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https://doi.org/10.5194/egusphere-2022-336
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2022-336
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
03 Jun 2022
| 03 Jun 2022
Daytime along-valley winds in the Himalayas as simulated by the WRF–model
Abstract. Local valley winds in four major valleys on the southern slope of the Nepal Himalayas are studied by means of high resolution meteorological modelling. The Weather Research and Forecasting model is run with a 1 km horizontal grid spacing covering a 5 day period in December 2014. Model evaluation against meteorological observations from three automatic weather stations in Khumbu valley (one of the four valleys) shows a good agreement between the modelled and observed daily cycle of the near-surface wind speed and direction. Well defined daytime up-valley winds are found in all of the four valleys. The night-time along-valley winds are weak in magnitude and flow mostly in the up-valley direction. The diurnal cycle of the winds is interrupted more during the days with large-scale northerly winds than during the westerlies which is most likely due to channelling of the above-valley winds into the valley atmosphere. Differences in the daytime up-valley winds are found between the valleys and their parts. Since the valleys are under similar large-scale forcing, the differences are assumed to be due to differences in the valley topographies. Parts of the valleys with steep valley floor inclination (2–5 degrees) are associated with weaker and shallower daytime up-valley winds compared to the parts which have nearly flat valley floors (<1 degrees). In the four valleys, the ridge heights also increase along the valley, meaning that the valley floor inclination does not necessarily lead to a reduction in the volume of the valley atmosphere. This way the dominant driving mechanism of the along-valley winds could shift from the valley volume effect to buoyant forcing due to the inclination. Two of the valleys have a 1 km high barrier in their entrances between the valley and the plain. Winds at the valley entrances of these two valleys are weaker when comparing to the open valley entrances. Strong and shallow winds, resembling down-slope winds, are found on the lee-side slope of the barrier followed by weaker and deeper winds at the valley entrance, 20 km towards the valley from the barrier.
How to cite. Mikkola, J., Sinclair, V., Bister, M., and Bianchi, F.: Daytime along-valley winds in the Himalayas as simulated by the WRF–model, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2022-336, 2022.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
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18 Jan 2023
Daytime along-valley winds in the Himalayas as simulated by the Weather Research and Forecasting (WRF) model
Johannes Mikkola, Victoria A. Sinclair, Marja Bister, and Federico Bianchi
Atmos. Chem. Phys., 23, 821–842, https://doi.org/10.5194/acp-23-821-2023, https://doi.org/10.5194/acp-23-821-2023, 2023
Short summary
Short summary
Local winds in four valleys located in the Nepal Himalayas are studied by means of high-resolution meteorological modelling. Well-defined daytime up-valley winds are simulated in all of the valleys with some variation in the flow depth and strength among the valleys and their parts. Parts of the valleys with a steep valley floor inclination (2–5°) are associated with weaker and shallower daytime up-valley winds compared with the parts that have nearly flat valley floors (< 1°).
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2022-336', Emily Potter, 23 Jun 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-336/egusphere-2022-336-RC1-supplement.pdf
-
RC2: 'Comment on egusphere-2022-336', Anonymous Referee #2, 26 Jun 2022
The manuscript titled “Daytime along-valley winds in the Himalayas as simulated by the WRF–model” is a good attempt to simulate winds particularly along the valleys in the complex terrain of Himalayan Mountains. In this work, four neighboring valleys are identified for the investigation on along-valley and cross-valley circulations in the Nepal Himalaya using the WRF model. Interestingly, point highlighted here is the interaction between local induced circulation and synoptic-scale flow, however, there are major concerns associated with methodology and persisting in the interpretation of the results as well.
Major comments
- The five days period is too small for investigating the influence of synoptic scale flows on valley circulations, hence required to be explored to a longer time scale as strong seasonality may be associated with synoptic flows. The synoptic-scale flow are found to show pronounced variations from northerlies to the westerly. This could be due to the trough region embedded in the upper-level westerlies and moving eastward. If the longer period is considered, the overall variation of the synoptic-scale flow may change, and at some point, it can be southerly or southwesterly, which can strongly support the along-valley flows. Diurnality will also have a profound influence on the topographic flows due to thermal gradients.
- It is suggested to select a longer time period of at least two contrasting seasons. The valley inversions dominate during winter, and that might be confined within the valley region. The selected period is of winter, where the solar insulation is comparatively low, and the inversion can persist for a longer time. This can also affect along-valley flow.
- There are some issues with the model configurations and simulation. The spin-up time is not seen to be considered. The Land-surface scheme is not specified here, while it strongly impacts the near-surface fluxes and meteorological fields.
- One of the major challenges to the models is to simulate the weak flow conditions. The local induced circulation is more prominent during the weak synoptic-scale flow (Solanki et al. 2019, BLM). It is strongly suggested here to investigate the model performance for two different wind flow regimes; low and strong. That can be performed only if the longer time period for simulations is taken into account.
- A robust discussion was missing on how the selection of five days is made.
- The wind follows the logarithmic variation within the surface layer. So it is suggested to compare the simulated winds to the observations at similar elevations (5m).
- The brief description on the observational data is not added here. In order to have close agreement, the comparison of the model output, preferably, is required to be made with the closest available instantaneous observations, along with mean values.
- Why is the altitude adjustment discarded? The actual altitude and model altitude comparison could be added to the description.
- Discuss the model evaluations using other matrices such as correlations, RMSE, and Mean Bias Error. In the comparison table, the MAE is much higher than the addressed benchmark values in literature, e.g., Emery et al., (2001). In addition, it would be interesting if the diurnal variation of wind and other meteorological variables, is presented. The WRF shows limited performance in simulating the diurnal cycle of winds over the Himalayas region (Singh et al., 2021).
- Line 176, the decomposition of the vector A, into along- and cross-valley is carried out taking the three-points on either sides of valley center, to avoid the sharp gradients. However, the valley is narrowing towards the north, so the taking six points for the actual orientation of the valley, will change largely, and hence may not be a close representation. Here it is suggested to compare these two components, along-valley, and cross-valley, by choosing one-, two- and three points. If there is not large variability between one- and three-, the orientation of the valley may be considered to be represented correctly.
- The investigation of the cross-valley component is not discussed in detail. The cross-section of the valleys for 19-21 December showing the intrusion of the synoptic-scale flow into the valley region is to be presented/plotted.
Specific comment:
- In figure 2, there are some visible artifacts (locations of about 1000m high, as per the scale) on the topography data, along the costal lines extending from Arabian Sea to Bay of Bengal. Topography needs to be checked.
- Line 126-128: The local circulations change with the day-night contrast including two transitions during sunset and sunrise. Better to select the stable atmosphere during nighttime and convective daytime hours by discarding such transitions.
- Line 144-145: The observed wind speed is below 2 ms -1, while the corresponding MAE is 2.1 ms-1. The model performance is not very convincing for the low wind conditions.
- Line 163-164: it would be interesting to see a close view of the individual valley, (possibly 3-d view to have a better understanding of the orientation and shapes) that will highlight the geometrical differences between the valleys.
- Line 166: How is this criterion selected?
- Line 226: Is it the pressure level corresponding to the ridge height? What is the criterion of this selection? Why not 500hPa, which is generally used in synoptic weather charts?
- Line 226-228: this discussion may change for the longer run of the model.
- Line 242: This is not a sufficient explanation for neglecting this period here. The interaction between two flows should be investigated separately.
- Line 243: During 19-21 Dec, the flow is reported to be westerlies, while it can still impact the thermal winds in the valleys like northerly, depending upon the orientation of the valleys and magnitude of the westerlies. How can the interruption of the thermal winds by synoptic westerlies be neglected?
- Figure 2: Why the valley width is missing at some grid points?
- Line 246: Is it thermal-induced local circulation or synoptic flow? Moreover, it is unlikely characteristic of mountain meteorology, if it is happening so (evening time upslope winds), then meteorological processes operating at high altitudes are required to be investigated with specific observational experiments.
- Figure 4: Remove the extra contour lines related to the topography. Due to the jumbling contour lines, the wind field is not very clear.
- Line 265-266: How the diurnal cycle is explained by taking a single hour. If the northerlies prevailed during 17-18 Dec, it would remain unchanged irrespective of the hour.
- Line 275-276: Show the observation and model comparison for these calm wind conditions. It is very interesting if the model and observations are in agreement.
- Figure 5: The scale on y-axis is not correct. Many of the points are out of the scale and not visible.
- Line 333: But not all valleys are north-south oriented. These model levels can be well above the near valley inversions during the nighttime.
- Line 366-367: Suggested to add a figure on valley cross-section wind.
Citation: https://doi.org/10.5194/egusphere-2022-336-RC2 -
AC1: 'Comment on egusphere-2022-336', Johannes Mikkola, 31 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-336/egusphere-2022-336-AC1-supplement.pdf
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2022-336', Emily Potter, 23 Jun 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-336/egusphere-2022-336-RC1-supplement.pdf
-
RC2: 'Comment on egusphere-2022-336', Anonymous Referee #2, 26 Jun 2022
The manuscript titled “Daytime along-valley winds in the Himalayas as simulated by the WRF–model” is a good attempt to simulate winds particularly along the valleys in the complex terrain of Himalayan Mountains. In this work, four neighboring valleys are identified for the investigation on along-valley and cross-valley circulations in the Nepal Himalaya using the WRF model. Interestingly, point highlighted here is the interaction between local induced circulation and synoptic-scale flow, however, there are major concerns associated with methodology and persisting in the interpretation of the results as well.
Major comments
- The five days period is too small for investigating the influence of synoptic scale flows on valley circulations, hence required to be explored to a longer time scale as strong seasonality may be associated with synoptic flows. The synoptic-scale flow are found to show pronounced variations from northerlies to the westerly. This could be due to the trough region embedded in the upper-level westerlies and moving eastward. If the longer period is considered, the overall variation of the synoptic-scale flow may change, and at some point, it can be southerly or southwesterly, which can strongly support the along-valley flows. Diurnality will also have a profound influence on the topographic flows due to thermal gradients.
- It is suggested to select a longer time period of at least two contrasting seasons. The valley inversions dominate during winter, and that might be confined within the valley region. The selected period is of winter, where the solar insulation is comparatively low, and the inversion can persist for a longer time. This can also affect along-valley flow.
- There are some issues with the model configurations and simulation. The spin-up time is not seen to be considered. The Land-surface scheme is not specified here, while it strongly impacts the near-surface fluxes and meteorological fields.
- One of the major challenges to the models is to simulate the weak flow conditions. The local induced circulation is more prominent during the weak synoptic-scale flow (Solanki et al. 2019, BLM). It is strongly suggested here to investigate the model performance for two different wind flow regimes; low and strong. That can be performed only if the longer time period for simulations is taken into account.
- A robust discussion was missing on how the selection of five days is made.
- The wind follows the logarithmic variation within the surface layer. So it is suggested to compare the simulated winds to the observations at similar elevations (5m).
- The brief description on the observational data is not added here. In order to have close agreement, the comparison of the model output, preferably, is required to be made with the closest available instantaneous observations, along with mean values.
- Why is the altitude adjustment discarded? The actual altitude and model altitude comparison could be added to the description.
- Discuss the model evaluations using other matrices such as correlations, RMSE, and Mean Bias Error. In the comparison table, the MAE is much higher than the addressed benchmark values in literature, e.g., Emery et al., (2001). In addition, it would be interesting if the diurnal variation of wind and other meteorological variables, is presented. The WRF shows limited performance in simulating the diurnal cycle of winds over the Himalayas region (Singh et al., 2021).
- Line 176, the decomposition of the vector A, into along- and cross-valley is carried out taking the three-points on either sides of valley center, to avoid the sharp gradients. However, the valley is narrowing towards the north, so the taking six points for the actual orientation of the valley, will change largely, and hence may not be a close representation. Here it is suggested to compare these two components, along-valley, and cross-valley, by choosing one-, two- and three points. If there is not large variability between one- and three-, the orientation of the valley may be considered to be represented correctly.
- The investigation of the cross-valley component is not discussed in detail. The cross-section of the valleys for 19-21 December showing the intrusion of the synoptic-scale flow into the valley region is to be presented/plotted.
Specific comment:
- In figure 2, there are some visible artifacts (locations of about 1000m high, as per the scale) on the topography data, along the costal lines extending from Arabian Sea to Bay of Bengal. Topography needs to be checked.
- Line 126-128: The local circulations change with the day-night contrast including two transitions during sunset and sunrise. Better to select the stable atmosphere during nighttime and convective daytime hours by discarding such transitions.
- Line 144-145: The observed wind speed is below 2 ms -1, while the corresponding MAE is 2.1 ms-1. The model performance is not very convincing for the low wind conditions.
- Line 163-164: it would be interesting to see a close view of the individual valley, (possibly 3-d view to have a better understanding of the orientation and shapes) that will highlight the geometrical differences between the valleys.
- Line 166: How is this criterion selected?
- Line 226: Is it the pressure level corresponding to the ridge height? What is the criterion of this selection? Why not 500hPa, which is generally used in synoptic weather charts?
- Line 226-228: this discussion may change for the longer run of the model.
- Line 242: This is not a sufficient explanation for neglecting this period here. The interaction between two flows should be investigated separately.
- Line 243: During 19-21 Dec, the flow is reported to be westerlies, while it can still impact the thermal winds in the valleys like northerly, depending upon the orientation of the valleys and magnitude of the westerlies. How can the interruption of the thermal winds by synoptic westerlies be neglected?
- Figure 2: Why the valley width is missing at some grid points?
- Line 246: Is it thermal-induced local circulation or synoptic flow? Moreover, it is unlikely characteristic of mountain meteorology, if it is happening so (evening time upslope winds), then meteorological processes operating at high altitudes are required to be investigated with specific observational experiments.
- Figure 4: Remove the extra contour lines related to the topography. Due to the jumbling contour lines, the wind field is not very clear.
- Line 265-266: How the diurnal cycle is explained by taking a single hour. If the northerlies prevailed during 17-18 Dec, it would remain unchanged irrespective of the hour.
- Line 275-276: Show the observation and model comparison for these calm wind conditions. It is very interesting if the model and observations are in agreement.
- Figure 5: The scale on y-axis is not correct. Many of the points are out of the scale and not visible.
- Line 333: But not all valleys are north-south oriented. These model levels can be well above the near valley inversions during the nighttime.
- Line 366-367: Suggested to add a figure on valley cross-section wind.
Citation: https://doi.org/10.5194/egusphere-2022-336-RC2 -
AC1: 'Comment on egusphere-2022-336', Johannes Mikkola, 31 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-336/egusphere-2022-336-AC1-supplement.pdf
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Johannes Mikkola on behalf of the Authors (31 Aug 2022)
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Manuscript
ED: Referee Nomination & Report Request started (05 Sep 2022) by Peter Haynes
RR by Emily Potter (17 Sep 2022)
RR by Anonymous Referee #2 (13 Oct 2022)
ED: Publish subject to minor revisions (review by editor) (17 Oct 2022) by Peter Haynes
AR by Johannes Mikkola on behalf of the Authors (04 Nov 2022)
Author's response
Author's tracked changes
Manuscript
ED: Publish subject to minor revisions (review by editor) (25 Nov 2022) by Peter Haynes
AR by Johannes Mikkola on behalf of the Authors (29 Nov 2022)
Author's response
Author's tracked changes
Manuscript
ED: Publish as is (14 Dec 2022) by Peter Haynes
AR by Johannes Mikkola on behalf of the Authors (19 Dec 2022)
Manuscript
Journal article(s) based on this preprint
18 Jan 2023
Daytime along-valley winds in the Himalayas as simulated by the Weather Research and Forecasting (WRF) model
Johannes Mikkola, Victoria A. Sinclair, Marja Bister, and Federico Bianchi
Atmos. Chem. Phys., 23, 821–842, https://doi.org/10.5194/acp-23-821-2023, https://doi.org/10.5194/acp-23-821-2023, 2023
Short summary
Short summary
Local winds in four valleys located in the Nepal Himalayas are studied by means of high-resolution meteorological modelling. Well-defined daytime up-valley winds are simulated in all of the valleys with some variation in the flow depth and strength among the valleys and their parts. Parts of the valleys with a steep valley floor inclination (2–5°) are associated with weaker and shallower daytime up-valley winds compared with the parts that have nearly flat valley floors (< 1°).
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Johannes Mikkola
CORRESPONDING AUTHOR
Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, Finland
Victoria Sinclair
Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, Finland
Marja Bister
Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, Finland
Federico Bianchi
Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, Finland
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Short summary
Local winds in four valleys located in the Nepal Himalayas are studied by means of high-resolution meteorological modelling. Well defined daytime up-valley winds are simulated in all of the valleys with some variation in the flow depth and strength between the valleys and their parts. Parts of the valleys with steep valley floor inclination (2–5 degrees) are associated with weaker and shallower daytime up-valley winds compared to the parts which have nearly flat valley floors (<1 degrees).
Local winds in four valleys located in the Nepal Himalayas are studied by means of...