Stochastic Modeling of Stratospheric Temperature

This study suggests a stochastic model for time series of daily zonal (circumpolar) mean stratospheric temperature at a given pressure level. It can be seen as an extension of previous studies which have developed stochastic models for surface temperatures. The proposed model is a combination of a deterministic seasonality function and a Lévy-driven multidimensional Ornstein–Uhlenbeck process, which is a mean-reverting stochastic process. More specifically, the deseasonalized temperature model is an order 4 continuous-time autoregressive model, meaning that the stratospheric temperature is modeled to be directly dependent on the temperature over four preceding days, while the model’s longer-range memory stems from its recursive nature. This study is based on temperature data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis model product. The residuals of the autoregressive model are well represented by normal inverse Gaussian-distributed random variables scaled with a time-dependent volatility function. A monthly variability in speed of mean reversion of stratospheric temperature is found, hence suggesting a generalization of the fourth-order continuous-time autoregressive model. A stochastic stratospheric temperature model, as proposed in this paper, can be used in geophysical analyses to improve the understanding of stratospheric dynamics. In particular, such characterizations of stratospheric temperature may be a step towards greater insight in modeling and prediction of large-scale middle atmospheric events, such as sudden stratospheric warming. Through stratosphere–troposphere coupling, the stratosphere is hence a source of extended tropospheric predictability at weekly to monthly timescales, which is of great importance in several societal and industry sectors.

The Response of Tropical Cyclone Intensity to Temperature Profile Change

Theory indicates that tropical cyclone intensity should respond to changes in the vertical temperature profile. While the sensitivity of tropical cyclone intensity to sea surface temperature is well understood, less is known about sensitivity to the temperature profile. In this paper, we combine historical data analysis and idealised modelling to explore the extent to which historical tropospheric warming and lower stratospheric cooling can explain observed trends in the tropical cyclone intensity distribution. Observations and modelling agree that historical global temperature profile changes coincide with higher lifetime maximum intensities. But observations suggest the response depends on the tropical cyclone intensity itself. Historical lower- and upper-tropospheric temperatures in hurricane environments have warmed significantly faster than the tropical mean. In addition, hurricane-strength storms have intensified at twice the rate of weaker storms per unit warming at the surface and at 300-hPa. Idealized simulations respond in the expected sense to various imposed changes in the temperature profile and agree with tropical cyclones operating as heat engines. Yet lower stratospheric temperature changes have little influence. Idealised modelling further shows an increasing altitude of the TC outflow but little change in outflow temperature. This enables increased efficiency for strong tropical cyclones despite the warming upper troposphere. Observed sensitivities are generally larger than modelled sensitivities, suggesting that observed tropical cyclone intensity change responds to a combination of the temperature profile change and other environmental factors.

Measurement of Ozone at Maitri, Antarctica

Regular ozone profile measurement over Antarctica has been made by India Meteorological Department since 1987 at Dakshin Gangotri and later at Maitri (70.7°S, 11.7°E) since 1990 with the help of Indian electro-chemical ozone sonde. Surface ozone measurement was also started at Dakshin Gangotri since 1989 and later at Maitri. Ozone sonde data at Dakshin Gangotri and Maitri have been analysed and ozone hole structure has been studied in detail. The drastic decrease in ozone amount is clearly seen between 100 hPa to 30 hPa layer reaching near zero value. Incidently this is the layer where highest ozone concentration occurs during other months except September-October. The ozone hole has been quite severe during 1994-95 with increase in area and depth. During 1996 the Antarctic ozone hole was also similar to previous years. An interesting feature of the 1995 event was the persistence of ozone hole through November & December. Stratospheric temperature changes during 1995 also support that the cold core vortex during 1995 was very cold and persisted up to November.

Climatology and Long-Term Trends in the Stratospheric Temperature and Wind Using ERA5

This study analyses long-term trends in temperature and wind climatology based on ERA5 data. We study climatology and trends separately for every decade from 1980 to 2020 and their changes during this period. This study is focused on the pressure levels between 100–1 hPa, which essentially covers the whole stratosphere. We also analyze the impact of the sudden stratospheric warmings (SSW), North Atlantic Oscillation (NAO), El Nino Southern Oscillation (ENSO) and Quasi-biennial oscillation (QBO). This helps us to find details of climatology and trend behavior in the stratosphere in connection to these phenomena. ERA5 is one of the newest reanalysis, which is widely used for the middle atmosphere. We identify the largest differences which occur between 1990–2000 and 2000–2010 in both temperature climatology and trends. We suggest that these differences could relate to the different occurrence frequency of SSWs in 1990–2000 versus 2000–2010.

Diurnal Cycles of Synthetic Microwave Sounding Lower-Stratospheric Temperatures from Radio Occultation Observations, Reanalysis, and Model Simulations

An observationally-based global climatology of the temperature diurnal cycle in the lower stratosphere is derived from eleven different satellites with Global Positioning System-Radio Occultation (GPS-RO) measurements from 2006-2020. Methods used in our analysis allow for accurate characterization of global stratospheric temperature diurnal cycles, even in the high latitudes where the diurnal signal is small but longer timescale variability is large. A climatology of the synthetic Microwave Sounding Unit (MSU) and Advanced MSU (AMSU) Temperature in the Lower Stratosphere (TLS) is presented to assess the accuracy of diurnal cycle climatologies for the MSU and AMSU TLS observations, which have traditionally been generated by model data. The TLS diurnal temperature ranges are typically less than 0.4 K in all latitude bands and seasons investigated. It is shown that the diurnal range (maximum minus minimum temperature) of TLS is largest over southern hemisphere tropical land in the boreal winter season, indicating the important role of deep convection. The range, phase, and seasonality of the TLS diurnal cycle are generally well captured by the WACCM6 simulation and ERA5 reanalysis. We also present an observationally-based diurnal cycle climatology of temperature profiles from 300-10 hPa for various latitude bands and seasons and compare the ERA5 reanalysis with the observations.

An Analytical Model for Spatially Varying Clear-Sky CO2 Forcing

Clear-sky CO2 forcing is known to vary significantly over the globe, but the state dependence which controls this is not well understood. Here we extend the formalism of Wilson and Gea-Banacloche (2012) to obtain a quantitatively accurate analytical model for spatially-varying instantaneous CO2 forcing, which depends only on surface temperature Ts, stratospheric temperature, and column relative humidity RH. This model shows that CO2 forcing can be considered a swap of surface emission for stratospheric emission, and thus depends primarily on surface-stratosphere temperature contrast. The strong meridional gradient in CO2 forcing is thus largely due to the strong meridional gradient in Ts. In the tropics and mid-latitudes, however, the presence of H2O modulates the forcing by replacing surface emission with RH-dependent atmospheric emission. This substantially reduces the forcing in the tropics, introduces forcing variations due to spatially-varying RH, and sets an upper limit (with respect to Ts variations) on CO2 forcing which is reached in the present-day tropics.In addition, we extend our analytical model to the instantaneous tropopause forcing, and find that this forcing depends on Ts only, with no dependence on stratospheric temperature. We also analyze the ‘τ = 1’ approximation for the emission level, and derive an exact formula for the emission level which yields values closer to τ = 1/2 than to τ = 1.

Thermal Wake Studies During the August 21st 2017 Total Solar Eclipse

A thermal wake occurs when a high altitude balloon (HAB) influences and changes the surrounding ambient atmospheric temperature of the air through which it passes. This effect warms the air below the balloon to greater than the ambient temperatures during daytime flights, and cooler than ambient temperatures during nighttime flights. The total solar eclipse of August 21st, 2017, provided us with an opportunity to study these balloon induced temperature transitions from daytime, to eclipsed induced night conditions over the scale of a single flight. To measure these transitions, St. Catherine University and the University of Minnesota, Morris, flew over 40 temperature sensors suspended beneath weather balloons ascending within the path of totality. Stratospheric temperature data collected during the eclipse show evidence of both daytime and nighttime wake temperature profiles.

Neptune's Atmospheric Structure from the Spitzer Infrared Spectrometer

<p><strong>Introduction:</strong> NASA’s Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5 - 37 micron) disc-averaged spectra of Neptune in May 2004, November 2004, November 2005, and May 2006. Meadows et al., (2008, doi: 10.1016/j.icarus.2008.05.023) discovered Neptune's complex hydrocarbons methylacetylene and diacetylene and derived their abundances using the May 2004 data. The rest of the Neptune data has yet to be published. The data have all been reduced using the same methodology as Rowe-Gurney et al., (2021, doi: 10.1016/j.icarus.2021.114506) used for Uranus, so that each year can be reliably compared.</p> <p>We detect the same hydrocarbons seen in Meadows et al., (2008). This includes the strongest bands of methane (CH<sub>4</sub>), acetylene (C<sub>2</sub>H<sub>2</sub>) and ethane (C<sub>2</sub>H<sub>6</sub>) as-well-as weaker but still clearly recognisable features of ethylene (C<sub>2</sub>H<sub>4</sub>), carbon dioxide, methyl (CH<sub>3</sub>), methylacetylene (C<sub>3</sub>H<sub>4</sub>) and diacetylene (C<sub>4</sub>H<sub>2</sub>).</p> <p>At Uranus, there was a considerable longitudinal variation in stratospheric emission detected in the Spitzer data for multiple epochs (Rowe-Gurney et al., 2021). A variation is not present at Neptune in 2005 or late 2004, when all the separate longitudes displayed the same brightness temperature. In May 2004 a stratospheric variation is present, although it is tentative due to the deviation only appearing at a single longitude and because there are larger uncertainties on this early dataset. If the variation is real then it could be caused by stratospheric methane injection associated with convective clouds or perturbations to the location of the south polar warm vortex (Orton et al., 2012, doi: 10.1016/j.pss.2011.06.013).</p> <p><strong>Optimal Estimation Retrievals: </strong>The data from 2005 have optimised exposure times, multiple observed longitudes, and therefore the lowest noise. It is this data we are using to derive the vertical structure of the temperature and composition in the stratosphere and upper troposphere (between around 1 nanobar and 2 bars of pressure). We present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008, doi: 10.1016/j.jqsrt.2007.11.006) of the globally averaged November 2005 data with the aim of constraining the temperature profile and the abundances of the stratospheric hydrocarbons. We fit both the low-resolution (R~120) and high-resolution (R~600) module data, testing multiple temperature priors derived from chemical models (Moses et al., 2018, doi: 10.1016/j.icarus.2018.02.004) and observations from AKARI (Fletcher et al., 2010, doi: 10.1051/0004-6361/200913358). Initial findings show that we are sensitive to stratospheric D/H ratio (derived from the relative abundances of CH<sub>4</sub> and CH<sub>3</sub>D) and therefore we will attempt to constrain this value by finding the best fit for our model.</p> <p><strong>Conclusion:</strong> Full spectrum mid-infrared data from Neptune in 2005 taken by the Spitzer Infrared Spectrometer is to be analysed using optimal estimation retrievals for the first time. The globally-averaged stratospheric temperature structure and the abundances of stratospheric hydrocarbons will be determined along with the ratio of D/H. The disc-averaged thermal and chemical structure from Spitzer will likely be our best characterisation of Neptune’s thermal structure until JWST/MIRI acquired spatially-resolved mid-infrared spectroscopy in 2022.</p>