NRLMSIS® 2.0 is an empirical atmospheric model that extends from the ground to the exobase and describes the average observed behavior of temperature, eight species densities, and mass density via a ...parametric analytic formulation. The model inputs are location, day of year, time of day, solar activity, and geomagnetic activity. NRLMSIS 2.0 is a major, reformulated upgrade of the previous version, NRLMSISE‐00. The model now couples thermospheric species densities to the entire column, via an effective mass profile that transitions each species from the fully mixed region below ~70 km altitude to the diffusively separated region above ~200 km. Other changes include the extension of atomic oxygen down to 50 km and the use of geopotential height as the internal vertical coordinate. We assimilated extensive new lower and middle atmosphere temperature, O, and H data, along with global average thermospheric mass density derived from satellite orbits, and we validated the model against independent samples of these data. In the mesosphere and below, residual biases and standard deviations are considerably lower than NRLMSISE‐00. The new model is warmer in the upper troposphere and cooler in the stratosphere and mesosphere. In the thermosphere, N2 and O densities are lower in NRLMSIS 2.0; otherwise, the NRLMSISE‐00 thermosphere is largely retained. Future advances in thermospheric specification will likely require new in situ mass spectrometer measurements, new techniques for species density measurement between 100 and 200 km, and the reconciliation of systematic biases among thermospheric temperature and composition data sets, including biases attributable to long‐term changes.
Key Points
A major, reformulated upgrade to NRLMSISE‐00 is presented using extensive new data sets from the ground to ~100 km altitude
Vertical structure of the atmosphere is now self‐consistently coupled; O density now extends down to 50 km
New model is warmer in upper troposphere, cooler in stratosphere and mesosphere; thermospheric N2 and O densities are lower
The magnetosphere‐ionosphere‐thermosphere system is externally driven by the energy input from the solar wind. A part of the solar wind energy deposited in the magnetosphere during geomagnetically ...active periods dissipates into the thermosphere. Previous studies have reported temperature perturbations in the lower thermosphere during geomagnetic storms. The present study aims to assess the climatological spatial pattern of the lower thermospheric response to geomagnetic activity at high latitudes based on 21 years of temperature measurements by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite and their comparison with the recently developed half‐hourly geomagnetic activity index Hp30. The temperature response to geomagnetic activity, evaluated at different seasons and altitudes, is better organized in magnetic coordinates than in geographic coordinates. At 110 km, the temperature increases with Hp30 at all magnetic local times, but with a prominent dusk‐dawn asymmetry in the magnitude. That is, the temperature variation per unit Hp30 is larger in the dusk sector than in the dawn sector. At 106 km, the response in the dawn sector is further reduced or even negative. These results provide observational evidence to support earlier theoretical predictions; according to which, both storm‐induced vertical wind and Joule heating contribute to the temperature increase in the dusk sector, while in the dawn sector, the vertical wind acts to cool the air and thus counteracts Joule heating.
Key Points
High‐latitude lower thermospheric temperature response to geomagnetic activity depends on magnetic local time and magnetic latitude
Above 100 km, strong and weak (or even negative) responses occur in the dusk and dawn sectors, respectively
The results agree with earlier theoretical predictions, highlighting the importance of storm‐induced vertical wind and Joule heating
In this work absolute values of gravity wave (GW) momentum flux are derived from global temperature measurements by the satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and ...Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Momentum fluxes in the stratosphere are derived for both instruments and for SABER in the whole mesosphere. The large‐scale atmospheric background state is removed by a two‐dimensional Fourier decomposition in longitude and time, covering even planetary‐scale waves with periods as short as 1–2 days. Therefore, it is possible to provide global distributions of GW momentum flux from observations for the first time in the mesosphere. Seasonal as well as longer‐term variations of the global momentum flux distribution are discussed. GWs likely contribute significantly to the equatorward tilt of the polar night jet and to the poleward tilt of the summertime mesospheric jet. Our results suggest that GWs can undergo large latitudinal shifts while propagating upward. In particular, GWs generated by deep convection in the subtropical monsoon regions probably contribute significantly to the mesospheric summertime wind reversal at mid‐ and high latitudes. Variations in the GW longitudinal distribution caused by those convectively generated GWs are still observed in the mesosphere and could be important for the generation of the quasi two‐day wave. Indications for quasi‐biennial oscillation (QBO) induced variations of GW momentum flux are found in the subtropics. Also variations at time scales of about one 11‐year solar cycle are observed and might indicate a negative correlation between solar flux and GW momentum flux.
Key Points
Gravity wave momentum flux global distributions in both strato‐ and mesosphere
Interaction of gravity waves with zonal wind jets studied
Discussion of variations on different timescales: seasonal, QBO, solar cycle
Measurements from 2002 to 2011 by three independent satellite instruments, namely MIPAS, SABER, and SMR on board the ENVISAT, TIMED, and Odin satellites are used to investigate the intra-seasonal ...variability of stratospheric and mesospheric O3 volume mixing ratio (vmr) inside the Antarctic polar vortex due to solar and geomagnetic activity. In this study, we individually analysed the relative O3 vmr variations between maximum and minimum conditions of a number of solar and geomagnetic indices (F10.7 cm solar radio flux, Ap index, ≥ 2 MeV electron flux). The indices are 26-day averages centred at 1 April, 1 May, and 1 June while O3 is based on 26-day running means from 1 April to 1 November at altitudes from 20 to 70 km. During solar quiet time from 2005 to 2010, the composite of all three instruments reveals an apparent negative O3 signal associated to the geomagnetic activity (Ap index) around 1 April, on average reaching amplitudes between −5 and −10% of the respective O3 background. The O3 response exceeds the significance level of 95% and propagates downwards throughout the polar winter from the stratopause down to ~ 25 km. These observed results are in good qualitative agreement with the O3 vmr pattern simulated with a three-dimensional chemistry-transport model, which includes particle impact ionisation.
The seasonal and interannual variability of migrating (Sun‐synchronous) and nonmigrating solar atmospheric tides at altitudes between 100 and 116 km are investigated using temperature measurements ...made with the SABER instrument on the TIMED spacecraft during 2002–2006. Quasi‐biennial variations of order ±10–15% in migrating diurnal and semidiurnal tidal amplitudes are found, presumably due to modulation by the quasi‐biennial oscillation (QBO) as the tides propagate from their troposphere and stratospheric sources to the lower thermosphere. A number of nonmigrating tidal components are found that have the potential to produce significant longitudinal variability of the total tidal fields. The most prominent of these, i.e., those that appear at amplitudes of order 5–10 K in a 5‐year mean climatology, include the zonally symmetric (s = 0) diurnal tide (D0); the eastward propagating diurnal and semidiurnal tides with zonal wave numbers s = −2 (DE2 and SE2) and s = −3 (DE3 and SE3); and the following westward propagating waves: diurnal s = 2 (DW2); semidiurnal s = 1 (SW1), s = 3 (SW3), and s = 4 (SW4); and terdiurnal s = 5 (TW5). These waves can be plausibly accounted for by nonlinear interaction between migrating tidal components and stationary planetary waves with s = 1 or s = 2 or by longitudinal variations of tropospheric thermal forcing. Additional waves that occur during some years or undergo phase cancellation within construction of a 5‐year climatology include DW5, SE1, SE4, SW6, TE1, TW1, and TW7. It is anticipated that the winds that accompany all of these waves in the 100–170 km region will impose longitudinal variability in the electric fields produced through the ionospheric dynamo mechanism, thereby modulating vertical motion of the equatorial ionosphere and the concomitant plasma densities. In addition to the wave‐4 modulation of the equatorial ionosphere that has recently been discovered and replicated in modeling studies, the waves revealed here will generate wave‐1 (SW1, SW3, D0, DW2), wave‐2 (SW4, TW1), wave‐3 (DE2, SE1), wave‐4 (DE3, SE2, DW5, SW6, TE1, TW7), wave‐5 (SE3), and wave‐6 (SE4) components of this ionospheric variability, depending on year and time of year. However, the absolute and relative efficiencies with which these waves produce electric fields remains to be determined.
Gravity waves (GWs) play an important role in the dynamics and energetics of the mesosphere. Geomagnetic activity is a known source of GWs in the upper atmosphere. However, how deep the effects of ...geomagnetic activity induced GWs penetrate into the mesosphere remains an open question. We use temperature measurements from the SABER/TIMED instrument between 2002 and 2018 to study the variations of mesospheric GW activity following intense geomagnetic disturbances identified by AE and Dst indices. By considering several case studies, we show for the first time that the GWs forced by geomagnetic activity can propagate down to about 80 km in the high latitude mesosphere. Only regions above 55° latitudes show a clear response. The fraction of cases in which there is an unambiguous enhancement in GW activity following the onset of geomagnetic disturbance is smaller during summer than other seasons. Only about half of the events show an unambiguous increase in GW activity during non‐summer periods and about one quarter of the events in summer show an enhancement in GWs. In addition, we also find that the high latitude mesopause is often seen to descend in altitude following onset of geomagnetic activity in the non‐summer high latitude region.
Plain Language Summary
Gravity waves (GWs) exist throughout the atmosphere and are crucial in the dynamics of the middle and upper atmosphere. A variety of processes are known to excite GWs at different altitudes. Above 100 km, space weather induced geomagnetic activity is an important source for the GWs. However, how deep such waves penetrate into the mesosphere, and in what latitude regions their effect is important remains unknown. In this work, we use SABER/TIMED satellite measurements of temperature between 2002 and 2018 to investigate this question. For the first time, we find that the geomagnetic activity forces mesospheric GWs only in the high latitude regions, where enhanced energy deposition occurs along magnetic field lines. Further, these GWs occur only above 80 km, and no unambiguous signature is seen at lower heights. Though damping is expected due to the increasing atmospheric density, this work identifies the altitude and latitude extent for such GWs forced by geomagnetic activity in the mesosphere. Further, there is a significant seasonality in the response such that summer hemisphere shows weakest GW generation due to geomagnetic activity. The mesopause height is also observed to descend sometimes during intense geomagnetic disturbances occurring in non‐summer periods.
Key Points
Geomagnetically forced gravity waves penetrate down to ∼80 km only in the high latitude regions as revealed by Sounding of the Atmosphere using Broadband Emission Radiometry temperature data
Summer high latitude mesosphere is less responsive for gravity wave generation due to geomagnetic activity
Significant variability in the gravity wave response is noticed even between severe geomagnetic disturbances occurring in the same season
This paper characterizes the impacts of sudden stratospheric warmings (SSWs) and mesospheric coolings (MCs) on the light species distribution (i.e., helium He, and atomic hydrogen H) of the ...thermosphere using a combined data‐modeling approach. Performing a set of numerical experiments with a general circulation model whose middle atmospheric dynamical and thermodynamical fields were constrained using a numerical weather prediction system, we simulate the effects of SSWs and MCs on light chemical species, and via comparisons with two data sets taken from the mesosphere and thermosphere, we quantify the associated variability in light species abundances and mass density. Large depletions in the observed and modeled polar H abundance in the mesosphere and lower thermosphere (MLT) occur with MC onset, as opposed to SSW onset. Depletions in all light thermospheric species at high northern latitudes extend up to the exobase in our model simulations during the January 2013 SSW/MC period, with the largest depletions simulated for the lightest species. Further, our modeling work substantiates the paradigm of increased mixing in the MLT driven by a meridional residual circulation during SSWs resulting from enhanced small‐scale gravity wave and migrating semidiurnal tidal forcing; the former being the primary driver and the latter of secondary but notable importance in our model simulations. SSW/MC induced light species variability then gets projected upward into the thermosphere through molecular diffusion. Modeled light species variability during the January 2013 SSW/MC event suggests SSW/MC signatures could be present in the topside ionosphere and plasmasphere.
Plain Language Summary
Sudden stratospheric warmings (SSWs) and mesospheric coolings (MCs) are episodic polar middle atmospheric (∼12–80 km or ∼7–50 miles altitude) dynamical weather events driven by increased wave forcing from the troposphere. These events are known to have global effects on the meteorology of the upper atmosphere (i.e., the thermosphere and ionosphere). Observational and modeling evidence presented in this study demonstrate that SSWs and MCs in the middle atmosphere act to drive changes in the chemical composition of the upper atmosphere through an intricate series of processes, set in motion by SSW/MC enhancements in lower and middle atmospheric wave forcing. Our results show that SSW/MC driven changes in particularly light species like hydrogen extend well into the transition region between Earth's atmosphere and outer space. This implies that middle atmospheric weather may have an impact on the plasma populations several Earth radii above Earth's surface (∼10,000 miles or more away).
Key Points
Decreases in helium and atomic hydrogen concentration at high northern latitudes occur at the onset of mesospheric cooling events
Small‐scale GW and tidal activity drives enhanced meridional transport which extends light species decreases up to the exobase in TIME‐GCM
Accompanying decreases in O+ and H+ during middle atmospheric dynamical events have implications for the inner magnetosphere
The vast set of near‐global and continuous atmospheric measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument since 2002, including daytime and ...nighttime kinetic temperature (Tk) from 20 to 105 km, is available to the scientific community. The temperature is retrieved from SABER measurements of the atmospheric 15 μm CO2 limb emission. This emission separates from local thermodynamic equilibrium (LTE) conditions in the rarefied mesosphere and thermosphere, making it necessary to consider the CO2 vibrational state non‐LTE populations in the retrieval algorithm above 70 km. Those populations depend on kinetic parameters describing the rate at which energy exchange between atmospheric molecules take place, but some of these collisional rates are not well known. We consider current uncertainties in the rates of quenching of CO2(υ2) by N2, O2 and O, and the CO2(υ2) vibrational‐vibrational exchange to estimate their impact on SABER Tk for different atmospheric conditions. The Tk is more sensitive to the uncertainty in the latter two, and their effects depend on altitude. The Tk combined systematic error due to non‐LTE kinetic parameters does not exceed ±1.5 K below 95 km and ±4–5 K at 100 km for most latitudes and seasons (except for polar summer) if the Tk profile does not have pronounced vertical structure. The error is ±3 K at 80 km, ±6 K at 84 km and ±18 K at 100 km under the less favorable polar summer conditions. For strong temperature inversion layers, the errors reach ±3 K at 82 km and ±8 K at 90 km. This particularly affects tide amplitude estimates, with errors of up to ±3 K.
One of the most important dynamical processes in the tropical stratosphere is the quasi‐biennial oscillation (QBO) of the zonal wind. Still, the QBO is not well represented in weather and climate ...models. To improve the representation of the QBO in the models, a better understanding of the driving of the QBO by atmospheric waves is required. In particular, the contribution of gravity waves is highly uncertain because of the small horizontal scales involved, and there is still no direct estimation based on global observations. We derive gravity wave momentum fluxes from temperature observations of the satellite instruments HIRDLS and SABER. Momentum flux spectra observed show that particularly gravity waves with intrinsic phase speeds <30m/s (vertical wavelengths <10km) interact with the QBO. Gravity wave drag is estimated from vertical gradients of observed momentum fluxes and compared to the missing drag in the tropical momentum budget of ERA‐Interim. We find reasonably good agreement between their variations with time and in their approximate magnitudes. Absolute values of observed and ERA‐Interim missing drag are about equal during QBO eastward wind shear. During westward wind shear, however, observations are about 2 times lower than ERA‐Interim missing drag. This could hint at uncertainties in the advection terms in ERA‐Interim. The strong intermittency of gravity waves we find in the tropics might play an important role for the formation of the QBO and may have important implications for the parameterization of gravity waves in global models.
Key Points
Satellite observations of gravity waves (GWs) show QBO‐related variations
In the tropics observed GW drag agrees well with the missing drag in ERA‐Interim
GW observations hint at uncertainties in modeled advection terms
FORUM Palchetti, L.; Brindley, H.; Bantges, R. ...
Bulletin of the American Meteorological Society,
12/2020, Letnik:
101, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are ...responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 μm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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