Reconstructing 4D Wind Fields from Radar Observations using Machine Learning

Simultaneous optical and meteor head echo measurements using the Middle Atmosphere Alomar Radar System (MAARSY): Data collection and preliminary analysis

Abstract. The ECOMA (Existence of Charge state Of meteoric smoke particles in the Middle Atmosphere) sounding rocket campaign was conducted during the Geminid meteor shower in December 2010 in order to explore whether there is a change of the properties of meteoric smoke particles due to the stream. In parallel to the rocket flights, three radars monitored the Geminid activity located at the launch site in Northern Norway and in Northern Germany to gain information about the meteor flux into the atmosphere. The results presented here are based on specular meteor radar observations measuring the radiant position, the velocity and the meteor flux into the atmosphere during the Geminids. Further, the MAARSY (Middle Atmosphere Alomar Radar System) radar was operated to conduct meteor head echo experiments. The interferometric capabilities of MAARSY permit measuring the meteor trajectories within the radar beam and to determine the source radiant and geocentric meteor velocity, as well as to compute the meteor orbit.

One of the main factors characterizing the dynamics of the atmosphere is its vertical density stratification. Gravity waves arising under these conditions play an essential role in large-scale energy transport through upwards propagation and breaking in the middle atmosphere, manifesting in phenomena such as the cold summer mesopause. Moreover, it was recently found that the summer mesopause is also home to the strongly stratified turbulence regime occurring at extremely high buoyancy Reynolds and low horizontal Froude numbers. Direct observation or numerical simulation of these processes with high resolution proves difficult however, due to the remoteness of the region combined with the mesoscale horizontal and small vertical scales that have to be resolved for a detailed analysis of the emerging dynamics. To deepen our knowledge of the these processes in this region, we employ a combined approach of state-of-the-art radar observations using the MAARSY and SIMONe systems and the physics-informed machine learning method HYPER. The first step and the main topic of the current study is to reconstruct high-resolution 3D wind fields from the line-of-sight measurements in the summer mesosphere. The resulting fields closely capture the observed data and produce high-fidelity, Navier-Stokes-compliant predictions of the surrounding flow beyond measuring points. Building on this, we aim to provide an analysis of the first high-resolution radar observations of strongly stratified turbulence in the middle atmosphere.

In the present study, we analyzed the wind measurements in the troposphere and lower stratosphere over Andya in northern Norway (69.30N, 16.04E) with the Middle Atmosphere Alomar Radar System (MAARSY) from 2017 to 2020.We calculated the momentum flux and vertical wind power spectra using the fast Fourier transformation (FFT) analysis technique.The spectra are characterized into different regions based on: frequency (lower and higher than (13 h) -1 , since the local inertial period over Andya is 13 h), altitudes (lower troposphere, middle troposphere, tropopause region, and lower stratosphere), and seasons (spring, summer, autumn, and winter).We report for the first time that both the momentum flux spectra and vertical wind power spectra display a seasonal and altitudinal variation with the minimum in summer and the maximum magnitude in the troposphere.We also studied the intermittency of the waves during this period using the Gini coefficient over Northern Norway for the first time, which is used to distinguish the intermittent wave periodicities from the non-intermittent ones.We reveal that the high-frequency (short-period oscillations) gravity waves are more intermittent than the low-frequency (longperiod oscillations).Additionally, the most intermittent waves are located in the lower stratospheric altitudes for low-frequency waves, while the high-frequency waves are dominantly intermittent in the whole altitude region with small patches of lower intermittency region.

We present the first and direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes (PMWE) simultaneously observed by the conjugate observation with Arase satellite and high‐power atmospheric radars in both hemispheres, namely, the Program of the Antarctic Syowa Mesosphere, Stratosphere, and Troposphere/Incoherent Scatter Radar at Syowa Station (SYO; −69.00°S, 39.58°E), Antarctica, and the Middle Atmosphere Alomar Radar System at Andøya (AND; 69.30°N, 16.04°E), Norway. The PMWE were observed during 03–07 UT on 21 March 2017, just after the arrival of corotating interaction region in front of high‐speed solar wind stream. An isolated substorm occurred at 04 UT during this interval. Electromagnetic ion cyclotron (EMIC) waves and whistler mode chorus waves were simultaneously observed near the magnetic equator and showed similar temporal variations to that of the PMWE. These results indicate that chorus waves as well as EMIC waves are drivers of precipitation of energetic electrons, including relativistic electrons, which make PMWE detectable at 55‐ to 80‐km altitude. Cosmic noise absorption measured with a 38.2‐MHz imaging riometer and low‐altitude echoes at 55–70 km measured with an medium‐frequency radar at SYO also support the relativistic electron precipitation. We suggest a possible scenario in which the various phenomena observed in near‐Earth space, such as magnetospheric plasma waves (EMIC waves and chorus waves), pulsating auroras, cosmic noise absorption, and PMWE, can be explained by the interaction between the high‐speed solar wind containing corotating interaction regions and the magnetosphere.

Abstract. The mesosphere and lower thermosphere (MLT) region represents a captivating yet challenging field of research. Remote sensing techniques, such as radar, have proven invaluable for investigating this domain. The Middle Atmosphere Alomar Radar System (MAARSY), located in northern Norway (69∘ N, 16∘ E), uses polar mesospheric summer echoes (PMSEs) as tracers to study MLT dynamics across multiple scales. Chau et al. (2021) recently discovered a spatiotemporally highly localized event showing a varicose mode (simultaneous upward and downward movements), which is characterized by extreme vertical velocities (|w|≥3σ) of up to 60 m s−1 in the vertical drafts. Motivated by this finding, our objective is to identify and quantify similar extreme events or comparable varicose structures, i.e., defined by quasi-simultaneous updrafts and downdrafts, that may have been previously overlooked or filtered out. To achieve this, we conducted a thorough manual search through a MAARSY dataset, considering the PMSE months (i.e., May, June, July, August) spanning from 2015 to 2021. This search has revealed that these structures do indeed occur relatively frequently with an occurrence rate of up to 2.5 % per month. Over the 7-year period, we observed and recorded more than 700 varicose-mode events with a total duration of about 265 h and documented their vertical extent, vertical velocity characteristics, duration, and their occurrence behavior. Remarkably, these events manifest throughout the entire PMSE season with pronounced occurrence rates in June and July, while the probability of their occurrence decreases towards the beginning and end of the PMSE seasons. Furthermore, their diurnal variability aligns with that of PMSEs. On average, the observed events persisted for 20 min, while the varicose mode caused an average expansion of the PMSE layer by a factor of 1.5, with a maximum vertical expansion averaging around 8 km. Notably, a careful examination of the vertical velocities associated with these events confirmed that approximately 17 % surpassed the 3σ threshold, highlighting their non-Gaussian velocity distribution and extreme nature.

Simulating whole atmosphere dynamics, chemistry, and physics is computationally expensive. It can require high vertical resolution throughout the middle and upper atmosphere, as well as a comprehensive chemistry and aerosol scheme coupled to radiation physics. An unintentional outcome of the development of one of the most sophisticated and hence computationally expensive model configurations is that it often excludes a broad community of users with limited computational resources. Here, we analyze two configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) with simplified “middle atmosphere” chemistry at nominal 1 and 2° horizontal resolutions. Using observations, a reanalysis, and direct model comparisons, we find that these configurations generally reproduce the climate, variability, and climate sensitivity of the 1° nominal horizontal resolution configuration with comprehensive chemistry. While the background stratospheric aerosol optical depth is elevated in the middle atmosphere configurations as compared to the comprehensive chemistry configuration, it is comparable among all configurations during volcanic eruptions. For any purposes other than those needing an accurate representation of tropospheric organic chemistry and secondary organic aerosols, these simplified chemistry configurations deliver reliable simulations of the whole atmosphere that require 35% and 86% fewer computational resources at nominal 1 and 2° horizontal resolution, respectively.

Liu, X.; Wang, Q.; Liu, C.; He, C.; Wang, S.; Hou, P.; Zhu, X., and Wu, Z., 2020. Wind field reconstruction and analysis of super typhoon Mangkhut (1822). In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 151–157. Coconut Creek (Florida), ISSN 0749-0208.This paper reports the research conducted on wind field reconstruction for super typhoon Mangkhut (1822), which occurred in 2018/09. The performances of two common methods, i.e., the parametric typhoon model and CCMP reanalysis data, for the hindcasting of typhoon wind fields are examined, and an improved method is then proposed, which avoids the radius effect in the traditional superposition method. The proposed method relies on a combination of CCMP reanalysis data and parametric wind field results and directly evaluates the maximum wind speed. Moreover, the central difference method is employed to smooth the transitional area. This method notably improves the hindcasting of typhoon wind fields, and its capability is calibrated by field data from buoy platforms in the Pearl River Estuary. Finally, certain typical parameters, such as the wind field, wind speed and wind stress curl, during super typhoon Mangkhut are determined and analyzed.

Background 2. Critique Recently, an article by Oliver et al. [1994], subsequently referred to as OEA, described studies of gravity waves at ionospheric heights based on observations with the middle and upper atmosphere (MU) radar.That facility is extremely capable and promises to greatly enhance the study of traveling ionospheric disturbances (TIDs) associated with acoustic-gravity waves (AGWs) in the thermosphere.However, the particular approach used by OEA strikes this correspondent as susceptible to pitfalls, and he is compelled to question certain of OEA's conclusions.zontal lines indicate altitude in 100-km steps.Superposed on the beam layout is a hypothetical oblique-plane-wave electron-density perturbation in the altitude range 200-400 km.Dark solid oblique traces indicate positive-maximum perturbations.Dark dashed oblique traces indicate alternate half cycles.The trace wavelength of the hypothetical electrondensity structure drawn in the E-W plane is A EW = 100 km.Continually referring to Figure 1 (and to figures in OEA), we treat several concerns successively.

The interaction of airflow with complex terrain has the potential to significantly amplify extreme precipitation events and modify the structure and intensity of precipitating cloud systems. However, understanding and forecasting such events is challenging, in part due to the scarcity of direct in situ measurements. Doppler radar can provide the capability to monitor extreme rainfall events over land, but our understanding of airflow modulated by orographic interactions remains limited. The SAMURAI software is a three-dimensional variational data assimilation (3DVAR) technique that uses the finite element approach to retrieve kinematic and thermodynamic fields. The analysis has high fidelity to observations when retrieving flows over a flat surface, but the capability of imposing topography as a boundary constraint is not previously implemented. Here, we implement the immersed boundary method (IBM) as pseudo-observations at their native coordinates in SAMURAI to represent the topographic forcing and surface impermeability. In this technique, neither data interpolation onto a Cartesian grid nor explicit physical constraint integration during the cost function minimization is needed. Furthermore, the physical constraints are treated as pseudo-observations, offering the flexibility to adjust the strength of the boundary condition. A series of observing simulation sensitivity experiments (OSSEs) using a full-physics model and radar emulator simulating rainfall from Typhoon Chanthu (2021) over Taiwan are conducted to evaluate the retrieval accuracy and parameter settings. The OSSE results show that the strength of the IBM constraints can impact the overall wind retrievals. Analysis from real radar observations further demonstrates that the improved retrieval technique can advance scientific analyses for the underlying dynamics of orographic precipitation using radar observations.

Abstract. A comparative study of the quasi-16-day wave (QSDW) in the middle atmosphere using meteor radar observations and reanalysis data from three Brazilian stations, Sao Joao do Cariri (7.4° S, 36.5° W) (CA), Cachoeira Paulista (22.7° S, 45° W) (CP), and Santa Maria (29.7° S, 53.7° W) (SM) has been carried out in the year 2005 to delineate its latitudinal variability characteristics. The broad spectral behavior around 16-day periodicity may indicate multiple modes of the concerned wave component. The wave amplitude shows a number of peaks over the year with the largest one in summer and winter in the case of mesosphere–lower thermosphere (MLT) and stratosphere, respectively. A potential coupling of the concerned wave with other short period planetary waves, especially at CA and CP is evinced. Although zonal propagation exhibits both eastward as well as westward waves there is a general preference of eastward waves at mid-latitude and westward waves at tropical latitudes. The prevailing westerly background wind in the middle atmosphere is conceived to favor the wave filtering of westward propagating Rossby waves at lower latitude.

The measurement of temperature in the middle atmosphere with Rayleigh-scatter lidars is an important technique for assessing atmospheric change. Current retrieval schemes for this temperature have several shortcomings, which can be overcome by using an optimal estimation method (OEM). Forward models are presented that completely characterize the measurement and allow the simultaneous retrieval of temperature, dead time, and background. The method allows a full uncertainty budget to be obtained on a per profile basis that includes, in addition to the statistical uncertainties, the smoothing error and uncertainties due to Rayleigh extinction, ozone absorption, lidar constant, nonlinearity in the counting system, variation of the Rayleigh-scatter cross section with altitude, pressure, acceleration due to gravity, and the variation of mean molecular mass with altitude. The vertical resolution of the temperature profile is found at each height, and a quantitative determination is made of the maximum height to which the retrieval is valid. A single temperature profile can be retrieved from measurements with multiple channels that cover different height ranges, vertical resolutions, and even different detection methods. The OEM employed is shown to give robust estimates of temperature, which are consistent with previous methods, while requiring minimal computational time. This demonstrated success of lidar temperature retrievals using an OEM opens new possibilities in atmospheric science for measurement integration between active and passive remote sensing instruments.

Abstract. Motivated by an improved European Space Agency (ESA) version of calibrated Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) spectra (version 8.03), we have released version 8 of MIPAS temperatures and pointing information retrieved from 2005–2012 MIPAS measurements at 12–15 µm in the Middle Atmosphere (MA), Upper Atmosphere (UA) and Noctilucent Cloud (NLC) measurement modes. The Institute of Meteorology and Climate Research–Instituto de Astrofisica de Andalucia (IMK–IAA) retrieval processor in use considers non-local thermodynamic equilibrium (non-LTE) emission explicitly for each limb scan. This non-LTE treatment is essential to obtain accurate temperatures above the mid-mesosphere because at the altitudes covered, up to 115 km, the simplified climatology-based non-LTE treatment employed for the Nominal (NOM) measurements is insufficient. Other updates in MA/UA/NLC version 8 non-LTE temperature retrievals from previous data releases include more realistic atomic oxygen and carbon dioxide abundances, an updated set of spectroscopic data, an improved spectral shift retrieval, a continuum retrieval extended to altitudes up to 58 km, consideration of an altitude-dependent radiance offset retrieval, the use of wider microwindows above 85 km to capture the offset, an improved accuracy in forward model calculations, new a priori temperature information, improved temperature horizontal gradient retrievals and the use of MIPAS version 5 interfering species where available. The resulting MIPAS MA/UA/NLC IMK–IAA temperature dataset is reliable for scientific analysis in the full measurement vertical range for the MA (18–102 km) and the NLC (39–102 km) observations and from 42 to 115 km for the UA observations. The random temperature errors, dominated by the instrumental noise, are typically less than 1 K below 60 km, 1–3 K at 60–70 km, 3–5 K at 70–90 km, 6–8 K at 90–100 km, 8–12 K at 100–105 km and 12–20 K at 105–115 km. Random pointing correction errors, also mainly arising from instrumental noise, are on average 50 m for tangent altitudes up to 60 km and decrease linearly to values smaller than 20 m for altitudes above 95 km. The vertical resolution is 3 km at altitudes below 50 km, 3–5 km at 50–70 km, 4–6 km at 70–90 km, 6–10 km at 90–100 km and 8–11 km at 100–115 km. The systematic errors in retrieved temperatures below 75 km are driven by uncertainties in the CO2 spectroscopic data and, above 80 km, by uncertainties in the non-LTE model parameters (including collisional rates and atomic oxygen abundance) and the CO2 abundance. These lead to systematic temperature errors of less than 0.7 K below 55 km, 1 K at 60–80 km, 1–2 K at 80–90 km, 3 K at 95 km, 6–8 K at 100 km, 10–20 K at 105 km and 20–30 K at 115 km. Systematic errors in the tangent altitude correction, mainly arising from CO2 spectroscopic uncertainties, are 250 m at 20 km, 200 m at 40–60 km, 100 m at 80 km and smaller than 50 m above 90 km. The consistency between the MA/UA/NLC and the NOM IMK–IAA datasets is excellent below 70 km (typical 0.5–1 K differences). The comparison of this temperature dataset with co-located Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements shows excellent agreement, with differences typically within 1.5 K below 90 km, 1–3 K at 90–95 km, 1–5 K at 95–100 km, 1–8 K at 100–105 km and 1–10 K above. The agreement with SABER improves with respect to previous MIPAS IMK–IAA data versions.

A three-dimensional chemical transport model(CTM) was developed at the Meteorological Research Institute by coupling a chemical module with the MJ98 general circulation model (dynamical module) for the study of stratospheric chemistry.This model, MJ98-CTM, ran for approximately 15 years and the simulated chemical species were investigated, focusing on the time-mean fields. The chemical module was based on the family method and contains major stratospheric species, i.e., 34 long-lived species including 7 families and 15 short-lived species with 79 gas phase reactions and 34 photodissociations. Two types (I and II) of polar stratospheric clouds (PSCs) and sulfate aerosols were included with six heterogeneous reactions on PSCs and three heterogeneous reactions on sulfate aerosols. MJ98-CTMs of T21L45 and T42L45 versions were integrated using climatological monthly mean values of sea-surface temperature and ozone for the dynamical module, and fixed values at the surface for surface-origin species in the chemical module. Radiatively active gases such as ozone, methane, and nitrous oxide were not treated interactively between the two modules. Horizontal resolutions were 5.6°(∼600 km) for the T21 model and 2.8°(∼300 km) for the T42 model. The vertical resolution L45 had a vertical spacing of about 2 km in the stratosphere with a top at 0.01 hPa (80km). Qualitatively, MJ98-CTM suitably reproduced the temporal and spatial features of observed ozone and other chemical species in the middle atmosphere. However, the lower stratosphere held crucial errors for the distributions of chemical species, particularly ozone, yielding positive errors for column ozone. A major cause of these errors can be ascribed to the errors associated with transport: one based on the wind field bias produced by MJ98, and the other from the coarse vertical resolution.

Long‐term measurements from several lidar instruments (Rayleigh and sodium) located at 44.0°N, 40.6°N, 34.4°N, and 19.5°N have been used to develop a new climatology of the middle atmosphere temperature. For each instrument, the measurements on every individual day of the year over the entire long‐term record were averaged to build a composite year of temperature profiles. These profiles were then interpolated to provide temperature values at 1‐km altitude intervals so that the climatology comprises daily temperature values at integer altitudes between 15 and 110 km, depending on the instrument. The climatologies for each lidar were then compared to the CIRA‐86 model and to each other. Large differences between the lidar temperatures and the CIRA‐86 temperatures are identified and explained. When compared to all instruments, CIRA‐86 appears systematically much too cold between 90 and 95 km, by 20 K or more, and possibly 6–8 K too warm around 80 km, making its use as a reference atmosphere model questionable at these altitudes. The annual and semiannual components of the seasonal variability and the 2‐ to 33‐day period variability were investigated. An annual cycle with 6–7 K amplitude in the upper stratosphere, increasing to 15–20 K at 80 km, is observed at midlatitudes. This cycle is in phase with the solar flux in the stratosphere and in opposite phase in the mesosphere with a very cold summer mesopause at 85 km, in good agreement with previous climatologies. At lower latitudes, a semiannual oscillation propagates downward from 85 to 30 km and is characterized by a stronger first cycle than the second (4 and 2 K amplitude respectively). The 2‐ to 33‐day variability at midlatitudes shows a maximum during winter around 40 km and in the mésosphère. The first peak is associated with planetary wave activity and stratospheric warmings and the second to the occurrence of mesospheric temperature inversions. Finally, sudden seasonal transitions, highly consistent between all instruments, have been observed. In particular, in the early winter midlatitudes a two‐step warming of the winter mésosphère between 65 and 85 km as well as a cooling of the lower mésosphère appear to be real climatological events rather than some short‐term geophysical or instrumental random variability.