meridional wind
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2022 ◽  
Author(s):  
Alessandro Carlo Maria Savazzi ◽  
Louise Nuijens ◽  
Irina Sandu ◽  
Geet George ◽  
Peter Bechtold

Abstract. The characterization of systematic forecast errors in lower-tropospheric winds over the ocean is a primary need for reforming models. Winds are among the drivers of convection, thus an accurate representation of winds is essential for better convective parameterizations. We focus on the temporal variability and vertical distribution of lower-tropospheric wind biases in operational medium-range weather forecasts and ERA5 reanalyses produced with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Thanks to several sensitivity experiments and an unprecedented wealth of measurements from the 2020 EUREC4A field campaign, we show that the wind bias varies greatly from day to day, resulting in RSME's up to 2.5 m s−1, with a mean wind speed bias up to −1 m s−1 near and above the trade-inversion in the forecasts and up to −0.5 m s−1 in reanalyses. The modeled zonal and meridional wind exhibit a too strong diurnal cycle, leading to a weak wind speed bias everywhere up to 5 km during daytime, turning into a too strong wind speed bias below 2 km at nighttime. The biases are fairly insensitive to the assimilation of sondes and likely related to remote convection and large scale pressure gradients. Convective momentum transport acts to distribute biases throughout the lowest 1.5 km, whereas at higher levels, other unresolved or dynamical tendencies play a role in setting the bias. Below 1 km, modelled friction due to unresolved physical processes appears too strong, but is (partially) compensated by dynamical tendencies, making this a challenging coupled problem.


MAUSAM ◽  
2021 ◽  
Vol 65 (4) ◽  
Author(s):  
SURYAK DUTTA ◽  
V.S. PRASAD ◽  
D. RAJAN

The Global Positioning System – Integrated Precipitable Water (IPW) data from Indian stations namely Chennai, Guwahati, Kolkata, Mumbai and New Delhi have been assimilated in the National Centre for Medium Range Weather Forecasting’s (NCMRWF) Global Data Assimilation System (GDAS). Gridpoint Statistical Interpolation (GSI) Scheme of GDAS analysis is experimented with the global model T254L64. The analyses and forecasts are carried out at triangular truncation of wave number 254 and with 64 levels in vertical. Global analyses are carried four times (0000 UTC, 0600 UTC, 1200 UTC and 1800 UTC) daily with intermittent time scheme. Model integrations are carried up to 168 hours. The present study examines the impact that integrated precipitable water has over various meteorological parameters. The study reveals that the assimilation of IPW data influences the analyses and corresponding forecasts of the weather model T254L64. This is an attempt of assimilation of IPW data of the aforesaid five Indian stations in the global model and examination of corresponding impact on various meteorological parameters over Indian region. It is seen that for the layers above 750 hPa the zonal and meridional wind components for IPW analyses have less biases. Forecasts from IPW simulations are found to have consistently by lower 850 hPa wind vector root mean square error (RMSE) where as at 250 hPa, improvement in IPW runs are seen only for day-1 and day-4 forecasts. For temperature at 850 hPa, IPW forecasts valid for day-4 & day-5 are better. At 250 hPa, temperature RMSE for IPW runs is lower for day-1 forecasts. Mean error of IPW forecasts at 250 hPa is lower for all the days of forecasts. Also, geo-potential RMSE for the IPW runs at 250 hPa is lower for all the days of forecasts. Forecasts vs analyses study shows positive impact of IPW assimilation on the anomaly and pattern correlations.


2021 ◽  
Author(s):  
Benedikt Gast ◽  
Ales Kuchar ◽  
Gunter Stober ◽  
Christoph Jacobi ◽  
Dimitry Pokhotelov ◽  
...  

<p class="western" align="justify"><span lang="en-GB">Previous studies that analysed the mesosphere and lower thermosphere (MLT) dynamics during sudden stratospheric warmings (SSWs) were limited only to particular SSWs or focused on a particular station representative only for some regions. Here we describe a comprehensive study of the average meteorological conditions during SSWs with a special focus on the general contribution of planetary (PW) and gravity (GW) waves as primary coupling mechanisms between lower and upper atmosphere. The average meteorological conditions in the MLT during SSWs were analyzed using a superposed epoch analysis (Denton et al., 2019) of meteor radar measurements for stations in the northern (NH: Collm, Kiruna, Sodankyla, CMOR) and the southern hemisphere (SH: Rio Grande, Davis, Rothera) for the altitude range of 80–100 km Using the adaptive spectral filtering method (Stober et al., 2021), we study in detail PW and GW characteristics in addition to measured zonal and meridional wind components in a time period from 2000 to 2020.</span></p> <p class="western" align="justify"><span lang="en-GB">In the NH the zonal wind is typically decreasing from around two weeks before the SSW onset, corresponding to an increased PW activity. Around the SSW onset, latitudinal differences in the zonal wind component as well as the PW activity can be seen. In the weeks before the SSW onset, the stations in the NH also show an increased level of GW kinetic energy. The meridional wind at the NH stations fluctuates with a periodicity of about 10 days before and around the onset. In contrast to previous studies (e.g. Yasui et al., 2016), the measurements in the SH are consistent with the inter-hemispheric coupling hypothesis. The expected downward shift of GW drag (Körnich and Becker, 2010) was reproduced by a downward travelling layer of enhanced GW activity at Davis and Rio Grande. Finally, the role of the terdiurnal tide in the GW energy composite is considered.</span></p>


2021 ◽  
Vol 19 ◽  
pp. 185-193
Author(s):  
Christoph Jacobi ◽  
Friederike Lilienthal ◽  
Dmitry Korotyshkin ◽  
Evgeny Merzlyakov ◽  
Gunter Stober

Abstract. Observations of upper mesosphere/lower thermosphere (MLT) wind have been performed at Collm (51.3∘ N, 13.0∘ E) and Kazan (56∘ N, 49∘ E), using two SKiYMET all-sky meteor radars with similar configuration. Daily vertical profiles of mean winds and tidal amplitudes have been constructed from hourly horizontal winds. We analyse the response of mean winds and tidal amplitudes to geomagnetic disturbances. To this end, we compare winds and amplitudes for very quiet (Ap ≤ 5) and unsettled/disturbed (Ap ≥ 20) geomagnetic conditions. Zonal winds in both the mesosphere and lower thermosphere are weaker during disturbed conditions for both summer and winter. The summer equatorward meridional wind jet is weaker for disturbed geomagnetic conditions. Tendencies for geomagnetic effects on mean winds over Collm and Kazan qualitatively agree during most of the year. For the diurnal tide, amplitudes in summer are smaller in the mesosphere and greater in the lower thermosphere, but no clear tendency is seen for winter. Semidiurnal tidal amplitudes increase during geomagnetic active days in summer and winter. Terdiurnal amplitudes are slightly reduced in the mesosphere during disturbed days, but no clear effect is visible for the lower thermosphere. Overall, while there is a noticeable effect of geomagnetic variability on the mean wind, the effect on tidal amplitudes, except for the semidiurnal tide, is relatively small and partly different over Collm and Kazan.


MAUSAM ◽  
2021 ◽  
Vol 47 (3) ◽  
pp. 275-280
Author(s):  
DHANNA SINGH ◽  
SUMAN GOYAL ◽  
C.V.V. BHADRAM ◽  
G. S. MANDAL

ABSTRACT. Based on 35 years' (1959-1993) data, the zonal and meridional wind components of selected Indian RS/RW statiomupto 100 hPa level were analysed for the pre-monsoon months of April and May in order to associate them with sub-regional monsoon rainfall of northeast India. Composite values of monsoon rainfall and meridional components for May for excess and deficient yean have revealed that anomaly of meridional components for the middle and upper troposphere is northerly/southerly preceding excees/deficient monsoon year. The meridional winds at most of the levels of Delhi and some of the levels of Jodhpur Nagpur, Bombay and Madras for the month of May showed significant correlations (significant at 0.1% to 5% level of significance) with sub-divisional monsoon rainfall in northeast India. The temporal behaviour of correlation coefficients for Punjab and Haryana for 16 and 20-year sliding windows has exhibited rasonable temporal stability except for first few years. Multiple rearession equations for 30 and 35 year period for Haryana, Punjab and contiguous northweat India were also developed. The regression model for Punjab sub-division has shown quite good  results for the independent period.  


Author(s):  
I. V. Dvoretska ◽  
M. V. Savenets ◽  
A. P. Umanets

The study presents the results of analysis of spatiotemporal distribution of updated total ozone climate normals for the period of 1991–2020. It analyzes the changes since the last total ozone climate normals estimate conducted for the period of 1981–2010. The daily data retrieved using TOMS and OMI satellite instruments over the territory of Ukraine allowed calculation of multiyear average values, climate normals for each day of the year, amplitudes, phases and determination coefficients for total ozone seasonal variations. Use of the NCEP/NCAR reanalysis data allowed establishment of the relation between total ozone and meridional wind changes in the lower stratosphere. The research shows the existence of the regions with higher/lower total ozone content that are not in line with the characteristics of latitudinal distribution. They are formed due to more frequent recurrence of air advection with ozone content that is not typical for the Ukrainian territory, mostly from January to March. The study describes a typical temporal distribution of the total ozone climate normals varying from 285 to 375 Dobson units (D.u.) and analyzes the statistic patterns of deviations distribution and recurrence of extremely high/low total ozone content. The paper emphasizes a small variation of total ozone over the territory of Ukraine. The authors also researched the features of spatial distribution of seasonal variation amplitudes varying within the range of 42–46 D.u. and the specifics of maximum values periods observed from 19 to 30 of March, depending on a region. It was established that, since the previous update of the climate normals, the total ozone decreased for all months with its maximum decrease of about 8 D.u. in winter. However, no increase of recurrence of ultraviolet radiation high levels was observed. Total ozone changes are mainly associated with shifts of meridional wind values to negative ones. This process indicates the increase of recurrence of air advection from the north. The paper also emphasizes the complexness of total ozone changes during the period of research and the lack of consistency of such changes with the circulation factor of summer months.


2021 ◽  
Author(s):  
Isabell Krisch ◽  
Neil P. Hindley ◽  
Oliver Reitebuch ◽  
Corwin J. Wright

Abstract. Since its launch in 2018, the European Space Agency’s Earth Explorer satellite Aeolus has provided global height resolved measurements of horizontal wind in the troposphere and lower stratosphere for the first time. Novel datasets such as these provide an unprecedented opportunity for the research of atmospheric dynamics and provide new insights into the dynamics of the upper troposphere and lower stratosphere (UTLS) region. Aeolus measures the wind component along its horizontal line-of-sight, but for the analysis and interpretation of atmospheric dynamics, zonal and/or meridional wind components are most useful. In this paper, we introduce and compare three different methods to derive zonal and meridional wind components from the Aeolus wind measurements. We find that the most promising method involves combining Aeolus measurements during ascending and descending orbits. Using this method, we derive global estimates of the zonal wind in the latitude range 79.7° S to 84.5° N with errors of less than 5 ms−1 (at the 2-sigma level). Due to the orbit geometry of Aeolus, the estimation of meridional wind in the tropics and at midlatitudes is more challenging and the quality is less reliable. However, we find that it is possible to derive meridional winds poleward of 70° latitude with absolute errors typically below ±5 ms−1 (at the 2-sigma level). This further demonstrate the value of Aeolus wind measurements for applications in weather and climate research, in addition to their important role in numerical weather prediction.


2021 ◽  
Author(s):  
Zixuan Jia ◽  
Ruth Doherty ◽  
Carlos Ordóñez ◽  
Chaofan Li ◽  
Oliver Wild ◽  
...  

Abstract. The influence of large-scale circulation on daily PM2.5 variability through its direct effect on key regional meteorological variables is examined over three major populated regions of China: Beijing–Tianjin–Hebei (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD). In BTH, a shallow East Asian trough curbs northerly cold and dry air from the Siberian High, enhancing PM2.5 pollution levels. Weak southerly winds in eastern and southern China, associated with a weakened Siberian High, suppress horizontal dispersion, contributing to air pollution accumulation over YRD. In PRD, weak southerly winds and precipitation deficits over southern China are conducive to high PM2.5 pollution levels. To account for these dominant large-scale circulation – PM2.5 relationships, we propose three new circulation-based indices for predicting different levels of air pollution based on regional PM2.5 concentrations in each region: a 500 hPa geopotential height-based index for BTH, a sea level pressure-based index for YRD and an 850 hPa meridional wind-based index for PRD. These three indices can effectively distinguish clean days from heavily polluted days in these regions, assuming variation is solely due to meteorology. We also find that including the most important regional meteorological variable in each region improves the performance of the circulation-based indices in predicting daily PM2.5 concentrations on the regional scale. These results are beneficial to understanding and forecasting the occurrence of heavily polluted PM2.5 days in BTH, YRD and PRD from a large-scale perspective.


Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1386
Author(s):  
Robin Wing ◽  
Milena Martic ◽  
Colin Triplett ◽  
Alain Hauchecorne ◽  
Jacques Porteneuve ◽  
...  

During a recent 2020 campaign, the Rayleigh lidar aboard the Bâtiment d’Essais et de Mesures (BEM) Monge conducted high-resolution temperature measurements of the upper Mesosphere and Lower Thermosphere (MLT). These measurements were used to conduct the first validation of ICON-MIGHTI temperatures by Rayleigh lidar. A double Mesospheric Inversion Layer (MIL) as well as shorter-period gravity waves was observed. Zonal and meridional wind speeds were obtained from locally launched radiosondes and the newly launched ICON satellite as well as from the European Centre for Medium-Range Weather Forecasts (ECMWF-ERA5) reanalysis. These three datasets allowed us to see the evolution of the winds in response to the forcing from the MIL and gravity waves. The wavelet analysis of a case study suggests that the wave energy was dissipated in small, intense, transient instabilities about a given wavenumber in addition to via a broad spectrum of breaking waves. This article will also detail the recent hardware advances of the Monge lidar that have allowed for the measurement of MILs and gravity waves at a resolution of 5 min with an effective vertical resolution of 926 m.


Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1284
Author(s):  
Zhao-Yu Chen ◽  
Yen-Hsyang Chu ◽  
Ching-Lun Su

Concurrent measurements of three-dimensional wind velocities made with three co-located wind profilers operated at frequencies of 52 MHz, 449 MHz, and 1.29 GHz for the period 12–16 September 2017 are compared for the first time in this study. The velocity–azimuth display (VAD) method is employed to estimate the wind velocities. The result shows that, in the absence of precipitation, the root mean square difference (RMSD) in the horizontal wind speed velocities U and wind directions D between different pairs of wind profilers are, respectively, in the range of 0.94–0.99 ms−1 and 7.7–8.3°, and those of zonal wind component u and meridional wind component v are in the respective ranges of 0.91–1.02 ms−1 and 1.1–1.24 ms−1. However, the RMSDs between wind profilers and rawinsonde are in the range of 2.89–3.26 ms−1 for horizontal wind speed velocity and 11.17–14.48° for the wind direction, which are around 2–3 factors greater than those between the wind profilers on average. In addition to the RMSDs, MDs between wind profilers and radiosonde are around one order of magnitude larger than those between wind profilers. These results show that the RMSDs, MDs, and Stdds between radars are highly consistent with each other, and they are much smaller than those between radar and rawinsonde. This therefore suggests that the wind profiler-measured horizontal wind velocities are much more reliable, precise, and accurate than the rawinsonde measurement.


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