify this event as a derecho or at least as a storm very similar to derechos (with respect to newer definition proposals). Small-scale bow echoes were found in areas with highest reported wind gusts, and some thunderstorms within the storm-producing convective system were probably supercells. The existence of high wind shear and storm rotation could be also related to the significant rightward deflection of the system with respect to the mean wind and propagation of other thunderstorms and systems observed on that day. In contrary to many other known derecho events, this storm propagated toward a very dry airmass exhibiting only low or moderate convective available potential energy (CAPE) values. This is shown by soundings, ECMWF model outputs, and vertical profiles from the IASI L2 satellite sounder. Several convective parameters (e.g. CAPE, downdraft CAPE, derecho composite parameter, 0-3-km relative humidity, 0-6-km shear) were evaluated and compared with proximity soundings of other described European derechos or with the available climatology. The possibility of a balance between the cold pool-generated horizontal vorticity and the environmental shear is also discussed. It is concluded that identification of low-level humidity sources (with aid of storm-relative wind vectors or streamlines) can be important in forecasting of thunderstorm systems moving toward an airmass, which is seemingly too dry for development and maintenance of deep convection. It is also shown that due to low CAPE values, some composite parameters would not indicate favourable conditions for a long-lived convective system. The lack of radiosonde observations can be partially supplemented by data from the IASI L2 sounder, which profiles can be largely different from model forecasts, showing much drier air in the mid- and upper troposphere in this case. It is concluded that due to the absence of strong synoptic forcing and larger pressure gradient at surface, convective processes played major role in the windstorm development. The presence of high temperature lapse rates at low- and mid-levels, high wind shear and unusually dry pre-storm airmass could be considered as the most important signatures related to the storm severity.

scholarly journals Independent Board, Audit Committee, Risk Committee, the Meeting Attendance level and Its Impact on the Performance: A Study of Listed Banks in Indonesia

2017 ◽  
Vol 8 (3) ◽  
pp. 24 ◽  
Author(s):  
Te-Kuang Chou ◽  
Agung Dharmawan Buchdadi
Keyword(s):  
Audit Committee ◽  
Positive Impact ◽  
Critical Role ◽  
Least Square ◽  
Small Scale ◽  
Committee Meeting ◽  
Net Interest Margin ◽  
Risk Committee ◽  
Interest Margin

This study determines the effect of good corporate governance on the performance of banks in Indonesia. The variables used are independent board (IB), the annual board meeting (BM), the percentage of annual board of director meeting attendance, the annual board-executive meeting (BEM), the percentage of annual board-executive meeting attendance, audit committee (AC), audit committee meeting (ACM), the percentage of annual audit committee meeting attendance, risk committee (RC), risk committee meeting (RCM), and the percentage of annual risk committee meeting attendance. The analysis technique employed in this study is two-stage least square (2SLS) panel data regression using return on asset (ROA), net interest margin ratio (NIM), and Tobin’s Q as the proxies of bank performance. The data used are listed bank in Indonesia Capital Market between 2013 and 2015. The findings reveal that the independent board has a positive impact on net interest margin among the big scale bank. However, among the small scale bank the independent board of directors has the positive impact on the market value, but they will have the lack of information that could obstruct the accounting based profit of the bank. Moreover, the findings of this study also explain the important role of meeting attendance for the accounting based profitability of the bank. This study also found the critical role of the audit committee in the banking industry.

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