# Spatio-Temporal Analysis of Valley Wind Systems in the Complex Mountain Topography of the Rolwaling Himal, Nepal

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area

#### 2.2. Station Network

#### 2.3. Data Processing

#### 2.4. Data Analysis and Visualization Methods

## 3. Results

#### 3.1. Mean Valley Wind Day Wind Speeds and Seasonal Pattern at Na and NE Bottom Station

#### 3.1.1. Na Station

#### 3.1.2. NE Bottom Station

#### 3.2. Spatio-Temporal Forming of Mountain–Valley Wind-System on a Valley Wind Day

## 4. Discussion

#### 4.1. Data Coverage

#### 4.2. Diurnal and Seasonal Patterns of the Stations

#### 4.3. Error Discussion, Limitations, and Further Research

## 5. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

AWS | automatic weather station |

DEM | digital elevation model |

ISM | Indian summer monsoon |

MVWS | mountain–valley wind system |

PISR | potential incoming solar radiation |

SD | standard deviation |

VWD | valley wind day |

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**Figure 2.**Overview of days identified as valley wind days (VWDs) during the observational period. Black columns indicate VWDs. Months are indicated above the columns.

**Figure 3.**Wind speeds and direction during valley wind days at Na station. Topmost position (

**a**) shows the hourly mean value of wind speed on the VWD as bar height with the red SD whisker. Hourly data are provided as black dots. Plot (

**b**) consists of the hourly means of temperature (blue) and mean incoming solar radiation sums (yellow) on VWDs. Whiskers of one SD are added to the parameters in the respective colors. Mean hourly wind speeds for every hour in the observational period are shown in (

**c**). The bottom plot (

**d**) shows hourly wind directions in the same period. Calm hours are shown as transparent boxes in (

**d**). Both (

**c**) and (

**d**) show the VWD data with higher lumination.

**Figure 5.**Wind speeds and direction during valley wind days at NE bottom station. Topmost position (

**a**) shows the hourly mean value of wind speed on the VWD as bar height with the red SD whisker. Hourly data are provided as black dots. Plot (

**b**) consists of the hourly means of temperature (blue) and mean incoming solar radiation sums (yellow) on the VWD. Whiskers of one SD are added to the parameters in the respective colors. Mean hourly wind speeds for every hour in the observational period are shown in (

**c**). The bottom plot (

**d**) shows hourly wind directions in the same period. Calm hours are shown as transparent boxes in (

**d**). Both (

**c**) and (

**d**) show the VWD data with higher lumination.

**Figure 7.**Diurnal forming of the winds in the Rolwaling Valley on 22 November 2017. Sub-figures showing the mean hourly wind speeds of the first hour of the day (00:00 – 01:00) in the top-left. The hour between 04:00 and 05:00 at the top-right, and the hours following 06:00 and 08:00 in the bottom row left and right respectively. Arrows indicate the wind direction at the stations, with the wind speed shown by the size of the arrow. Calm hours and hours with less than 0.3 m s${}^{-1}$ are indicated by circles.

**Figure 8.**Diurnal forming of the winds in the Rolwaling Valley on 22 November 2017. Sub-figures showing the mean hourly wind speeds of the first hour of the day (12:00 – 13:00) in the top-left. The hour between 15:00 and 16:00 at the top-right, and the hours following 18:00 and 21:00 in the bottom row left and right respectively. Arrows indicate the wind direction at the stations, with the wind speed shown by the size of the arrow. Calm hours and hours with less than 0.3 m s${}^{-1}$ are indicated by circles.

**Figure 9.**Potential incoming solar radiation over the study area on 22 November 2017. Calculated using ALOS (AW3D) by JAXA and SAGA-GIS [65].

**Table 1.**Automated weather station (AWS) in the TREELINE station network [9]. Mean hourly wind speeds were calculated within the period of 1 October 2017 to 30 September 2018.

Station | Latitude (${}^{\circ}$N) | Longitude (${}^{\circ}$E) | Elevation (m a.s.l.) | Position | Mean Hourly Wind Speed (m s${}^{-1}$) |
---|---|---|---|---|---|

NW bottom | 27.9009 | 86.3762 | 3718.9 | Valley floor | 0.62 |

NE bottom | 27.8986 | 86.3791 | 3734.2 | Valley floor | 1.08 |

Na | 27.8782 | 86.4337 | 4192.1 | Valley floor | 1.66 |

Dudgunda | 27.8756 | 86.4604 | 4532.2 | Valley floor | 1.25 |

Gompa | 27.9050 | 86.3755 | 3886.0 | Slope | 0.94 |

NW top | 27.8967 | 86.3742 | 4035.9 | Slope | 1.46 |

NE top | 27.8934 | 86.3759 | 4158.3 | Slope | 1.14 |

Yalun | 27.8590 | 86.4338 | 5005.2 | Slope | — |

**Table 2.**Sensor properties according to the manufacturer Onset Computer Corporation, Bourne, MA 02532, USA [61].

Sensor Type | Sensor ID | Measurement Range | Operating Range | Other Details |
---|---|---|---|---|

Weather station data logger | U30-NRC | −40–60 ${}^{\circ}$C | Logging interval: 15 min (user defined), storage capacity: 512 Kb flash storage | |

Wind speed | S-WSB-M003 | 0–76 m s${}^{-1}$, accuracy: ±1.1 m s${}^{-1}$ or ±4%, automatic averaging | −40–75 ${}^{\circ}$C | Starting threshold: 1 m s${}^{-1}$ horizontal movement |

Wind direction | S-WDA-M003 | 0–355${}^{\circ}$, 5${}^{\circ}$ dead band, accuracy: ±5${}^{\circ}$, unit vector averaging | −40–70 ${}^{\circ}$C | Starting threshold: 1 m s${}^{-1}$ resolution: 1.4${}^{\circ}$ horizontal movement |

Solar radiation | S-LIB-M003 | −1280 W m${}^{-2}$, Accuracy: ±10 W m${}^{-2}$, Drift: <±2% per year | −40–75 ${}^{\circ}$C | ±0.38 W m${}^{-2}$ error at conditions >25 ${}^{\circ}$C, Spectral range: 300–1100 nm |

Temperature | S-THB-M008 | −40–75 ${}^{\circ}$C, accuracy: ±0.02 from 0–50 ${}^{\circ}$C, drift: <0.1 ${}^{\circ}$C per year | −40–75 ${}^{\circ}$C | |

Rain gauge | S-RGB-M002 | 0–12.7 cm h${}^{-1}$, Max. 4000 tips per logging interval, accuracy: ±1.0 at 20 mm h${}^{-1}$ | 0–50 ${}^{\circ}$C | Resolution: 0.2 mm |

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## Share and Cite

**MDPI and ACS Style**

Jentsch, H.; Weidinger, J. Spatio-Temporal Analysis of Valley Wind Systems in the Complex Mountain Topography of the Rolwaling Himal, Nepal. *Atmosphere* **2022**, *13*, 1138.
https://doi.org/10.3390/atmos13071138

**AMA Style**

Jentsch H, Weidinger J. Spatio-Temporal Analysis of Valley Wind Systems in the Complex Mountain Topography of the Rolwaling Himal, Nepal. *Atmosphere*. 2022; 13(7):1138.
https://doi.org/10.3390/atmos13071138

**Chicago/Turabian Style**

Jentsch, Helge, and Johannes Weidinger. 2022. "Spatio-Temporal Analysis of Valley Wind Systems in the Complex Mountain Topography of the Rolwaling Himal, Nepal" *Atmosphere* 13, no. 7: 1138.
https://doi.org/10.3390/atmos13071138