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281 results on '"Fernando, Harindra J. S."'

1. Generative Nowcasting of Marine Fog Visibility in the Grand Banks area and Sable Island in Canada

Author

Gultepe, Eren, Wang, Sen, Blomquist, Byron, Fernando, Harindra J. S., Kreidl, O. Patrick, Delene, David J., and Gultepe, Ismail

Subjects
Computer Science - Machine Learning, Physics - Atmospheric and Oceanic Physics
Abstract

This study presents the application of generative deep learning techniques to evaluate marine fog visibility nowcasting using the FATIMA (Fog and turbulence interactions in the marine atmosphere) campaign observations collected during July 2022 in the North Atlantic in the Grand Banks area and vicinity of Sable Island (SI), northeast of Canada. The measurements were collected using the Vaisala Forward Scatter Sensor model FD70 and Weather Transmitter model WXT50, and Gill R3A ultrasonic anemometer mounted on the Research Vessel Atlantic Condor. To perform nowcasting, the time series of fog visibility (Vis), wind speed, dew point depression, and relative humidity with respect to water were preprocessed to have lagged time step features. Generative nowcasting of Vis time series for lead times of 30 and 60 minutes were performed using conditional generative adversarial networks (cGAN) regression at visibility thresholds of Vis < 1 km and < 10 km. Extreme gradient boosting (XGBoost) was used as a baseline method for comparison against cGAN. At the 30 min lead time, Vis was best predicted with cGAN at Vis < 1 km (RMSE = 0.151 km) and with XGBoost at Vis < 10 km (RMSE = 2.821 km). At the 60 min lead time, Vis was best predicted with XGBoost at Vis < 1 km (RMSE = 0.167 km) and Vis < 10 km (RMSE = 3.508 km), but the cGAN RMSE was similar to XGBoost. Despite nowcasting Vis at 30 min being quite difficult, the ability of the cGAN model to track the variation in Vis at 1 km suggests that there is potential for generative analysis of marine fog visibility using observational meteorological parameters.

Published
2024

6. Preparing Scientists, Policy-Makers, and Managers for a Fast-Forward Future

Author

Norgaard, Richard B., Wiens, John A., Brandt, Stephen B., Canuel, Elizabeth A, Collier, Tracy K., Dale, Virginia H., Fernando, Harindra J. S., Holzer, Thomas L., Luoma, Samuel N., and Resh, Vincent H.

Subjects
California, climate change, ecology, environmental change, Sacramento-San Joaquin Delta, thresholds, uncertainty, policy, rapid change, governance
Abstract

Ecosystems in the Sacramento–San Joaquin Delta are changing rapidly, as are ecosystems around the world. Extreme events are becoming more frequent and thresholds are likely to be crossed more often, creating greater uncertainty about future conditions. The accelerating speed of change means that ecological systems may not remain stable long enough for scientists to understand them, much less use their research findings to inform policy and management. Faced with these challenges, those involved in science, policy, and management must adapt and change and anticipate what the ecosystems may be like in the future. We highlight several ways of looking ahead—scenario analyses, horizon scanning, expert elicitation, and dynamic planning—and suggest that recent advances in distributional ecology, disturbance ecology, resilience thinking, and our increased understanding of coupled human–natural systems may provide fresh ways of thinking about more rapid change in the future. To accelerate forward-looking science, policy, and management in the Delta, we propose that the State of California create a Delta Science Visioning Process to fully and openly assess the challenges of more rapid change to science, policy, and management and propose appropriate solutions, through legislation, if needed.

Published
2021

8. On the Power-law Scaling of Turbulence Cospectra Part 1: Stably Stratified Atmospheric Boundary Layer

Author

Cheng, Yu, Li, Qi, Grachev, Andrey, Argentini, Stefania, Fernando, Harindra J. S., and Gentine, Pierre

Subjects
Physics - Atmospheric and Oceanic Physics, Physics - Fluid Dynamics
Abstract

Turbulent fluxes in the atmospheric surface layer are key input for the prediction of weather, hydrology, and carbon dioxide concentration. In numerical modelling of turbulent fluxes, a -7/3 power-law scaling in turbulence cospectra is usually assumed at high wavenumbers. In eddy-covariance (EC) measurements of turbulent fluxes, an assumed shape of turbulence cospectra is typically required for high-frequency spectral corrections, typically assuming a -7/3 power law. The derivation of -7/3 power-law scaling is based primarily on dimensional analysis, and other cospectral scaling has also been observed. Here we examine the shape of turbulence cospectra at high wavenumbers from extensive field measurements of wind velocity, temperature, water vapour and CO2 concentrations in various stably stratified atmospheric conditions. We propose a turbulence cospectral shape with -2 power law rather than -7/3 law for high wavenumber equilibrium range of the stable atmospheric boundary layer. This finding contributes to improved estimation of turbulent fluxes in both modelling and observation., Comment: 21 pages, 15 figures

Published
2018

9. Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Author

Shroyer, Emily, Tandon, Amit, Sengupta, Debasis, Fernando, Harindra J. S., Lucas, Andrew J., Farrar, J. Thomas, Chattopadhyay, Rajib, de Szoeke, Simon, Flatau, Maria, Rydbeck, Adam, Wijesekera, Hemantha, McPhaden, Michael, Seo, Hyodae, Subramanian, Aneesh, Venkatesan, R, Joseph, Jossia, Ramsundaram, S., Gordon, Arnold L., Bohman, Shannon M., Pérez, Jaynise, Simoes-Sousa, Iury T., Jayne, Steven R., Todd, Robert E., Bhat, G. S., Lankhorst, Matthias, Schlosser, Tamara, Adams, Katherine, Jinadasa, S. U. P, Mathur, Manikandan, Mohapatra, M., Rao, E. Pattabhi Rama, Sahai, A. K., Sharma, Rashmi, Lee, Craig, Rainville, Luc, Cherian, Deepak, Cullen, Kerstin, Centurioni, Luca R., Hormann, Verena, MacKinnon, Jennifer, Send, Uwe, Anutaliya, Arachaporn, Waterhouse, Amy, Black, Garrett S., Dehart, Jeremy A., Woods, Kaitlyn M., Creegan, Edward, Levy, Gad, Kantha, Lakshmi H., and Subrahmanyam, Bulusu

Published
2021

17. Structure of Turbulence in Katabatic Flows below and above the Wind-Speed Maximum

Author

Grachev, Andrey A., Leo, Laura S., Di Sabatino, Silvana, Fernando, Harindra J. S., Pardyjak, Eric R., and Fairall, Christopher W.

Subjects
Physics - Atmospheric and Oceanic Physics
Abstract

Measurements of small-scale turbulence made over the complex-terrain atmospheric boundary layer during the MATERHORN Program are used to describe the structure of turbulence in katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels at four towers deployed along the East lower slope (2-4 deg) of Granite Mountain. The multi-level observations made during a 30-day long MATERHORN-Fall field campaign in September-October 2012 allowed studying of temporal and spatial structure of katabatic flows in detail, and herein we report turbulence and their variations in katabatic winds. Observed vertical profiles show steep gradients near the surface, but in the layer above the slope jet the vertical variability is smaller. It is found that the vertical (normal to the slope) momentum flux and horizontal (along the slope) heat flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed downward (upward) whereas the horizontal heat flux is downslope (upslope) below (above) the wind maximum. Our study therefore suggests that the position of the jet-speed maximum can be obtained by linear interpolation between positive and negative values of the momentum flux (or the horizontal heat flux) to derive the height where flux becomes zero. It is shown that the standard deviations of all wind speed components (therefore the turbulent kinetic energy) and the dissipation rate of turbulent kinetic energy have a local minimum, whereas the standard deviation of air temperature has an absolute maximum at the height of wind-speed maximum. We report several cases where the vertical and horizontal heat fluxes are compensated. Turbulence above the wind-speed maximum is decoupled from the surface, and follows the classical local z-less predictions for stably stratified boundary layer., Comment: Manuscript submitted to Boundary-Layer Meteorology (05 December 2014)

Published
2015
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18. The Sundowner Winds Experiment (SWEX) in Santa Barbara, California: Advancing Understanding and Predictability of Downslope Windstorms in Coastal Environments

Author

Carvalho, Leila M. V., primary, Duine, Gert-Jan, additional, Clements, Craig, additional, De Wekker, Stephan F. J., additional, Fernando, Harindra J. S., additional, Fitzjarrald, David R., additional, Fovell, Robert G., additional, Jones, Charles, additional, Wang, Zhien, additional, White, Loren, additional, Bucholtz, Anthony, additional, Brewer, Matthew J., additional, Brown, William, additional, Burkhart, Matt, additional, Creegan, Edward, additional, Deng, Min, additional, de Orla-Barile, Marian, additional, Emmitt, David, additional, Greco, Steve, additional, Hock, Terry, additional, Kasic, James, additional, Malarkey, Kiera, additional, Modjeski, Griffin, additional, Oncley, Steven, additional, Rockwell, Alison, additional, Seto, Daisuke, additional, Thompson, Callum, additional, and Vömel, Holger, additional

Published
2024
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20. THE SECOND WIND FORECAST IMPROVEMENT PROJECT (WFIP2) : Observational Field Campaign

Author

Wilczak, James M., Stoelinga, Mark, Berg, Larry K., Sharp, Justin, Draxl, Caroline, McCaffrey, Katherine, Banta, Robert M., Bianco, Laura, Djalalova, Irina, Lundquist, Julie K., Muradyan, Paytsar, Choukulkar, Aditya, Leo, Laura, Bonin, Timothy, Pichugina, Yelena, Eckman, Richard, Long, Charles N., Lantz, Kathleen, Worsnop, Rochelle P., Bickford, Jim, Bodini, Nicola, Chand, Duli, Clifton, Andrew, Cline, Joel, Cook, David R., Fernando, Harindra J. S., Friedrich, Katja, Krishnamurthy, Raghavendra, Marquis, Melinda, McCaa, Jim, Olson, Joseph B., Otarola-Bustos, Sebastian, Scott, George, Shaw, William J., Wharton, Sonia, and White, Allen B.

Published
2019

25. A mechanism for coastal fog genesis at evening transition.

Author

Hintz, Thomas J., Huang, Kelly Y., Hoch, Sebastian W., Bardoel, Stef L., Gaberšek, Saša, Gultepe, Ismail, Ruiz‐Plancarte, Jesus, Pardyjak, Eric R., Wang, Qing, and Fernando, Harindra J. S.

Subjects
ATMOSPHERIC boundary layer, BOUNDARY layer (Aerodynamics), TURBULENCE, ISLANDS, ACQUISITION of data
Abstract

Transitional changes in the atmospheric boundary layer (ABL) are known to facilitate the onset of terrestrial fog, which is defined as a condition with near‐surface visibility <1 km due to airborne water droplets. In particular, the evening transition from a daytime convective ABL to a night‐time stable ABL provides favorable conditions for fog. This article describes a local fog event observed during the evening transition at a Canadian islet in the north Atlantic known as Sable Island during the "Fog and Turbulence Interactions in the Marine Atmosphere (Fatima)" field campaign. The comprehensive set of data collected using a myriad of instruments covering a wide range of scales allowed identification of a novel mechanism underlying this fog event. Therein an ocean–land discontinuity created a flow regime consisting of several stacked boundary layers, interplay of which produced a thin low‐level cloud that then diffused downward to the surface, causing visibility reduction. This mechanism offers useful insights on the role of boundary layers, stratification, and turbulence in fog genesis over oceanic islands. [ABSTRACT FROM AUTHOR]

Published
2024
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26. Measurements and Model Improvement: Insight into NWP Model Error Using Doppler Lidar and Other WFIP2 Measurement Systems

Author

Banta, Robert M., primary, Pichugina, Yelena L., additional, Brewer, W. Alan, additional, Balmes, Kelly A., additional, Adler, Bianca, additional, Sedlar, Joseph, additional, Darby, Lisa S., additional, Turner, David D., additional, Kenyon, Jaymes S., additional, Strobach, Edward J., additional, Carroll, Brian J., additional, Sharp, Justin, additional, Stoelinga, Mark T., additional, Cline, Joel, additional, and Fernando, Harindra J. S., additional

Published
2023
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31. Fog Intermittency and Critical Behavior

Author

Huang, Kelly Y., primary, Katul, Gabriel G., additional, Hintz, Thomas J., additional, Ruiz-Plancarte, Jesus, additional, Wang, Qing, additional, and Fernando, Harindra J. S., additional

Published
2023
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32. ASIRI : An Ocean–Atmosphere Initiative for Bay of Bengal

Author

Wijesekera, Hemantha W., Shroyer, Emily, Tandon, Amit, Ravichandran, M., Sengupta, Debasis, Jinadasa, S. U. P., Fernando, Harindra J. S., Agrawal, Neeraj, Arulananthan, K., Bhat, G. S., Baumgartner, Mark, Buckley, Jared, Centurioni, Luca, Conry, Patrick, Farrar, J. Thomas, Gordon, Arnold L., Hormann, Verena, Jarosz, Ewa, Jensen, Tommy G., Johnston, Shaun, Lankhorst, Matthias, Lee, Craig M., Leo, Laura S., Lozovatsky, Iossif, Lucas, Andrew J., Mackinnon, Jennifer, Mahadevan, Amala, Nash, Jonathan, Omand, Melissa M., Pham, Hieu, Pinkel, Robert, Rainville, Luc, Ramachandran, Sanjiv, Rudnick, Daniel L., Sarkar, Sutanu, Send, Uwe, Sharma, Rashmi, Simmons, Harper, Stafford, Kathleen M., St. Laurent, Louis, Venayagamoorthy, Karan, Venkatesan, Ramasamy, Teague, William J., Wang, David W., Waterhouse, Amy F., Weller, Robert, and Whalen, Caitlin B.

Published
2016

43. Bay of Bengal intraseasonal oscillations and the 2018 monsoon onset

Author

Shroyer, Emily L., Tandon, Amit, Sengupta, Debasis, Fernando, Harindra J. S., Lucas, Andrew J., Farrar, J. Thomas, Chattopadhyay, Rajib, de Szoeke, Simon P., Flatau, Maria, Rydbeck, Adam, Wijesekera, Hemantha W., McPhaden, Michael J., Seo, Hyodae, Subramanian, Aneesh C., Venkatesan, Ramasamy, Joseph, Jossia K., Ramsundaram, S., Gordon, Arnold L., Bohman, Shannon M., Pérez, Jaynise, Simoes-Sousa, Iury T., Jayne, Steven R., Todd, Robert E., Bhat, G. S., Lankhorst, Matthias, Schlosser, Tamara L., Adams, Katherine, Jinadasa, S. U. P., Mathur, Manikandan, Mohapatra, Mrutyunjay, Rama Rao, E. Pattabhi, Sahai, Atul Kumar, Sharma, Rashmi, Lee, Craig, Rainville, Luc, Cherian, Deepak A., Cullen, Kerstin, Centurioni, Luca R., Hormann, Verena, MacKinnon, Jennifer A., Send, Uwe, Anutaliya, Arachaporn, Waterhouse, Amy F., Black, Garrett S., Dehart, Jeremy A., Woods, Kaitlyn M., Creegan, Edward, Levy, Gad, Kantha, Lakshmi, Subrahmanyam, Bulusu, Shroyer, Emily L., Tandon, Amit, Sengupta, Debasis, Fernando, Harindra J. S., Lucas, Andrew J., Farrar, J. Thomas, Chattopadhyay, Rajib, de Szoeke, Simon P., Flatau, Maria, Rydbeck, Adam, Wijesekera, Hemantha W., McPhaden, Michael J., Seo, Hyodae, Subramanian, Aneesh C., Venkatesan, Ramasamy, Joseph, Jossia K., Ramsundaram, S., Gordon, Arnold L., Bohman, Shannon M., Pérez, Jaynise, Simoes-Sousa, Iury T., Jayne, Steven R., Todd, Robert E., Bhat, G. S., Lankhorst, Matthias, Schlosser, Tamara L., Adams, Katherine, Jinadasa, S. U. P., Mathur, Manikandan, Mohapatra, Mrutyunjay, Rama Rao, E. Pattabhi, Sahai, Atul Kumar, Sharma, Rashmi, Lee, Craig, Rainville, Luc, Cherian, Deepak A., Cullen, Kerstin, Centurioni, Luca R., Hormann, Verena, MacKinnon, Jennifer A., Send, Uwe, Anutaliya, Arachaporn, Waterhouse, Amy F., Black, Garrett S., Dehart, Jeremy A., Woods, Kaitlyn M., Creegan, Edward, Levy, Gad, Kantha, Lakshmi, and Subrahmanyam, Bulusu

Abstract

Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 102(10), (2021): E1936–E1951, https://doi.org/10.1175/BAMS-D-20-0113.1., In the Bay of Bengal, the warm, dry boreal spring concludes with the onset of the summer monsoon and accompanying southwesterly winds, heavy rains, and variable air–sea fluxes. Here, we summarize the 2018 monsoon onset using observations collected through the multinational Monsoon Intraseasonal Oscillations in the Bay of Bengal (MISO-BoB) program between the United States, India, and Sri Lanka. MISO-BoB aims to improve understanding of monsoon intraseasonal variability, and the 2018 field effort captured the coupled air–sea response during a transition from active-to-break conditions in the central BoB. The active phase of the ∼20-day research cruise was characterized by warm sea surface temperature (SST > 30°C), cold atmospheric outflows with intermittent heavy rainfall, and increasing winds (from 2 to 15 m s−1). Accumulated rainfall exceeded 200 mm with 90% of precipitation occurring during the first week. The following break period was both dry and clear, with persistent 10–12 m s−1 wind and evaporation of 0.2 mm h−1. The evolving environmental state included a deepening ocean mixed layer (from ∼20 to 50 m), cooling SST (by ∼1°C), and warming/drying of the lower to midtroposphere. Local atmospheric development was consistent with phasing of the large-scale intraseasonal oscillation. The upper ocean stores significant heat in the BoB, enough to maintain SST above 29°C despite cooling by surface fluxes and ocean mixing. Comparison with reanalysis indicates biases in air–sea fluxes, which may be related to overly cool prescribed SST. Resolution of such biases offers a path toward improved forecasting of transition periods in the monsoon., This work was supported through the U.S. Office of Naval Research’s Departmental Research Initiative: Monsoon Intraseasonal Oscillations in the Bay of Bengal, the Indian Ministry of Earth Science’s Ocean Mixing and Monsoons Program, and the Sri Lankan National Aquatic Resources Research and Development Agency. We thank the Captain and crew of the R/V Thompson for their help in data collection. Surface atmospheric fields included fluxes were quality controlled and processed by the Boundary Layer Observations and Processes Team within the NOAA Physical Sciences Laboratory. Forecast analysis was completed by India Meteorological Department. Drone image was taken by Shreyas Kamat with annotations by Gualtiero Spiro Jaeger. We also recognize the numerous researchers who supported cruise- and land-based measurements. This work represents Lamont-Doherty Earth Observatory contribution number 8503, and PMEL contribution number 5193., 2022-04-01

Published
2022

49. Observations of Stably Stratified Flow through a Microscale Gap

Author

Vassallo, Daniel, Krishnamurthy, Raghavendra, Menke, Robert, Fernando, Harindra J. S., Vassallo, Daniel, Krishnamurthy, Raghavendra, Menke, Robert, and Fernando, Harindra J. S.

Abstract

This paper reports the findings of a comprehensive field investigation on flow through a mountain gap subject to a range of stably stratified environmental conditions. This study was embedded within the Perdigão field campaign, which was conducted in a region of parallel double-ridge topography with ridge-normal wind climatology. One of the ridges has a well-defined gap (col) at the top, and an array of in situ and remote sensors, including a novel triple Doppler lidar system, was deployed around it. The experimental design was mostly guided by previous numerical and theoretical studies conducted with an idealized configuration where a flow (with characteristic velocity U0 and buoyancy frequency N) approaches normal to a mountain of height h with a gap at its crest, for which the governing parameters are the dimensionless mountain height G = 0 and various gap aspect ratios. Modified formsof G were proposed to account for real-world atmospheric variability, andthe results are discussed in terms of a gap-averaged value Gc. The nature ofgap flow was highly dependent on Gc, wherein a nearly neutral flow regime (Gc< 1), a transitional mountain wave regime (Gc ∼ O(1)), and a gap-jettingregime (Gc > O(1)) were identified. The measurements were in broad agreement with previous numerical and theoretical studies on a single ridge with agap or double ridge topography, although details vary. This is the first ever detailed field study reported on microscale (O(100 m))gap flows, and providesuseful data and insights for future theoretical and numerical studies.

Published
2021

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