Masaki Tsutsumi

A growing number of multistatic meteor radar networks are being established worldwide. The multistatic geometry with overlapping observation volumes of several meteor radars or passive receivers permits the inference of higher-order kinematic properties of the wind field or even the retrieval of arbitrary wind fields using tomographic algorithms. Furthermore, there is the long-standing question of the reliability of the vertical wind. In this study, we present a novel Volume Velocity Processing in spherical coordinates and perform an initial cross-comparison to previous implementations of the Volume Velocity Processing and the advanced 3DVAR+DIV retrieval. We performed a detailed climatological and multiyear comparison of mean winds, horizontal divergence, relative vorticity, stretching, and shearing deformation using observations of the Nordic Meteor Radar Cluster consisting of the meteor radars at Tromsø, Alta, Kiruna, and Sodankylä. Our results underscore that the spherical implementation of Volume Velocity Processing reduces/minimizes altitude-dependent biases caused by projection errors resulting from an incomplete representation of the observation geometry in the mean horizontal and vertical winds. All algorithms exhibit a very high correlation for the mean horizontal winds, but we found substantial differences in the vertical wind velocity and in the higher-order kinematic properties between the novel algorithm and previous versions of the Volume Velocity Processing. Furthermore, the novel algorithm reproduces a consistent seasonal pattern of the vertical velocity with upwelling during the hemispheric summer at the altitude of the zonal wind reversal and a corresponding but weaker downwelling during the winter months. The magnitudes of the vertical wind appear to be physically consistent with theoretically expected upward and downward motions and are on the order of a few cm s ⁻¹ . We also identified a scaling effect of the vertical wind in dependence on the temporal resolution and spatial averaging represented by a circle of influence in the new retrieval, which was confirmed by the measurement response of the 3DVAR+DIV retrieval. Wind data retrieved from SSVP and VVP are compared with the Japanese meteorological reanalysis known as JAWARA and SE-WACCM-X model data. The vertical wind patterns observed by the Nordic Meteor Radar Cluster show strong agreement between the two. Robust vertical wind retrievals obtained with a temporal resolution of 15–30 min and within a spatial domain of approximately 200–250 km centered between all meteor radars provide the best compromise between sampling density and spatial averaging for the Nordic Meteor Radar Cluster.

Continuous measurements of vertical wind in the mesosphere and lower thermosphere are rare and technically challenging. However, multistatic meteor radar networks, such as the Nordic Meteor Radar Cluster, offer a unique opportunity to use advanced tomographic wind retrieval methods to determine neutral winds, including vertical wind components. The Spherical Volume Velocity Processing technique is a newly developed tomographic algorithm that enables the extraction of Doppler-based vertical winds and the computation of vertical winds from horizontal divergence through vertical integration. In this study, we present an intercomparison of various vertical wind retrieval methods to evaluate remaining biases and to quantify the magnitude of summer mesospheric vertical upwelling and corresponding downwelling. The retrieved wind data are compared with the Japanese meteorological reanalysis known as JAWARA, as well as a year of free-running SE-WACCM-X model data. Our findings indicate a strong agreement concerning the seasonal patterns of horizontal winds between the Nordic Meteor Radar Cluster and both models. The observed vertical wind velocities range from 2 to 15 cm/s. Additionally, measurements from the Nordic Meteor Radar Cluster show cooling and heating rates of -40 to 100 K/day during summer and 5 to 20 K/day in the winter months.

Continuous measurements of vertical wind in the mesosphere and lower thermosphere are rare and technically challenging. However, multistatic meteor radar networks, such as the Nordic Meteor Radar Cluster, offer a unique opportunity to use advanced tomographic wind retrieval methods to determine neutral winds, including vertical wind components. The Spherical Volume Velocity Processing technique is a newly developed tomographic algorithm that enables the extraction of Doppler-based vertical winds and the computation of vertical winds from horizontal divergence through vertical integration. In this study, we present an intercomparison of various vertical wind retrieval methods to evaluate remaining biases and to quantify the magnitude of summer mesospheric vertical upwelling and corresponding downwelling. The retrieved wind data are compared with the Japanese meteorological reanalysis known as JAWARA, as well as a year of free-running SE-WACCM-X model data. Our findings indicate a strong agreement concerning the seasonal patterns of horizontal winds between the Nordic Meteor Radar Cluster and both models. The observed vertical wind velocities range from 2 to 15 cm/s. Additionally, measurements from the Nordic Meteor Radar Cluster show cooling and heating rates of -40 to 100 K/day during summer and 5 to 20 K/day in the winter months.

A global climatology of diurnal tides in the mesosphere and lower thermosphere (MLT) is constructed using multiyear observations from fifteen meteor radars distributed worldwide. The results show that diurnal tidal amplitudes are strongest at low and mid-latitudes (10–50° N/S), with peak values of about 60 m s ⁻¹ near 20–30° N/S, and are comparatively weak near the Equator and at polar latitudes. The seasonal variations of the diurnal tide are characterized by maxima around the equinoxes and minima during the solstices. In addition to these global climatological features, we identify a clear modulation of the vertical structure of diurnal tidal amplitude and phase by seasonal variations in solar forcing, represented here by the solar zenith angle (SZA). This modulation is particularly evident at northern low and mid-latitudes, but is much weaker in the Southern Hemisphere. The hemispheric asymmetry suggests that the tidal response to solar forcing is not globally uniform. To further explore the possible cause of this asymmetry, we examine the meridional fluxes of zonal tidal momentum. The results suggest that background zonal winds can influence tidal propagation through filtering effects and momentum drag, thereby contributing to the observed hemispheric differences in tidal structure. These results provide new observational evidence for the coupling between solar forcing and diurnal tides in the MLT region and offer useful constraints for the evaluation of general circulation models. They also improve our understanding of tidal propagation and variability in the middle and upper atmosphere.

The 2018–2019 sudden stratospheric warming (SSW) is simulated using a high‐resolution whole atmosphere model that includes interactive chemistry and constrained meteorology. The simulations are performed using a high‐resolution (∼0.25) configuration of the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) with the meteorology constrained up to ∼10 hPa using ECMWF Reanalysis v5 (ERA5). The high‐resolution WACCM‐X simulations are compared to satellite and ground‐based observations as well as two whole atmosphere data assimilation systems. Based on these comparisons, the high‐resolution WACCM‐X simulations are shown to alleviate two long‐standing biases in low‐resolution (∼2) WACCM‐X: a westward wind bias in the mesosphere and lower thermosphere (MLT) at wintertime high‐latitudes, and insufficient downward transport of nitric oxide (NO) following SSWs. The high‐resolution simulations are also able to capture much of the day‐to‐day variability in MLT winds seen in meteor radar observations. The simulations represent the first meteorologically constrained high‐resolution whole atmosphere simulations with fully interactive chemistry, and demonstrate that high‐resolution whole atmosphere model simulations can significantly improve representation of dynamical and chemical variability in the middle and upper atmosphere during SSWs.

A global climatology of diurnal tides in the mesosphere and lower thermosphere (MLT) is constructed using multiyear observations from fifteen meteor radars distributed worldwide. The results show that diurnal tidal amplitudes are strongest at low and mid-latitudes (10°–50° N/S), with peak values of about 60 m s^-1 near 20°–30° N/S, and are comparatively weak near the Equator and at polar latitudes. The seasonal variations of the diurnal tide are characterized by maxima around the equinoxes and minima during the solstices. In addition to these global climatological features, we identify a clear modulation of the vertical structure of diurnal tidal amplitude and phase by seasonal variations in solar forcing, represented here by the solar zenith angle (SZA). This modulation is particularly evident at northern low and mid-latitudes, but is much weaker in the Southern Hemisphere. The hemispheric asymmetry suggests that the tidal response to solar forcing is not globally uniform. To further explore the possible cause of this asymmetry, we examine the meridional fluxes of zonal tidal momentum. The results suggest that background zonal winds can influence tidal propagation through filtering effects and momentum drag, thereby contributing to the observed hemispheric differences in tidal structure. These results provide new observational evidence for the coupling between solar forcing and diurnal tides in the MLT region and offer useful constraints for the evaluation of general circulation models. They also improve our understanding of tidal propagation and variability in the middle and upper atmosphere.

A growing number of multistatic meteor radar networks are being established worldwide. The multistatic geometry with overlapping observation volumes of several meteor radars or passive receivers permits the inference of higher-order kinematic properties of the wind field or even the retrieval of arbitrary wind fields using tomographic algorithms. Furthermore, there is the long-standing question of the reliability of the vertical wind. In this study, we present a novel Volume Velocity Processing in spherical coordinates and perform an initial cross-comparison to previous implementations of the Volume Velocity Processing and the advanced 3DVAR+DIV retrieval. We performed a detailed climatological and multiyear comparison of mean winds, horizontal divergence, relative vorticity, stretching, and shearing deformation using observations of the Nordic Meteor Radar Cluster consisting of the meteor radars at Tromsø, Alta, Kiruna, and Sodankylä. Our results underscore that the spherical implementation of Volume Velocity Processing reduces/minimizes altitude-dependent biases caused by projection errors resulting from an incomplete representation of the observation geometry in the mean horizontal and vertical winds. All algorithms exhibit a very high correlation for the mean horizontal winds, but we found substantial differences in the vertical wind velocity and for the higher-order kinematic properties between the novel algorithm compared to previous versions of the Volume Velocity Processing. Furthermore, the novel algorithm reproduces a consistent seasonal pattern of the vertical velocity with upwelling during the hemispheric summer at the altitude of the zonal wind reversal and a corresponding but weaker downwelling during the winter months. The magnitudes of the vertical wind appear to be physically consistent with theoretically expected upward and downward motions and are in the order of a few cm/s. We also identified a scaling effect of the vertical wind in dependence on the temporal resolution and spatial averaging represented by a circle of influence in the new retrieval, which was confirmed by the measurement response of the 3DVAR+DIV retrieval. The most reliable vertical winds were obtained for a temporal resolution of 15–30 minutes and a spatial domain of about 200–250 km centered between all meteor radars of the Nordic Meteor Radar Cluster.

A global climatology of diurnal tides in the mesosphere and lower thermosphere (MLT) is constructed using multiyear observations from fifteen meteor radars distributed worldwide. The results show that diurnal tidal amplitudes are strongest at low and mid-latitudes (10°–50° N/S), with peak values of about 60 m s^-1 near 20°–30° N/S, and are comparatively weak near the Equator and at polar latitudes. The seasonal variations of the diurnal tide are characterized by maxima around the equinoxes and minima during the solstices. In addition to these global climatological features, we identify a clear modulation of the vertical structure of diurnal tidal amplitude and phase by seasonal variations in solar forcing, represented here by the solar zenith angle (SZA). This modulation is particularly evident at northern low and mid-latitudes, but is much weaker in the Southern Hemisphere. The hemispheric asymmetry suggests that the tidal response to solar forcing is not globally uniform. To further explore the possible cause of this asymmetry, we examine the meridional fluxes of zonal tidal momentum. The results suggest that background zonal winds can influence tidal propagation through filtering effects and momentum drag, thereby contributing to the observed hemispheric differences in tidal structure. These results provide new observational evidence for the coupling between solar forcing and diurnal tides in the MLT region and offer useful constraints for the evaluation of general circulation models. They also improve our understanding of tidal propagation and variability in the middle and upper atmosphere.

Continuous measurements of vertical wind in the mesosphere and lower thermosphere are rare and technically challenging. However, multistatic meteor radar networks, such as the Nordic Meteor Radar Cluster, offer a unique opportunity to use advanced tomographic wind retrieval methods to determine neutral winds, including vertical wind components. The Spherical Volume Velocity Processing technique is a newly developed tomographic algorithm that enables the extraction of Doppler-based vertical winds and the computation of vertical winds from horizontal divergence through vertical integration.In this study, we present an intercomparison of various vertical wind retrieval methods to evaluate remaining biases and to quantify the magnitude of summer mesospheric vertical upwelling and corresponding downwelling. The retrieved wind data are compared with the Japanese meteorological reanalysis known as JAWARA, as well as a year of free-running SE-WACCM-X model data. Our findings indicate a strong agreement concerning the seasonal patterns of horizontal winds between the Nordic Meteor Radar Cluster and both models. The observed vertical wind velocities range from 2 to 15 cm/s. Additionally, measurements from the Nordic Meteor Radar Cluster show cooling and heating rates of -40 to 100 K/day during summer and 5 to 20 K/day in the winter months.

A growing number of multistatic meteor radar networks are being established worldwide. The multistatic geometry with overlapping observation volumes of several meteor radars or passive receivers permits the inference of higher-order kinematic properties of the wind field or even the retrieval of arbitrary wind fields using tomographic algorithms. Furthermore, there is the long-standing question of the reliability of the vertical wind. In this study, we present a novel Volume Velocity Processing in spherical coordinates and perform an initial cross-comparison to previous implementations of the Volume Velocity Processing and the advanced 3DVAR+DIV retrieval. We performed a detailed climatological and multiyear comparison of mean winds, horizontal divergence, relative vorticity, stretching, and shearing deformation using observations of the Nordic Meteor Radar Cluster consisting of the meteor radars at Tromsø, Alta, Kiruna, and Sodankylä. Our results underscore that the spherical implementation of Volume Velocity Processing reduces/minimizes altitude-dependent biases caused by projection errors resulting from an incomplete representation of the observation geometry in the mean horizontal and vertical winds. All algorithms exhibit a very high correlation for the mean horizontal winds, but we found substantial differences in the vertical wind velocity and for the higher-order kinematic properties between the novel algorithm compared to previous versions of the Volume Velocity Processing. Furthermore, the novel algorithm reproduces a consistent seasonal pattern of the vertical velocity with upwelling during the hemispheric summer at the altitude of the zonal wind reversal and a corresponding but weaker downwelling during the winter months. The magnitudes of the vertical wind appear to be physically consistent with theoretically expected upward and downward motions and are in the order of a few cm/s. We also identified a scaling effect of the vertical wind in dependence on the temporal resolution and spatial averaging represented by a circle of influence in the new retrieval, which was confirmed by the measurement response of the 3DVAR+DIV retrieval. The most reliable vertical winds were obtained for a temporal resolution of 15–30 minutes and a spatial domain of about 200–250 km centered between all meteor radars of the Nordic Meteor Radar Cluster.