Stratospheric Research Articles

Ultraviolet B radiation affects growth, physiology and fiber quality of cotton

The effects of artificial biologically effective UV-B radiation on a range of growth and physiological parameters in two cotton (Gossypium hirsutum L.) cultivars (Romanos and Allegria) were recorded. Three levels of biologically effective UV-B were used: (1) zero (2) ambient and (3) elevated (determined as that associated with a notional 15% depletion of stratospheric ozone). Plants were grown under artificial light in growth chambers and subjected to the biologically effective UV-B radiation treatments. Compared to the zero level, the ambient and elevated biologically effective UV-B radiation significantly reduced plant height, leaf chlorophyll content, net photosynthetic rate, stomatal conductance, bract length, petal length, anthers number, pollen germination, seed cotton weight, fibre strength, fibre elongation, fibre micronaire, fibre maturity index, fibre spinning consistency index, mean fibre length, fibre yellowness and fibre uniformity index. Both the ambient and the elevated UV-B radiation also significantly increased stomatal density, short fibre index and fibre reflectance. Key words: UV-B radiation, cotton, photosynthesis, stomatal density, flower characteristics, pollen germination, seed cotton weight, fibre quality.

The role of wave–wave interactions in sudden stratospheric warming formation

Abstract. The effects of wave–wave interactions on sudden stratospheric warming formation are investigated using an idealized atmospheric general circulation model, in which tropospheric heating perturbations of zonal wave numbers 1 and 2 are used to produce planetary-scale wave activity. Zonal wave–wave interactions are removed at different vertical extents of the atmosphere in order to examine the sensitivity of stratospheric circulation to local changes in wave–wave interactions. We show that the effects of wave–wave interactions on sudden warming formation, including sudden warming frequencies, are strongly dependent on the wave number of the tropospheric forcing and the vertical levels where wave–wave interactions are removed. Significant changes in sudden warming frequencies are evident when wave–wave interactions are removed even when the lower-stratospheric wave forcing does not change, highlighting the fact that the upper stratosphere is not a passive recipient of wave forcing from below. We find that while wave–wave interactions are required in the troposphere and lower stratosphere to produce displacements when wave number 2 heating is used, both splits and displacements can be produced without wave–wave interactions in the troposphere and lower stratosphere when the model is forced by wave number 1 heating. We suggest that the relative strengths of wave number 1 and 2 vertical wave flux entering the stratosphere largely determine the split and displacement ratios when wave number 2 forcing is used but not wave number 1.

Experimental Global Forecasts of Atmospheric Parameters Based on Experimental Technology that Takes into Account Ozone Photochemistry (FOROZ Model)

The results of numerical seasonal forecasts of temperature calculated with two interactive global numerical models, the CHARM photochemical model (0–90 km) of the Central Aerological Observatory (CAO) and the seasonal forecast model PLAV of the Hydrometeorological Centre/Institute of Numerical Mathematics of the Russian Academy of Sciences (0–30 km), are presented. The wind and temperature fields above 30 km were linked with the CAO ARM general circulation model. The forecast results are compared with reanalysis data. The calculations show that the new combined model (Forecast with Ozone, FOROZ) is stable under numerical scenarios. The seasonal forecast temperature fields of the PLAV model and the combined FOROZ model with reanalysis data are close in the lower troposphere and differ in the stratosphere. The combined FOROZ model improves the temperature forecast for the upper troposphere and stratosphere.

Barotropic instability of a zonal jet on the sphere: from non-divergence through quasi-geostrophy to shallow water

Two common approximations to the full Shallow Water Equations (SWEs) are non-divergence and quasi-geostrophy, and the degree to which these approximations lead to biases in numerical solutions are explored using the test bed of barotropic instability. Specifically, we examine the linear stability of strong polar and equatorial jets and compare the growth rates obtained from the SWEs along with those obtained from the Non-Divergent barotropic vorticity (ND) equation and the Quasi-Geostrophic (QG) equation. The main result of this paper is that the depth over which a layer is barotropically unstable is a crucial parameter in controlling the growth rate of small amplitude perturbations and this dependence is completely lost in the ND equation and is overly weak in the QG system. Only for depths of 30 km or more are the growth rates predicted by the ND and QG systems a good approximation to those of the SWEs, and such a convergence for deep layers can be explained using theoretical considerations. However, for smaller depths, the growth rates predicted by the SWEs become smaller than those of the ND and QG systems and for depths of between 5 and 10 km they can be smaller by more than . For polar jets, and for depths below 2 km the mean height in geostrophic balance with the strong zonal jet becomes negative and hence the barotropic instability problem is ill-defined. While in the SWEs an equatorial jet becomes stable for layer depths smaller than 3–4 km, in the QG and ND approximations it is unstable for layer depths down to 1 km. These result may have implications for the importance of barotropic instability in Earth's upper stratosphere and perhaps also other planets such as Venus.

Stratospheric temperature anomalies as imprints from the dark Universe

The manifestation of the dark Universe begun with unexpected large scale astronomical observations. Here we are investigating the origin of small scale anomalies, like that of the annually observed temperature anomalies in the stratosphere. Unexpectedly, we observe a planetary relationship of the daily stratospheric temperature distribution. Its spectral shape does not match concurrent solar activity, or solar EUV emission, whose impact on the atmosphere is unequivocal. This behavior points at an additional energy source of exosolar origin. A viable concept behind such observations is based on possible gravitational focusing by the solar system towards the Earth of low speed invisible matter. We denote generic constituents from the dark Universe as invisible matter, in order to distinguish them from ordinary dark matter candidates like axions or WIMPs, which cannot have any noticeable impact on the stratosphere. The observed peaking planetary relations exclude on their own any conventional explanation. Only a somehow strongly interacting invisible streaming matter with the little screened upper stratosphere (noverhead about 1 gr/cm 2) can be behind the occasionally observed temperature increases. We also estimate an associated energy deposition O(W/m 2), which is variable over the 11 years solar cycle. For the widely assumed picture of a quasi not interacting dark Universe, this new exosolar energy is enormous. Since the atmosphere is uninterruptedly monitored since decades, it can serve also parasitically as a novel low threshold detector for the dark Universe, with built-in spatiotemporal resolution and the solar system acting temporally as signal amplifier. In future, analyzing more observations, for example, from the anomalous ionosphere, or, the transient sudden stratospheric warmings, the nature of the assumed invisible streams could be deciphered.

Does the Arctic Stratospheric Polar Vortex Exhibit Signs of Preconditioning Prior to Sudden Stratospheric Warmings?

Abstract Characteristics of the Arctic stratospheric polar vortex are examined using reanalysis data with dynamic time warping (DTW) and a clustering technique to determine whether the polar vortex exhibits canonical signs of preconditioning prior to sudden stratospheric warmings (SSWs). The DTW and clustering technique is used to locate time series motifs in vortex area, vortex edge-averaged PV gradients, and vortex edge-averaged wind speeds. Composites of the motifs reveal that prior to roughly 75% of SSWs, in the middle to upper stratosphere, PV gradients and wind speeds in the vortex edge region increase, and vortex area decreases. These signs agree with prior studies that discuss potential signals of preconditioning of the vortex. However, similar motifs are also found in a majority of years without SSWs. While such non-SSW motifs are strongly associated with minor warming signals apparent only in the middle and upper stratosphere, only roughly half of these can be associated with later “significant disturbances” (SDs) that do not quite meet the threshold for major SSWs. The median lead time for sharpening vortex edge PV gradients represented in the motifs prior to SSWs and SDs is ~25 days, while the median lead time for the vortex area and edge wind speeds is ~10 days. Overall, canonical signs of preconditioning do appear to exist prior to SSWs, but their existence in years without SSWs implies that preconditioning of the vortex may be an insufficient condition for the occurrence of SSWs.

Stability of halocarbons in air samples stored in stainless- steel canisters

Abstract. Measurements of halogenated trace gases in ambient air frequently rely on canister sampling followed by offline laboratory analysis. This allows for a large number of compounds to be analysed under stable conditions, maximizing measurement precision. However, individual compounds might be affected during the sampling and storage of canister samples. In order to assess halocarbon stability in whole-air samples from the upper troposphere and lowermost stratosphere, we performed stability tests using the high-resolution sampler (HIRES) air sampling unit, which is part of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) instrument package. The HIRES unit holds 88 lightweight stainless-steel cylinders that are pressurized in flight to 4.5 bar using metal bellows pumps. The HIRES unit was first deployed in 2010 but has up to now not been used for regular halocarbon analysis with the exception of chloromethane analysis. The sample collection unit was tested for the sampling and storage effects of 28 halogenated compounds. The focus was on compound stability in the stainless-steel canisters during storage of up to 5 weeks and on the influence of ozone, since flights take place in the upper troposphere and lowermost stratosphere with ozone mixing ratios of up to several hundred parts per billion by volume (ppbv). Most of the investigated (hydro)chlorofluorocarbons and long-lived hydrofluorocarbons were found to be stable over a storage time of up to 5 weeks and were unaltered by ozone being present during pressurization. Some compounds such as dichloromethane, trichloromethane, and tetrachloroethene started to decrease in the canisters after a storage time of more than 2 weeks or exhibited lowered mixing ratios in samples pressurized with ozone present. A few compounds such as tetrachloromethane and tribromomethane were found to be unstable in the HIRES stainless-steel canisters independent of ozone levels. Furthermore, growth was observed during storage for some species, namely for HFC-152a, HFC-23, and Halon 1301.

The equatorial stratospheric semiannual oscillation and time‐mean winds in QBOi models

AbstractThe Quasi‐Biennial Oscillation initiative (QBOi) is a model intercomparison programme that specifically targets simulation of the QBO in current global climate models. Eleven of the models or model versions that participated in a QBOi intercomparison study have upper boundaries in or above the mesosphere and therefore simulate the region where the stratopause semiannual oscillation (SAO) is the dominant mode of variability of zonal winds in the tropical upper stratosphere. Comparisons of the SAO simulations in these models are presented here. These show that the model simulations of the amplitudes and phases of the SAO in zonal‐mean zonal wind near the stratopause agree well with the information derived from available observations. However, most of the models simulate time‐average zonal winds that are more westward than determined from observations, in some cases by several tens of m·s–1. Validation of wave activity in the models is hampered by the limited observations of tropical waves in the upper stratosphere but suggests a deficit of eastward forcing either by large‐scale waves, such as Kelvin waves, or by gravity waves.

ИССЛЕДОВАНИЕ ИЗМЕНЕНИЙ ДИНАМИКИ СТРАТОСФЕРЫ СЕВЕРНОГО ПОЛУШАРИЯ В XXI ВЕКЕ ПО РАСЧЕТАМ КЛИМАТИЧЕСКОЙ МОДЕЛИ ИВМ РАН

Simulations of 5th version of INM RAS (Institute of Numerical Mathematics of the Russian Academy of Science) climate model performed in the framework of CMIP6 project for the future climate under ssp2–4.5 (moderate) and ssp5–8.5 (business as usual or hard) scenarios of green house gases (GHG) increase are employed to analyze temperature, zonal mean wind, stratospheric polar vortex, planetary wave activity, meridional circulation, sudden stratospheric warming (SSW) events, and stratospheric circulation spring break-up date changes during boreal winters from 2015 to 2100. Comparison of averages over two periods of 2080–2100 and 2015–2035 revealed that temperature will decrease from 1° in the lower stratosphere to 4° in the upper stratosphere under moderate scenario and up to 11° under hard scenario. Cooling of stratosphere will be accompanied by strengthening of zonal circulation and planetary wave activity propagation in the middle – upper stratosphere that in turn leads to increase (stronger under hard scenario) of planetary wave with zonal wave number 1 amplitude (wavenumber 1). 13 major sudden stratospheric warming events and 16 very cold stratospheric winter seasons were revealed under hard scenario. Under both scenarios early spring break-up dates will be accompanied by stronger wavenumber 1 in comparison with winter seasons with later spring break-up dates. Strengthening of zonal mean meridional circulation is expected in the late XXI century

Inertial gravity waves observed by a Doppler wind LiDAR and their possible sources

In this paper, we use wind observations by a Doppler wind LiDAR near Delingha (37.4°N, 97.4°E), Qinghai, Northwestern China to study the characteristics of inertial gravity waves in the stratosphere. We focus on 10–12 December 2013, a particularly interesting case study. Most of the time, the inertial gravity waves extracted from the LiDAR measurements were stationary with vertical wavelengths of about 9–11 km and horizontal wavelengths of about 800–1000 km. However, for parts of the observational period in this case study, a hodograph analysis indicates that different inertial gravity wave propagation features were present at lower and upper altitudes. In the middle and upper stratosphere (~30–50 km), the waves propagated downward, especially during a period of stronger winds, and to the northwest–southeast. In the lower stratosphere and upper troposphere (~10–20 km), however, waves with upward propagation and northeast–southwest orientation were dominant. By taking into account reanalysis data and satellite observations, we have confirmed the presence of different wave patterns in the lower and upper stratosphere during this part of the observational period. The combined data sets suggest that the different wave patterns at lower and upper height levels are likely to have been associated with the presence of lower and upper stratospheric jet streams.

Reponses of middle atmospheric circulation to the 2009 major sudden stratospheric warming

In this research, the roles of gravity waves and planetary waves in the change to middle atmospheric residual circulation during a sudden stratospheric warming period are differentiated and depicted separately by adopting the downward control principle. Our analysis shows clear anomalous poleward residual circulation patterns from the equator to high latitudes in the lower winter stratosphere. At the same time, upward mean flows are identified at high latitudes of the winter upper stratosphere and mesosphere, which turn equatorward in the mesosphere and reach as far as the tropical region, and consequently the extratropical region in the summer hemisphere. The downward control principle shows that anomalous mesospheric residual circulation patterns, including interhemispheric coupling, are solely caused by the change in gravity wave forcing resulting from the reversal of the winter stratospheric zonal wind. Nevertheless, both planetary waves and gravity waves are important to variations in the winter stratospheric circulation, but with opposite effects.

Solar wind signal in the wintertime North Atlantic oscillation and Northern Hemispheric circulation

AbstractThe impact of the solar wind on sea level pressure (SLP), sea surface temperature (SST), zonal mean zonal wind (U) and air temperature (T) was examined using multiple linear regression analysis. Our analysis of the December–January–February (DJF) mean fields indicates that significant links between the solar wind speed (SWS) and the North Atlantic oscillation (NAO), SST tripolar structure and polar stratospheric temperature. The monthly reanalysis data (November to March) show that high SWS is associated with a poleward‐ and downward‐ propagating solar wind signal from December to February. The response of the Eliassen‐Palmer (EP) flux shows that more planetary wave activity is refracted equatorward in the upper stratosphere under higher SWS conditions, corresponding to an enhanced EP flux convergence in early winter. Enhanced EP flux divergence occurs in the stratosphere starting in January and propagates poleward and downward from January to February. For the coupling mechanism between the stratosphere and troposphere, in addition to chemical‐dynamical processes, cloud microphysical processes associated with the global electric circuit (GEC) might play a role in the downward propagation of the solar wind signal and the modulation of the NAO.

Interannual Variation of Upper Stratospheric Ozone in the Northern Midlatitudes in Early Winter Caused by Planetary Waves

AbstractOzone mixing ratios in the upper stratosphere, observed with a millimeter‐wave radiometer at Rikubetsu (43.46°N, 143.77°E), Japan, from November 1999 to February 2017 showed both interannual and seasonal variation, which was characterized by a winter maximum and a summer minimum. During the study period, the summer minima were nearly constant whereas the winter maxima varied interannually and also displayed short‐term variability. The observed ozone mixing ratios at 1 hPa were anticorrelated with temperature at 1 hPa from MERRA‐2 data. The slope of the relationship between the logarithm of ozone concentration and the reciprocal of temperature differed between winter data and both summer and annual data. Therefore, we inferred that both chemistry and dynamics affect short‐term variation of ozone mixing ratios in winter. We then examined the contribution of the polar vortex to interannual variations in ozone and temperature at 1 hPa. When the polar vortex was strong, wave number‐1 planetary waves at high latitude propagated toward the midlatitudes instead of vertically. The vertical component of the wave number‐1 Eliassen‐Palm flux along 43°N at 1 hPa was strongly correlated with zonal mean zonal wind along 60°N at 50 hPa. When the zonal mean westerly wind was strong in December, upper stratospheric (~1 hPa) temperatures over Rikubetsu and over a point on the opposite side of the globe (by longitude) were significantly lower and higher, respectively, than the climatological temperature. Thus, planetary wave propagation related to zonal mean westerly wind strength induced early winter interannual variation in upper stratospheric ozone in the midlatitudes.

Seasonal Evolution of the Quasi‐biennial Oscillation Impact on the Northern Hemisphere Polar Vortex in Winter

AbstractUsing potential vorticity to define Northern Hemisphere (NH) stratospheric polar vortex strength and position, the influence of the QBO on the polar vortex in winter is analyzed. The results show that the weakened/enhanced NH polar vortex in the lower stratosphere during easterly/westerly QBO (E/WQBO) phases is more noticeable in January and February than in November and December. Furthermore, the NH polar vortex shows a shift toward the Eurasian continent and away from North America in winter during EQBO phases compared with that during WQBO phases, with a greater shift in January and February than in November and December. The weaker QBO impact on the zonal mean zonal wind and temperature in February found in previous studies may be related to the cancelling effects of opposite‐signed anomalies over Eurasia and North America induced by the polar vortex shift associated with the QBO. During EQBO phases the upper stratospheric easterly anomalies in early winter increase the frequency of negative refractive index in the middle and high latitudes in late winter. Less planetary wave 1 propagates upward into the upper stratosphere and more wave 1 accumulates in the lower stratosphere, leading to the weakening and shift of the polar vortex in late winter. In addition, the poleward displacement of the subtropical jet during EQBO phases causes more poleward propagation of synoptic‐scale waves in the lower stratosphere, and thus more Rossby wave breaking events over Eurasia in late winter than during WQBO phases, further weakening and shifting the polar vortex in EQBO phases.

The Possible Responses of Polar Ozone to Solar Proton Events in March 2012 by FengYun‐3 Satellite Observations

AbstractIn this work, we use observations by the Solar Backscatter Ultraviolet Sounder and Space Environment Monitor on FengYun‐3 to analyze the polar ozone depletion during the solar proton events (SPEs), which occurred in early March 2012. The ozone distributions changed evidently with the increasing energetic proton flux (the particle energy is over 100 MeV) at the approximate altitude of 30 km. From the ozone profile relative changes, the short‐term impacts of SPEs can be distinguished from the long‐term effects of ozone season variations after the SPEs take place and cause about 4–17% of the short‐term polar ozone decreases at the different levels in the upper stratosphere of both hemispheres. In the upper stratosphere, the SPE‐related polar ozone depletion is more significant and continuous in the Northern Hemisphere but shows the short‐term effects in the Southern Hemisphere during the March SPEs. The ozone depletion responses to the first SPE on 7 March are more pronounced in this altitude region than the second one on 13 March in both hemispheres due to the “harder” particle energy spectrum.

Is the recovery of stratospheric O<sub>3</sub> speeding up in the Southern Hemisphere? An evaluation from the first IASI decadal record (2008–2017)

Abstract. In this paper, we present the global fingerprint of recent changes in middle–upper stratosphere (MUSt; <25 hPa) ozone (O3) in comparison with lower stratosphere (LSt; 150–25 hPa) O3 derived from the first 10 years of the IASI/Metop-A satellite measurements (January 2008–December 2017). The IASI instrument provides vertically resolved O3 profiles with very high spatial and temporal (twice daily) samplings, allowing O3 changes to be monitored in these two regions of the stratosphere. By applying multivariate regression models with adapted geophysical proxies on daily mean O3 time series, we discriminate anthropogenic trends from various modes of natural variability, such as the El Niño–Southern Oscillation (ENSO). The representativeness of the O3 response to its natural drivers is first examined. One important finding relies on a pronounced contrast between a positive LSt O3 response to ENSO in the extratropics and a negative one in the tropics, with a delay of 3 months, which supports a stratospheric pathway for the ENSO influence on lower stratospheric and tropospheric O3. In terms of trends, we find an unequivocal O3 recovery from the available period of measurements in winter–spring at middle to high latitudes for the two stratospheric layers sounded by IASI (>∼35∘ N–S in the MUSt and >∼45∘ S in the LSt) as well as in the total columns at southern latitudes (>∼45∘ S) where the increase reaches its maximum. These results confirm the effectiveness of the Montreal Protocol and its amendments and represent the first detection of a significant recovery of O3 concurrently in the lower, in the middle–upper stratosphere and in the total column from one single satellite dataset. A significant decline in O3 at northern mid-latitudes in the LSt is also detected, especially in winter–spring of the Northern Hemisphere. Given counteracting trends in the LSt and MUSt at these latitudes, the decline is not categorical in total O3. When freezing the regression coefficients determined for each natural driver over the whole IASI period but adjusting a trend, we calculate a significant speeding up in the O3 response to the decline of O3-depleting substances (ODSs) in the total column, in the LSt and, to a lesser extent, in the MUSt, at high southern latitudes over the year. Results also show a small significant acceleration of the O3 decline at northern mid-latitudes in the LSt and in the total column over the last few years. That, specifically, needs urgent investigation to identify its exact origin and apprehend its impact on climate change. Additional years of IASI measurements would, however, be required to confirm the O3 change rates observed in the stratospheric layers over the last few years.

Possible implications of enhanced chlorofluorocarbon-11 concentrations on ozone

Abstract. This numerical model study is motivated by the observed global deviation from assumed emissions of chlorofluorocarbon-11 (CFC-11, CFCl3) in recent years. Montzka et al. (2018) discussed a strong deviation of the assumed emissions of CFC-11 over the past 15 years, which indicates a violation of the Montreal Protocol for the protection of the ozone layer. An investigation is performed which is based on chemistry–climate model (CCM) simulations that analyze the consequences of an enhanced CFC-11 surface mixing ratio. In comparison to a reference simulation (REF-C2), where a decrease of the CFC-11 surface mixing ratio of about 50 % is assumed from the early 2000s to the middle of the century (i.e., a mixing ratio in full compliance with the Montreal Protocol agreement), two sensitivity simulations are carried out. In the first simulation the CFC-11 surface mixing ratio is kept constant after the year 2002 until 2050 (SEN-C2-fCFC11_2050); this allows a qualitative estimate of possible consequences of a high-level stable CFC-11 surface mixing ratio on the ozone layer. In the second sensitivity simulation, which is branched off from the first sensitivity simulation, it is assumed that the Montreal Protocol is fully implemented again starting in the year 2020, which leads to a delayed decrease of CFC-11 in this simulation (SEN-C2-fCFC11_2020) compared with the reference simulation; this enables a rough and most likely upper-limit assessment of how much the unexpected CFC-11 emissions to date have already affected ozone. In all three simulations, the climate evolves under the same greenhouse gas scenario (i.e., RCP6.0) and all other ozone-depleting substances decline (according to this scenario). Differences between the reference (REF-C2) and the two sensitivity simulations (SEN-C2-fCFC11_2050 and SEN-C2-fCFC11_2020) are discussed. In the SEN-C2-fCFC11_2050 simulation, the total column ozone (TCO) in the 2040s (i.e., the years 2041–2050) is particularly affected in both polar regions in winter and spring. Maximum discrepancies in the TCO values are identified with reduced ozone values of up to around 30 Dobson units in the Southern Hemisphere (SH) polar region during SH spring (in the order of 15 %). An analysis of the respective partial column ozone (PCO) for the stratosphere indicates that the strongest ozone changes are calculated for the polar lower stratosphere, where they are mainly driven by the enhanced stratospheric chlorine content and associated heterogeneous chemical processes. Furthermore, it was found that the calculated ozone changes, especially in the upper stratosphere, are surprisingly small. For the first time in such a scenario, we perform a complete ozone budget analysis regarding the production and loss cycles. In the upper stratosphere, the budget analysis shows that the additional ozone depletion due to the catalysis by reactive chlorine is partly compensated for by other processes related to enhanced ozone production or reduced ozone loss, for instance from nitrous oxide (NOx). Based on the analysis of the SEN-C2-fCFC11_2020 simulation, it was found that no major ozone changes can be expected after the year 2050, and that these changes are related to the enhanced CFC-11 emissions in recent years.

Influences of atmospheric ventilation on the composition of the upper troposphere and lower stratosphere during the two primary modes of the South Asia high

There are two key modes of the South Asia high (SAH) during the boreal summer: the Iranian Plateau (IP) and Tibetan Plateau (TP) modes. The anomalies of chemical constituents in the upper troposphere and lower stratosphere (UTLS) region within the SAH area largely depend on this bimodality. To better understand the underlying mechanisms of this dependence, the ensemble of 30-day backward trajectories, initialized in the UTLS region within the SAH, was simulated by a Lagrangian model FLEXPART. The comparative diagnostic was performed from the perspective of atmospheric ventilation. The results show that vertical transport from the lower troposphere to the UTLS during the TP mode was very efficient, resulting in tropospheric air mass transported into the UTLS within a shorter timescale than during the IP mode. Furthermore, the effect of SAH isolation during the TP mode was stronger than during the IP mode. This stronger trapping is likely to force the tropospheric air mass to reside in the SAH area for a longer period of time. In addition, compared to the IP mode, near-surface air mass sources during the TP mode overlapped more with areas of severe air pollution (CO emissions). The above three factors associated with the processes of atmospheric ventilation, i.e., the efficiency of vertical transport, the strength of the SAH isolation, and the boundary layer sources, provide potential explanations as to why the anomalies of atmospheric constituents in the UTLS are different between the TP and the IP mode.

Error growth in the Mesosphere and Lower Thermosphere Based on Hindcast Experiments in a Whole Atmosphere Model

AbstractThe capability to forecast conditions in the mesosphere and lower thermosphere is investigated based on 30‐day hindcast experiments that were initialized bimonthly during 2009 and 2010. The hindcasts were performed using the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCMX) with data assimilation provided by the Data Assimilation Research Testbed (DART) ensemble Kalman filter. Analysis of the WACCMX+DART hindcasts reveals several important features that are relevant to forecasting the middle atmosphere. The results show a clear dependence on spatial scale, with the slowest error growth occurring in the zonal mean and the fastest error growth occurring for small‐scale waves. The error growth rate is also found to be significantly greater in the upper mesosphere and lower thermosphere compared to in the upper stratosphere to lower mesosphere, suggesting that the forecast skill decreases with increasing altitude. The results demonstrate that the errors in the lower thermosphere reach saturation, on average, in less than 5 days, at least with the current version of WACCMX+DART. A seasonal dependency to the error growth is found at high latitudes in the Northern and Southern Hemispheres but not in the tropics or global average. We additionally investigate the error growth rates for migrating and nonmigrating atmospheric tides and find that the errors saturate after ∼5 days for tides in the lower thermosphere. The results provide an initial assessment of the error growth rates in the mesosphere and lower thermosphere and are relevant for understanding how whole atmosphere models can potentially improve space weather forecasting.

A Two-Season Impact Study of Radiative Forced Tropospheric Response to Stratospheric Initial Conditions Inferred From Satellite Radiance Assimilation

This study investigated the impacts of stratospheric temperatures and their variations on tropospheric short-term weather forecasting using the Advanced Research Weather Research and Forecasting (WRF-ARW) system with real satellite data assimilation. Satellite-borne microwave stratospheric temperature measurements up to 1 mb, from the Advanced Microwave Sounding Unit-A (AMSU-A), the Advanced Technology Microwave Sounder (ATMS), and the Special Sensor microwave Imager/Sounder (SSMI/S), were assimilated into the WRF model over the continental U.S. during winter and summer 2015 using the community Gridpoint Statistical Interpolation (GSI) system. Adjusted stratospheric temperature related to upper stratospheric ozone absorption of short-wave (SW) radiation further lead to vibration in downward SW radiation in winter predictions and overall reduced with a maximum of 5.5% reduction of downward SW radiation in summer predictions. Stratospheric signals in winter need 48- to 72-h to propagate to the lower troposphere while near-instant tropospheric response to the stratospheric initial conditions are observed in summer predictions. A schematic plot illustrated the physical processes of the coupled stratosphere and troposphere related to radiative processes. Our results suggest that the inclusion of the entire stratosphere and better representation of the upper stratosphere are important in regional NWP systems in short-term forecasts.