scholarly journals Relationship between topography, tropospheric wind, and frequency of mountain waves in the upper mesosphere over the Kanto area of Japan

2022 ◽  
Vol 74 (1) ◽  
Author(s):  
Satoshi Ishii ◽  
Yoshihiro Tomikawa ◽  
Masahiro Okuda ◽  
Hidehiko Suzuki
Keyword(s):  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Observation Site ◽  
Mountain Waves ◽  
Westerly Winds ◽  
Geostationary Meteorological Satellite ◽  
Good Proxy ◽  
Low Incidence ◽  
Wind Profiles ◽  
Meteorological Satellite

AbstractImaging observations of OH airglow were performed at Meiji University, Japan (35.6° N, 139.5° E), from May 2018 to December 2019. Mountainous areas are located to the west of the imager, and westerly winds are dominant in the lower atmosphere throughout the year. Mountain waves (MWs) are generated and occasionally propagate to the upper atmosphere. However, only four likely MW events were identified, which are considerably fewer than expected. There are two possible reasons for the low incidence: (1) MWs do not propagate easily to the upper mesosphere due to background wind conditions, and/or (2) the frequency of MW excitation was low around the observation site. Former possibility is found not to be a main reason to explain the frequency by assuming typical wind profiles in troposphere and upper mesosphere over Japan. Thus, frequency and spatial distribution of orographic wavy clouds were investigated by analyzing images taken by the Himawari-8 geostationary meteorological satellite in 2018. The number of days when wavy clouds were detected in the troposphere around the observation site (Kanto area) was about a quarter of that around the Tohoku area. This result indicates that frequency of over-mountain flow which is thought to be a source of excitation of MWs is low in Kanto area. We also found that the angle between the horizontal wind direction in troposphere and the orientation of the mountain ridge is a good proxy for the occurrence of orographic wavy clouds, i.e., excitation of MWs. We applied this proxy to the topography around the world to investigate regions where MWs are likely to be excited frequently throughout the year to discuss the likelihood of "MW hotspots" at various spatial scale. Graphical Abstract

Frequency of Mountain Waves Over Kanto Area Revealed by Imaging Observations of OH Airglow

2021 ◽  
Author(s):  
Satoshi Ishii ◽  
Yoshihiro Tomikawa ◽  
Masahiro Okuda ◽  
Hidehiko Suzuki
Keyword(s):  
Spatial Scales ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Leeward Side ◽  
Mountainous Areas ◽  
Wind Fields ◽  
Mountain Waves ◽  
The World ◽  
Geostationary Meteorological Satellite ◽  
Good Proxy

Abstract Imaging observations of OH airglow were conducted at Meiji University, Japan (IN, mE), from May 2018 to December 2019. Mountainous areas, including Mt. Fuji, are located to the west of the imager, and westerly winds are dominant in the lower atmosphere throughout the year. Mountain waves (MWs) are generated on the leeward sides of mountains and occasionally propagate to the upper atmosphere. However, during the observation period (about 1 year and 8 months), only four possible MW events were identified. Based on previous reports, this incidence is considerably lower than expected. There are two possible reasons for the low incidence of MW events: (1) The frequency of MW excitation is small in the lower layers of the atmosphere, and/or (2) MWs do not propagate easily to the upper mesosphere due to background wind conditions. This study verified the likelihood of the former case. Under over-mountain airflow conditions, wavy clouds are often generated on the leeward side. Since over-mountain airflow is essential for the excitation of MWs, the frequency of wavy clouds in the lower atmosphere can be regarded as a measure of the occurrence of MWs. The frequency and spatial distribution of MWs around Japan were investigated by detecting the wavy clouds from color images taken by the Himawari-8 geostationary meteorological satellite (GSM-8) for one year in 2018. The wavy clouds were detected on more than 70 days a year around the Tohoku region, but just 20 days a year around Mt. Fuji. This suggests that few MWs are generated around Mt. Fuji. The differences between these two regions were examined focusing on the relationship between the local topography and dominant horizontal wind fields in the lower atmosphere. Specifically, the findings showed that the angle between the dominant horizontal wind direction and the orientation of the mountain ridge is a good proxy of the occurrence of wavy clouds, i.e., excitation of MWs in mountainous areas. We have also applied this proxy to topography in other areas of the world to investigate areas where MWs would be occurring frequently. Finally, we discuss the likelihood of "MW hotspots" at various spatial scales in the world.

scholarly journals Case Study and Climatological Analysis of Upper-Tropospheric Jet Stream and Stratosphere–Troposphere Exchanges Using VHF Profilers and Radionuclide Measurements in France

2017 ◽  
Vol 56 (11) ◽  
pp. 3081-3097 ◽  
Author(s):  
Jean-Luc Baray ◽  
Yves Pointin ◽  
Joël Van Baelen ◽  
Marie Lothon ◽  
Bernard Campistron ◽  
...  
Keyword(s):  
Activity Ratio ◽  
Horizontal Wind ◽  
Jet Stream ◽  
Cosmogenic Radionuclides ◽  
Stratospheric Intrusion ◽  
Westerly Winds ◽  
Seasonal Wind ◽  
The Mean ◽  
Wind Profiles

AbstractThe authors present a climatological analysis of tropospheric horizontal wind profiles and jet stream events using long series of wind profiles from two VHF profilers located in France: Lannemezan (2001–14) and Opme (1999–2014). A case study of jet stream and stratospheric intrusion of air into the troposphere that occurred in January 2013 is first described and demonstrates the capability of the VHF profilers to detect jet stream events. The climatology study over the two sites reveals the strongest values of seasonal wind during winter (21.4 m s−1 at 8.7-km height at Opme; 25.1 m s−1 at 9.6-km height at Lannemezan). A methodology based on the automatic detection of maximum winds on a decadal series of hourly wind profiles allows the detection of jet stream events and establishes its climatology for each site. A frequency analysis of jet stream events of westerly winds over 50 m s−1 presents a clear seasonality at the two sites, with a maximum in winter (3.5%–9.7% of hourly profiles) and a minimum in summer (near 1%). Cosmogenic radionuclides sampled at Opme also exhibit a clear seasonal variation with maximum in spring and minimum in the cold seasons; the 7Be/22Na activity ratio confirms stratosphere-to-troposphere exchanges for the studied cases. The mean interannual variability of the frequency of jet stream events is 1.5% in Opme and 2.9% in Lannemezan. Positive decadal trends are observed for the two sites: +1.6 ± 1.2% decade−1 for Opme and +2.4 ± 2.2% decade−1 for Lannemezan.

scholarly journals Evaluation of wind profiles from the NERC MST radar, Aberystwyth, UK

2014 ◽  
Vol 7 (9) ◽  
pp. 3113-3126 ◽  
Author(s):  
C. F. Lee ◽  
G. Vaughan ◽  
D. A. Hooper
Keyword(s):  
Wind Speed ◽  
Sampling Error ◽  
Signal To Noise Ratio ◽  
Weather Prediction ◽  
Horizontal Wind ◽  
Mountain Waves ◽  
Wind Speeds ◽  
Mst Radar ◽  
Wind Profiles ◽  
Aspect Sensitivity

Abstract. This study quantifies the uncertainties in winds measured by the Aberystwyth Mesosphere–Stratosphere–Troposphere (MST) radar (52.4° N, 4.0° W), before and after its renovation in March 2011. A total of 127 radiosondes provide an independent measure of winds. Differences between radiosonde and radar-measured horizontal winds are correlated with long-term averages of vertical velocities, suggesting an influence from local mountain waves. These local influences are an important consideration when using radar winds as a measure of regional conditions, particularly for numerical weather prediction. For those applications, local effects represent a source of sampling error additional to the inherent uncertainties in the measurements themselves. The radar renovation improved the signal-to-noise ratio (SNR) of measurements, with a corresponding improvement in altitude coverage. It also corrected an underestimate of horizontal wind speeds attributed to beam formation problems, due to pre-renovation component failure. The root mean square error (RMSE) in radar-measured horizontal wind components, averaged over half an hour, increases with wind speed and altitude, and is 0.8–2.5 m s−1 (6–12% of wind speed) for post-renovation winds. Pre-renovation values are typically 0.1 m s−1 larger. The RMSE in radial velocities is <0.04 m s−1. Eight weeks of special radar operation are used to investigate the effects of echo power aspect sensitivity. Corrections for echo power aspect sensitivity remove an underestimate of horizontal wind speeds; however aspect sensitivity is azimuthally anisotropic at the scale of routine observations (≈1 h). This anisotropy introduces random error into wind profiles. For winds averaged over half an hour, the RMSE is around 3.5% above 8 km, but as large as 4.5% in the mid-troposphere.

scholarly journals Frequency variations of gravity waves interacting with a time-varying tide

2013 ◽  
Vol 31 (10) ◽  
pp. 1731-1743 ◽  
Author(s):  
C. M. Huang ◽  
S. D. Zhang ◽  
F. Yi ◽  
K. M. Huang ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Frequency Variation ◽  
Time Varying ◽  
Transient Nature ◽  
Critical Layers ◽  
Favorable Conditions ◽  
Frequency Variations

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

scholarly journals Wind profile correction algorithm based on Atmospheric Boundary Layer stability profile

2021 ◽  
Author(s):  
Francisco Albuquerque Neto ◽  
Vinicius Almeida ◽  
Julia Carelli
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Profile ◽  
Horizontal Wind ◽  
Boundary Layer Stability ◽  
Correction Algorithm ◽  
Horizontal Wind Speed ◽  
Study Region ◽  
Profile Correction ◽  
Wind Profiles

&lt;p&gt;In recent years, the use of radar wind profilers (RWP) at airports has grown significantly with the aim of supporting decision makers to maintain the safety of aircraft landings and takeoffs.&lt;/p&gt;&lt;p&gt;The RWP provide vertical profiles of averaged horizontal wind speed and direction and vertical wind velocity for the entire Atmospheric Boundary Layer (ABL) and beyond. In addition, RWP with Radio-Acoustic Sounding System (RASS) are able to retrieve virtual temperature profiles in the ABL.&lt;/p&gt;&lt;p&gt;RWP data evaluation is usually based on the so-called Doppler Beam Swinging method (DBS) which assumes homogeneity and stationarity of the wind field. Often, transient eddies violate this homogeneity and stationarity requirement. Hence, incorrect wind profiles can relate to transient eddies and present a problem for the forecast of high-impact weather phenomena in airports. This work intends to provide a method for removing outliers in such profiles based on historical data and other variables related to the Atmospheric Boundary Layer stability profile in the study region.&lt;/p&gt;&lt;p&gt;For this study, a dataset of almost one year retrieved from a RWP LAP3000 with RASS Extension is used for a wind profile correction algorithm development.&lt;/p&gt;&lt;p&gt;The algorithm consists of the detection of outliers in the wind profiles based on the thermodynamic structure of the ABL and the generation of the corrected profiles.&lt;/p&gt;&lt;p&gt;Results show that the algorithm is capable of identifying and correcting unrealistic variations in speed caused by transient eddies. The method can be applied as a complement to the RWP data processing for better data reliability.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Keywords: atmospheric boundary layer; stability profile; wind profile&lt;/p&gt;

scholarly journals Analyzing the basic meteorological aspects of a particulate air pollution episode over the industrial area of Northwestern Greece during the November of 2009

2013 ◽  
Vol 15 (2) ◽  
pp. 241-253 ◽  
Keyword(s):  
Air Pollution ◽  
Particulate Matter ◽  
Wind Field ◽  
Lower Troposphere ◽  
Airborne Particulate Matter ◽  
Radical Change ◽  
Industrial Area ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Pollution Episode

The complex terrain basin of Amyntaio – Ptolemais – Kozani in Western Macedonia of Greece is an area characterized by increased industrial activity and therefore it demands continuous and assiduous environmental monitoring. A prolonged particulate matter air pollution episode was recorded in the area during November 2009. Basic meteorological aspects are analyzed, during the episode period. Daily and hourly PM10 and PM2.5 concentration measurements were used along with surface and lower atmosphere hourly meteorological parameters from 13 measuring stations. The observational data were supported by data produced by the meteorological component of an air pollution model. The overall analysis showed that the episode was primarily the result of the synoptic setting of the middle and lower troposphere. An Omega blocking pattern which gradually transformed to a high-over-low pattern prevailed over central and southern Europe during the episode’s period. The examination of the vertical wind field in the lower troposphere and appropriate stability indices, revealed a continuous absence of significant convection. The weak horizontal wind field near the surface and the reduced mixing height combined with the lack of synoptic forcing resulted in the trapping of the pollutants in the lower troposphere and the recording of increased airborne particulate matter concentrations. The radical change of the synoptic setting in the first days of December marked the end of the episode.

scholarly journals Estimating Sunshine Duration Using Hourly Total Cloud Amount Data from a Geostationary Meteorological Satellite

Atmosphere ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 26
Author(s):  
Weiwei Zhu ◽  
Bingfang Wu ◽  
Nana Yan ◽  
Zonghan Ma ◽  
Linjiang Wang ◽  
...  
Keyword(s):  
Sunshine Duration ◽  
Regional Scale ◽  
Cloud Amount ◽  
Important Indicator ◽  
Study Region ◽  
Total Cloud Amount ◽  
Cloud Coverage ◽  
Ground Observation ◽  
Geostationary Meteorological Satellite ◽  
Meteorological Satellite

Sunshine duration is an important indicator of the amount of solar radiation received in a region and an important input parameter for the study of atmospheric energy balance, climate change, ecosystem evolution, and social sustainability. Currently, extrapolation and interpolation of data from meteorological stations are the most common methods used to calculate sunshine duration on a regional scale. However, it is difficult to obtain high precision sunshine duration in areas lacking ground observation or where sunshine duration is highly heterogeneous on the ground. In this paper, a new method is proposed to estimate sunshine duration with hourly total cloud amount (CTA) data from sunrise to sunset derived from the Fengyun-2G geostationary meteorological satellite (FY-2G). This method constructs a new index known as daytime mean total cloud coverage amount and provides quadratic equations relating daytime mean total cloud coverage amount to relative sunshine duration in different seasons. The method was validated with ground observation data for 2016 from 18 meteorological stations in the Three-River Headwaters Region of Qinghai Province, China. For individual stations, the coefficient of determination (R2) between estimated and measured sunshine was at least 0.894, the RMSE (root mean square error) was 0.977 h/day or less, the MAE (mean absolute error) was 0.824 h/day or less, the RE (relative error) was 0.150 or lower, and the value of d was 0.963 or greater, which validated that the proposed method can effectively predict daily sunshine duration. These equations can also provide higher precision estimates of regional-scale sunshine duration. This was demonstrated by comparing, for the entire study region, the spatial distribution of sunshine duration estimated from season-based equations with results from three different interpolation methods based on ground observations. Overall, the study confirms that total cloud amount measures from a geostationary satellite can be used to successfully estimate sunshine duration.

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