Warming In December Research Articles

Atmospheric tomography using the Nordic Meteor Radar Cluster and Chilean Observation Network De Meteor Radars: network details and 3D-Var retrieval

Abstract. Ground-based remote sensing of atmospheric parameters is often limited to single station observations by vertical profiles at a certain geographic location. This is a limiting factor for investigating gravity wave dynamics as the spatial information is often missing, e.g., horizontal wavelength, propagation direction or intrinsic frequency. In this study, we present a new retrieval algorithm for multistatic meteor radar networks to obtain tomographic 3-D wind fields within a pre-defined domain area. The algorithm is part of the Agile Software for Gravity wAve Regional Dynamics (ASGARD) and called 3D-Var, and based on the optimal estimation technique and Bayesian statistics. The performance of the 3D-Var retrieval is demonstrated using two meteor radar networks: the Nordic Meteor Radar Cluster and the Chilean Observation Network De Meteor Radars (CONDOR). The optimal estimation implementation provide statistically sound solutions and diagnostics from the averaging kernels and measurement response. We present initial scientific results such as body forces of breaking gravity waves leading to two counter-rotating vortices and horizontal wavelength spectra indicating a transition between the rotational k−3 and divergent k-5/3 mode at scales of 80–120 km. In addition, we performed a keogram analysis over extended periods to reflect the latitudinal and temporal impact of a minor sudden stratospheric warming in December 2019. Finally, we demonstrate the applicability of the 3D-Var algorithm to perform large-scale retrievals to derive meteorological wind maps covering a latitude region from Svalbard, north of the European Arctic mainland, to central Norway.

Effect of atmospheric circulation on recent temperature changes in Finland

The effect of atmospheric circulation on temperature variability and trends in Finland in 1979–2018 is studied using a trajectory-based method. On the average 81% of the detrended interannual variance of monthly mean temperatures is explained by the start points of the three-dimensional trajectories, with the best performance in autumn and winter. Atmospheric circulation change is only found to have had a small impact on the observed annual mean temperature trends, but it has considerably modified the trends in individual months. In particular, changes in circulation explain the lack of observed warming in June, the very modest warming in October in southern Finland, and about a half of the very large warming in December. The residual trends obtained by subtracting the circulation-related change from observations are robustly positive in all months of the year, exhibit a smoother seasonal cycle, and agree better with the multi-model mean temperature trends from models in the 5th Coupled Model Intercomparison Project (CMIP5). Nevertheless, some differences between the residual trends and the average CMIP5 trends are also found.

Observations of filamentary structures near the vortex edge in the Arctic winter lower stratosphere

Abstract. The CRISTA-NF (Cryogenic Infrared Spectrometers and Telescope for the Atmosphere – New Frontiers) instrument is an airborne infrared limb sounder operated aboard the Russian research aircraft M55-Geophysica. The instrument successfully participated in a large Arctic aircraft campaign within the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) project in Kiruna (Sweden) from January to March 2010. This paper concentrates on the measurements taken during one flight of the campaign, which took place on 2 March in the vicinity of the polar vortex. We present two-dimensional cross-sections of derived volume mixing ratios for the trace gases CFC-11, O3, and ClONO2 with an unprecedented vertical resolution of about 500 to 600 m for a large part of the observed altitude range (≈ 6–19 km) and a dense horizontal sampling along flight direction of ≈ 15 km. The trace gas distributions show several structures, for example a part of the polar vortex and a vortex filament, which can be identified by means of O3–CFC-11 tracer–tracer correlations. The observations made during this flight are interpreted using the chemistry and transport model CLaMS (Chemical Lagrangian Model of the Stratosphere). Comparisons of the observations with the model results are used to assess the performance of the model with respect to advection, mixing, and the chemistry in the polar vortex. These comparisons confirm the capability of CLaMS to reproduce even very small-scale structures in the atmosphere, which partly have a vertical extent of only 1 km. Based on the good agreement between simulation and observation, we use artificial (passive) tracers, which represent different air mass origins (e.g. vortex, tropics), to further analyse the CRISTA-NF observations in terms of the composition of air mass origins. These passive tracers clearly illustrate the observation of filamentary structures that include tropical air masses. A characteristic of the Arctic winter 2009/10 was a sudden stratospheric warming in December that led to a split of the polar vortex. The vortex re-established at the end of December. Our passive tracer simulations suggest that large parts of the re-established vortex consisted to about 45% of high- and mid-latitude air.

Soil Thermal and Ecological Impacts of Rain on Snow Events in the Circumpolar Arctic

Abstract Rain on snow (ROS) events are rare in most parts of the circumpolar Arctic, but have been shown to have great impact on soil surface temperatures and serve as triggers for avalanches in the midlatitudes, and they have been implicated in catastrophic die-offs of ungulates. The study of ROS is inherently challenging due to the difficulty of both measuring rain and snow in the Arctic and representing ROS events in numerical weather predictions and climate models. In this paper these challenges are addressed, and the occurrence of these events is characterized across the Arctic. Incidents of ROS in Canadian meteorological station data and in the 40-yr ECMWF Re-Analysis (ERA-40) are compared to evaluate the suitability of these datasets for characterizing ROS. The ERA-40 adequately represents the large-scale synoptic fields of ROS, but too often has a tendency toward drizzle. Using the ERA-40, a climatology of ROS events is created for thresholds that impact ungulate populations and permafrost. It is found that ROS events with the potential to harm ungulate mammals are widespread, but the large events required to impact permafrost are limited to the coastal margins of Beringia and the island of Svalbard. The synoptic conditions that led to ROS events on Banks Island in October of 2003, which killed an estimated 20 000 musk oxen, and on Svalbard, which led to significant permafrost warming in December of 1995, are examined. Compositing analyses are used to show the prevailing synoptic conditions that lead to ROS in four disparate parts of the Arctic. Analysis of ROS in the daily output of a fully coupled GCM under a future climate change scenario finds an increase in the frequency and areal extent of these events for many parts of the Arctic over the next 50 yr and that expanded regions of permafrost become vulnerable to ROS.

Predictability of Stratospheric Sudden Warmings as Inferred from Ensemble Forecast Data: Intercomparison of 2001/02 and 2003/04 Winters

The predictability of a minor warming and the subsequent major warming in the winter of 2003/04 is examined in comparison with that of the major warming without preceding minor warmings in December 2001 by the use of operational ensemble 1-month forecast data produced by the Japan Meteorological Agency. In the case of the major warming in December 2001 caused by amplified zonal wavenumber 1 planetary waves, the predictable period based on zonal mean temperatures in the polar stratosphere is estimated to be at least 16 days, while the warmings in the winter of 2003/04 are predictable at most 9 days in advance. Such relatively reduced predictability for the latter warmings is considered due to the rather complicated time evolution of the warming episodes with a significant contribution of smallerscale planetary waves during the period prior to the warmings.

The early major warming in December 2001 – exceptional?

The early major warming in December 2001 is described and compared to the two other December major warmings in 1998 and 1987, showing a strong tropospheric‐stratospheric coupling in all three cases. We argue that the occurrence of free westward propagating Rossby waves interacting with a forced quasi‐stationary wave number 1 led to these three early events. The possible excitation of these waves is discussed with respect to the tropospheric circulation, which showed strong blockings over the northern Atlantic prior to the early major warmings.

Influence of planetary wave transport on Arctic ozone as observed by Polar Ozone and Aerosol Measurement (POAM) III

Interannual differences in Arctic ozone are investigated using data from the Polar Ozone and Aerosol Measurement (POAM) III instrument obtained between May 1998 and April 2001. These three winters were unusually warm or cold relative to the 1979–2001 mean, resulting in years with either a warm, disturbed vortex or a cold, quiet vortex. Contours of probability distribution functions (PDFs) of the POAM data are used to identify seasonal and interannual variations in the transport processes controlling ozone. A major warming in December, 1998, displaced the middle stratospheric vortex from the pole for nearly a month, dissipating it. The vortex reformed in January, 1999, filled with high O3 air from lower latitudes, which then cooled and descended. By the end of winter 1999, ozone at 500 K in the vortex was 0.5–1.0 ppm higher than in the subsequent cold winter. The winter of 2000–2001 had frequent wave disturbances, beginning with a fairly large event in November. However, at the end of this event, the high potential vorticity (PV) core of the vortex was intact, and by February, O3 in the vortex looked the same as in 2000. Transport in these winters is inferred from the PDFs and supported by potential vorticity analyses. This study demonstrates that variability in the O3‐PV relationship can be caused by transport, independent of loss by polar stratospheric clouds (PSCs). Ozone in the vortex in a very disturbed winter can be unusually high due to transport and will not represent O3 levels expected in the absence of PSCs in other years.

Polar OH-airglow temperature variations in the 87/88 winter

Measurements of OH-airglow spectra from Nordlysstasjonen in Adventdalen, Svalbard (15°E, 78°N) from the period 1980–2000 have been done. The temperature at 87 km height was iterated by fitting synthetic spectra to the measured spectra using the vibrational band (6-2). As a first result of the analysis of the time series mesospheric coolings, strong diurnal and semidiurnal tides and a planetary wave have been found in the temperature in the winter of 1987/1988. At the time of the extraordinary early stratospheric warming in December a cooling of 30 K was observed. The strength of the diurnal and semidiurnal tides were 30 K and 15 K respectively. The observation of the planetary wave confirms various models that have shown that mesospheric planetary waves can be generated indirectly by planetary waves in the stratosphere, due to an uneven distribution of the propagation of orographic planetary waves into the mesosphere.

LIMS (Limb Infrared Monitor of the Stratosphere) observation of traveling planetary waves and potential vorticity advection in the stratosphere and mesosphere

Eastward and westward traveling waves were observed by the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) during the northern winter 1978–1979. Eastward waves were prevalent in early winter and were involved in a minor Canadian warming in December 1978. A large westward traveling wave, as described by previous authors, was observed in January 1979 during a series of minor warmings. By comparing these two events, it is shown that in both cases the superposition of traveling and quasi‐stationary waves led to constructive interference that was responsible for the warmings. However, there was significant asymmetry between eastward and westward traveling components. Eastward disturbances were confined mostly within the polar vortex, whereas quasi‐stationary and westward traveling components propagated to the vortex periphery and beyond, into the tropics and mid‐latitude mesosphere. This behavior is consistent with Rossby wave propagation and indicates that the location and magnitude of planetary wave breaking is sensitive to the frequency spectrum entering the middle atmosphere. However, this asymmetry is also a signature of the nonlinear critical layer as it projects onto the frequency spectrum. Both interpretations are shown to be valid during wave events observed by LIMS. A local Eulerian analysis of potential vorticity (PV) transport indicates that adiabatic, geostrophic advection by the resolvable scales of motion explains qualitatively (but not quantitatively) the observed potential vorticity tendencies in the LIMS northern hemisphere winter. In particular, calculated advection explains the eastward rotation of the main vortex, intrusion of low PV air into the polar cap, and formation of high PV filaments at the vortex periphery.

Winds and Wave Motions to 110 km at Mid-Latitudes. III. Response of Mesospheric and Thermospheric Winds to Major Stratospheric Warmings

Abstract The behavior of winds at 52°N, 107°W (Saskatoon, Canada) at altitudes to ∼110 km during major stratospheric warmings of 1969–70,1970–-71 and 1972–73 winters and a minor warming in December 1972, is studied. The zonal component of flow above the stratosphere is found to be affected to varying altitudes; in January 1970 the normal eastward flow was reversed to westward at all altitudes from the surface to ∼110 km. The pattern of winds is reasonably consistent with current suggestions that at middle and high latitudes the mesosphere cools as the stratosphere warms, and that the mesosphere warms subsequent to its cooling. Examples of mesospheric wind perturbations either as precursors of stratospheric warmings or independent of warmings, are also given.

On the interaction between the stratosphere and troposphere during the warming of December 1967‐january 1968

AbstractCalculations of the transfer of kinetic energy from the troposphere to the stratosphere by means of the pressure‐interaction term are carried out for the mid‐winter stratospheric warming of 1967‐1968. This term is computed in the wave number domain for the 100 mb level by means of the Eliassen and Palm (1960) approximation. There appears to be a distinct correlation between the stratospheric kinetic energy per wave number at the 10 mb level and the energy transfer by that wave number at the 100‐mb level. A comparison of the magnitude of the energy flux for 1963 versus that for this later warming suggests that this term is of the same order as the remaining terms in the kinetic energy equation calculated by Perry (1967). Results obtained using this approximation appear to give good agreement with those obtained by direct calculation of the vertical velocity field.