Mesopause Region Temperature Research Articles

Pseudorandom modulation continuous-wave narrowband sodium temperature and wind lidar

Abstract. We report the first pseudorandom modulation continuous-wave (PMCW) narrowband sodium temperature and wind lidar developed at the University of Science and Technology of China (USTC). The laser system uses a 1178 nm diode seed laser and a fiber Raman amplifier with a fiber-coupled acousto-optic frequency shifter (AOFS) to generate a narrowband 589.158 nm light with an output power of 1.5 W at three frequencies of v0, v+, and v−. Based on an innovative technique and algorithm, the main beam and the residual beam modulated by electro-optic modulator (EOM) with M pseudorandom sequence code (M-code) are separately directed to the vertical and eastward directions. The three-frequency light is designed in timing with the multiple-period 127-bit M-code groups. The uncertainties of the temperature and wind with the vertical and temporal resolutions of 1 km and 30 min under clear-sky conditions are estimated to be 5.0 K and 10 m s−1, respectively, at the sodium peak. The temperature and wind results are in good agreement with those observed by satellite and nearby ground-based meteor radar, demonstrating the reliability of the PMCW narrowband sodium lidar system for measuring the mesopause region's temperature and wind.

Climatology and Seasonal Variations of Temperatures and Gravity Wave Activities in the Mesopause Region Above Ft. Collins, CO (40.6°N, 105.1°W)

AbstractUtilizing 956 nights of Na lidar nocturnal mesopause region temperature profiles acquired at Fort Collins, CO (40.6°N, 105.1°W) over a 20‐year period (March 1990–2010), we deduce background nightly mean temperature and the square of the buoyancy frequency N2(z) at 2‐km resolution between 83 and 105 km. The temperature climatology reveals the two‐level mesopause structure with clarity and sharp mesopause transitions, resulting in 102 days of summer from Days 121 to 222 of the year. The same data set analyzed at 10‐min and 1‐km resolution gives the gravity wave (GW) temperature perturbations Ti'(z) and the wave variance Var(T′(z)) and GW potential energy Epm(z) between 85 and 100 km. Seasonal averages of GW Var(T′(z)) and Epm(z) between 90 and 100 km, show that Var(T′) for spring and autumn are comparable and lower than for summer and winter. Due mainly to the higher background stability, or larger N2(z) in summer, Epm(z) between 85 and 100 km is comparable in spring, summer, and autumn seasons, but ∼30%–45% smaller than the winter values at the same altitude. The uncertainties are about 4% for winter and about 5% for the other three seasons. The values for Epm are (156.0, 176.2, 145.6, and 186.2 J/kg) at 85 km for (spring, summer, autumn, and winter) respectively, (125.4, 120.2, 115.2, and 168.7 J/kg) at 93 km, and (207.5, 180.5, 213.1, and 278.6 J/kg) at 100 km. Going up in altitude, all profiles first decrease and then increase, suggesting that climatologically, GWs break below 85 km.

Solar Response and Long‐Term Trend of Midlatitude Mesopause Region Temperature Based on 28 Years (1990–2017) of Na Lidar Observations

AbstractWe present midlatitude solar response and linear trend from Colorado State University/Utah State University Na lidar nocturnal temperature observations between 1990 and 2017. Along with the nightly mean temperatures (_Ngt), we also use the corresponding 2‐hr means centered at midnight (_2MN), resulting in vertical trend profiles similar in shapes as those previously published. The 28‐year trend from _Ngt (_2MN) data set starts from a small warming at 85 km, to cooling at 87 (88) km, reaching a maximum of 1.85 ± 0.53 (1.09 ± 0.74) at 92 (93) km and turns positive again at 102 (100) km. The 6‐month winter trend is much cooler than the 4‐month summer trend with comparable solar response varying around 5 ± 1 K/100 SFU throughout the profile (85–105 km) with higher summer values. We explore the observed summer/winter trend difference in terms of observed gravity wave heat flux heating rate at a nearby station and the long‐term trend of gravity wave variance at a midlatitude. Between 89 and 100 km, the lidar trends are within the error bars of the Leibniz Middle Atmosphere (LIMA) summer trends (1979–2013), which are nearly identical to the lidar‐Ngt trend. We address the need of long data set for reliable analysis on trend, the extent of trend uncertainty due to possible tidal bias, the effect of a Pinatubo/episodic function, and the impact of stratospheric ozone recovery.

Comparison subpolar mesopause OH(6-2) temperature over Yakutia with the calculated data of NRLMSISE-00 model for 1999-2015

The analysis of changes in temperature of mesopause region based on fluctuation measurements of rotational temperature and intensity of molecular emission of hydroxyl OH (6-2) excited at ∼87 km altitude is presented. Observations were carried out at the Maimaga station (63°N, 129.5°E), at a distance of 120 km to the north from Yakutsk. Measurements were conducted with a digital infrared spectrograph. The temperature was determined from the distribution of the emission intensity in the different branches of the molecular hydroxyl band. Comparison OH(6-2) temperature with the calculated data of NRLMSISE-00 model was defined based on the data received from 1999 to 2015. 2320 midnight temperature values of hydroxyl OH (6-2) suitable for comparison were obtained at the Maimaga station over 16 years of measurements. The NRLMSISE-00 model describes temperature changes at the height of the mesopause region from October to April within the experimental fluctuations with a seasonal temperature variation of ∼ 35 K, deviations from the experimental values are no more than 7 ± 4 K. A correlation analysis was performed to compare the rotational temperature OH (6-2) and the NRLMSISE-00 model calculations. When the number of observations at the station Maimaga more than 180 days (about six months) correlation coefficient R> 0.7. This means that the NRLMSISE-00 model accurately describes the temperature changes of the subauroral mesopause.

Mesopause region temperature variability and its trend in southern Brazil

Abstract. Nowadays, the study of the upper atmosphere is increasing, mostly because of the need to understand the patterns of Earth's atmosphere. Since studies on global warming have become very important for the development of new technologies, understanding all regions of the atmosphere becomes an unavoidable task. In this paper, we aim to analyze the temperature variability and its trend in the mesosphere and lower thermosphere (MLT) region during a period of 12 years (from 2003 to 2014). For this purpose, three different heights, i.e., 85, 90 and 95 km, were focused on in order to investigate the upper atmosphere, and a geographic region different to other studies was chosen, in the southern region of Brazil, centered in the city of Santa Maria, RS (29∘41′02′′ S; 53∘48′25′′ W). In order to reach the objectives of this work, temperature data from the SABER instrument (Sounding of the Atmosphere using Broadband Emission Radiometry), aboard NASA's Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite, were used. Finally, two cases were studied related to distinct grids of latitude/longitude used to obtain the mean temperature profiles. The first case considered a grid of 20∘ × 20∘ lat/long, centered in Santa Maria, RS, Brazil. In the second case, the region was reduced to a size of 15∘ × 15∘ in order to compare the results and discuss the two cases in terms of differences or similarities in temperature trends. Observations show that the size of the geographical area used for the average temperature profiles can influence the results of variability and trend of the temperature. In addition, reducing the time duration of analyses from 24 to 12 h a day also influences the trend significantly. For the smaller geographical region (15∘ × 15∘) and the 12 h daily time window (09:00–21:00 UT) it was found that the main contributions for the temperature variability at the three heights were the annual and semi-annual cycles and the solar flux influence. A smaller trend (−0.02 ± 0.16 % decade−1) was found at 90 km height and small positive trends (0.58 ± 0.26 % and 0.41 ± 0.19 % decade−1) were found at altitudes of 85 and 95 km, respectively.. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; pressure, density, and temperature) – meteorology and atmospheric dynamics (climatology)

Unexpected East-West effect in mesopause region SABER temperatures over El Leoncito

We find that mesopause region temperatures determined by the SABER instrument on the TIMED satellite during nocturnal overpasses at El Leoncito (31.8°S, 69.3°W) are several kelvins higher when SABER observes from the East than when it observes from the West. We distinguish between altitudes corresponding to the nominal emission heights of the OH and O2 airglow layers. The East-West temperature differences of 4.5K obtained for OH-equivalent height, and of 3.5K for O2-equivalent height are surprising, because an effect of the South Atlantic Anomaly on SABER temperature is unexpected. However, the ground-based data obtained with our airglow spectrometer at El Leoncito show that such a SABER artifact can be ruled out. Rather, the phenomenon is explained as a consequence of the temporal sampling of the nocturnal variation, which is mostly due to the semidiurnal tide. The monthly mean tide is strongest from April to September with a mean amplitude of 6.9K for OH, and of 10.5K for O2 rotational temperature, but the contribution to the East-West effect varies strongly from month to month because of differences in the temporal sampling. This mechanism should be active at other sites, as well.

Retrieving mesopause temperature and line-of-sight wind from full-diurnal-cycle Na lidar observations.

Narrowband Na lidar measurement of mesopause region temperatures were pioneered by Fricke and von Zahn in 1985, in 1990 by She et al. at Colorado State University (CSU), with upgrades to measure both temperature and wind in 1994, and under sunlit conditions in 1996 with 24 h continuous observational capability in 2002. This paper details the assumptions and procedures for the retrieval of mesopause region temperatures, line-of-sight winds, and sodium densities from day and night signals from the CSU narrowband Na lidar. The Hanle effect and the effect of the pulsed laser line shape function on the accuracy of temperature and LOS wind retrieval are also discussed.

Long-term midlatitude mesopause region temperature trend deduced from quarter century (1990–2014) Na lidar observations

Abstract. The long-term midlatitude temperature trend between 85 and 105 km is deduced from 25 years (March 1990–December 2014) of Na Lidar observations. With a strong warming episode in the 1990s, the time series was least-square fitted to an 11-parameter nonlinear function. This yields a cooling trend starting from an insignificant value of 0.64 ± 0.99 K decade−1 at 85 km, increasing to a maximum of 2.8 ± 0.58 K decade−1 between 91 and 93 km, and then decreasing to a warming trend above 103 km. The geographic altitude dependence of the trend is in general agreement with model predictions. To shed light on the nature of the warming episode, we show that the recently reported prolonged global surface temperature cooling after the Mt Pinatubo eruption can also be very well represented by the same response function.

Simpson's paradox in trend analysis: An example from El Leoncito airglow data

[1] We use our mesopause region temperature data from El Leoncito (31.8°S, 69.3°W) to illustrate how the increased length of the data set alone does not simplify trend analysis. This is because the adequate interpretation of trend results does not only depend on the statistical characteristics of the data time series. A longer data set may make unexpected features stand out, which require an explanation before definite conclusions on long-term trends can be drawn. While the rotational temperatures derived at El Leoncito from the OH(6–2) airglow band appear rather homogeneous at first sight, the O2 temperatures measured with the same instrument and optical filter exhibit features strongly reminiscent of Simpson's classical statistical paradox, in that straightforward trends derived from parts show signs opposite to those of the complete data set. The resolution of this paradox requires more efforts to diagnose and remove the impact of instrumental artifacts besides taking any other geophysical variation that does not directly contribute to long-term change into account. Intercomparison with other instruments is certainly useful but may warrant the elimination of new uncertainties discovered in the act.

Noctilucent cloud variability and mean parameters from 15 years of lidar observations at a mid‐latitude site (54°N, 12°E)

Noctilucent clouds (NLC) are an important tracer of temperature and dynamics of the summer mesopause region. Our site at Kühlungsborn (Germany, 54°N) is at the equatorward edge of the NLC region and therefore of special interest for the understanding of these clouds. 41 nights (63 h) of NLC are observed since 1997. They form the largest lidar data set from mid‐latitudes. NLC are typically weak, with nearly 70% having a backscatter coefficient βmax,532nm<2 ⋅ 10−10 m−1 sr−1. The seasonal variation of NLC shows maximum occurrence around the temperature minimum (saturation maximum) but lower temperatures (higher saturation) at the beginning compared to the end of the season. Mean centroid altitude is 82.7 ± 0.03 km, with strong NLC being typically lower and vertically thinner compared to weak clouds. NLC occurrence was lowest in the years 2000–2002 and reached a maximum in 2009 with a rate of 19%. Overall, NLC are less frequent and dimmer compared to higher latitudes. The occurrence is highly anti‐correlated with solar activity. Beside NLC, we are measuring mesospheric temperatures since 2002 by lidars, complemented by microwave observations of water vapor (since October 2009) and radar observations of mesospheric winds. NLC occurrence is found anti‐correlated with ambient temperatures (r = −0.85 at 84 km), while low temperatures are necessary but not sufficient for individual events. Meridional winds at 84 km are weakly anti‐correlated with NLC occurrence (r = −0.58 at 84 km). Furthermore, we find some biennial variation of NLC occurrence in part of the time series. Any additional trend has not yet been detected.

Experimental evidence of a stratospheric circulation influence on mesospheric temperatures and ice-particles during the 2010–2011 austral summer at 69°S

A significant inter-annual decrease in polar mesosphere ice-particles, i.e., PMSE and PMC, during 2010–2011 is compared with earlier austral summers, in particular with 2009–2010. The first IAP iron lidar temperature measurement at Davis (68.6°S), Antarctica from 14 December 2010 are used to assess thermal effects of atmospheric processes on the mesopause region. We report low average temperatures of ∼125K measured by Fe-lidar near 90km when the PMSE season commenced, whereas temperatures were warmer in 2010–2011 compared to 2009–2010 at altitudes where PMSE normally occur (around 86km). Summer mesopause region temperature anomalies are derived using Aura MLS records. We reveal that the late break-down of the Antarctic stratospheric polar vortex on 5 January 2010, coupled with enhanced early summer mesospheric zonal wind field, provide a barrier to upward propagation of atmospheric gravity waves to be the main mechanism for the observed warm early summer season below the mesopause. The mesopause in 2010–2011 was unusually high and cold. We conclude that the timing of the annual break-down of the southern polar stratospheric vortex as manifest in zonal winds at 30hPa impacts mesosphere temperature and ice-particle formation early in the austral summer.

Narrowband sodium lidar for the measurements of mesopause region temperature and wind

We report here a narrowband high-spectral resolution sodium temperature/wind lidar recently developed at the University of Science and Technology of China (USTC) in Hefei, China (31.5 °N, 117 °E). Patterned after the Colorado State University (CSU) narrowband sodium lidar with a dye laser-based transmitter, the USTC sodium temperature/wind lidar was deployed with a number of technical improvements that facilitate automation and ease of operation; these include a home constructed pulsed dye amplifier (PDA), a beam-steering system, a star-tracking program, and an electronic timing control. With the averaged power of ∼1.2 W output from PDA and the receiving telescope diameter of 0.76 m, our lidar system has a power aperture product of ∼0.55 Wm(2) and is comparable to the CSU and the University of Illinois at Urbana-Champaign (UIUC) sodium lidar systems. The uncertainties of typical measurements induced by photon noise and laser locking fluctuation for the temperature and wind with a 2 km vertical and 15 min temporal resolutions under the nighttime clear sky condition are estimated to be ∼1.0 K and ∼1.5 m/s, respectively, at the sodium peak (e.g., 91 km), and 8 K and 10 m/s, respectively, at both sodium layer edges (e.g., 81 km and 105 km). The USTC narrowband sodium lidar has been operated regularly during the night since November 2011. Using the initial data collected, we demonstrate the reliability and suitability of these high resolution and precision datasets for studying the wave perturbations in the mesopause region.

Seasonal variations of midlatitude mesospheric Na layer and their tidal period perturbations based on full diurnal cycle Na lidar observations of 2002–2008

The Na lidar facility at Colorado State University (41°N, 105°W) started the full diurnal cycle observations of mesopause region temperature and zonal and meridional winds as well as mesospheric Na density in May 2002. In this paper, monthly means and seasonal variations of the density of mesospheric Na based on lidar observations from May 2002 to December 2008 are reported along with the amplitude and phase of tidal period perturbations. The revealed seasonal behaviors of mesospheric Na layer are generally consistent with published nocturnal climatology, with thick layers and high abundance in winter but thin layers and low abundance near summer. Tidal amplitudes of Na density are large in February–April and August–November with a dominant peak between 85 and 90 km; they are weak in summer months (May–July). The Na density tidal phase profiles, while showing downward progression, show a significant and abrupt phase shift (ideally 180 degrees). The center altitude of this phase shifting (termed switching altitude) is found to coincide with the fractional tidal amplitude (tidal amplitude over diurnal mean) minimum about 2–4 km above the centroid altitude of the associated Na layer. Taking advantage of the established temperature tidal climatology deduced from the same data set, the tidal phase behaviors between temperature and Na density and associated fractional Na density tidal amplitudes are discussed in terms of the theoretical prediction by Gardner and Shelton (1985).

Mesopause region temperature and wind measurements with pseudorandom modulation continuous-wave (PMCW) lidar at 589 nm: Erratum

Mesopause region temperature and wind measurements with pseudorandom modulation continuous-wave (PMCW) lidar at 589 nm: Erratum

Mesopause-region temperature and wind measurements with pseudorandom modulation continuous-wave (PMCW) lidar at 589 nm

A study on the feasibility of using pseudorandom modulation continuous-wave (PMCW) Na lidar for mesopause-region temperature and horizontal wind measurements is presented with a number of specific geometries and associated beam-telescope overlap functions, suitable for ground-based and airborne deployments. The performance of these deployment scenarios is analyzed by scaling from the received signal and sky background and the measurement uncertainties in temperature and horizontal wind of the well-tested Colorado State University pulsed Na lidar. Using currently available high-power (~20 W) continuous-wave Na narrowband lasers, a compact PMCW bistatic Na lidar system can indeed be deployed to simultaneously measure mesopause-region temperature and horizontal winds on a 24 h continuous basis, weather permitting.

Uncertainties in mesopause temperature trend over Fort Collins, Colorado (41°N, 105°W), using the bootstrap Monte Carlo method

[1] Two methods, based on different assumptions, have been investigated for computing the uncertainty in the trend of 960 mesopause region temperature profiles taken over 20 years. In addition to the trend, the fitting model includes annual and semiannual variations, a solar effect, and an episodic term that can be associated with the Mount Pinatubo volcanic eruption. In our standard procedure we assume that the unknown uncertainties of each measurement, and thus the weights of the observations, are constant with time and are determined by assuming that we have a good model. In addition we investigate including second derivatives along with first derivatives of the Hessian matrix. In the Monte Carlo bootstrap method one resamples the data with replacement to obtain new data sets which are fit to the model and yield a distribution of fitting parameters. The standard deviation of the distribution for a parameter is taken to be the uncertainty in the parameter. A possible assumption to justify this method is that the data are “independent and identically distributed.” Although we have not been able to justify the assumptions of either method, the two methods support each other since they give essentially the same results.

Mesopause temperatures during the polar mesospheric cloud season

[1] For the first time OSIRIS has derived and analyzed mesopause region temperatures at the summer poles. Temperatures have been derived from observations of O2 A-band emission spectra, with a typical estimated accuracy of better than ±3 K at altitudes near 90 km. The current results show that OSIRIS temperatures near the mesopause are usually ∼10 K colder than CO2 temperature results from the SABER instrument on board the TIMED satellite, however the difference between OSIRIS temperatures and SOFIE ice temperatures agrees well with previous model results, and OSIRIS temperatures are consistent with potassium lidar derived atmospheric temperatures. Between 2003–2010, the retrieved OSIRIS polar summer mesopause temperatures are often below 120 K, and on 16 January 2008, at 80°S and 223°E, a temperature of 91 ± 6 K was retrieved at an altitude of 92 km.

Long-term trends in the temperature of the mesosphere/lower thermosphere region: 2. Solar response

Understanding trends in any atmospheric quantity typically requires the ability to distinguish between naturally occurring processes that result in trends, such as the 11 year solar cycle, and potential anthropogenic secular trends that occur simultaneously. After the review of mesospheric and lower thermospheric temperature response to solar activity by Beig et al. (2008), a few new results along with some modified results by revisiting the older data sets have been reported recently. Main improvement is due to the length of data series and amount of data which have been accounted in recent years. This article summarizes the progress made in the field of temperature variability due to changing solar activity as reported recently. Recent investigations revealed that the solar signal becomes stronger with increasing latitude in the mesosphere. Temperature response to solar activity at the lower part of mesopause region is around a few degrees per 100 solar flux units (sfu), which becomes stronger (4-5 K/100 sfu) in the upper part of this region in both hemispheres. The overall global picture indicates that the solar signal in the mesopause region temperature in the Northern Hemisphere is relatively stronger in recent time in a majority of locations compared to results reported in earlier reviews.

Mesopause region temperature structure observed by sodium resonance lidar

Mesopause region temperature measurements made with a sodium resonance lidar show two unexpected features: (1) Strong positive temperature gradients are often associated with strong gradients in the sodium concentration and (2) positive temperature gradients are generally much stronger than negative ones. Although the structures we see frequently appear to be associated with gravity waves or tides, the asymmetrical temperature oscillations cannot be explained as the result of simple wave propagation. We suggest that strong positive temperature gradients correspond to regions of high atmospheric stability, where eddy diffusion is inhibited, permitting the build-up of strong gradients in temperature and minor constituent mixing ratio.

Seasonal variability in mesopause region temperatures over Fort Collins, CO (41°N, 105°W) based on lidar observations, 1990 through 2007

Nearly 900 nocturnal temperature profiles (85–105 km) from the Colorado State University Na lidar at Fort Collins, CO (40.59N, 105.14W) from 1990 to 2007. After the removal of an episodic warming attributable to Mt. Pinatubo eruption, the time series is analyzed as the sum of the climatological mean, annual and semiannual oscillation, solar cycle effect and trends along with possible annual/semiannual modulation of the latter two. The direct seasonal variation is consistent with the concept of the two-level mesopause. The trends in summer and winter are comparable 90–96 km at ∼−0.15±0.1 K/year. The summer trend turns positive above 96 km. The winter trend is negative with minimum of ∼−0.3 K/year at ∼100 km but positive at ∼104 km. The negative trend values are a factor of five smaller than an earlier analysis of the early part of this data due to removal of an episodic event.