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.

A simple thermodynamical model to estimate the rate of depletion of nocturnal low level inversion layer

The low level inversion, be it that of ground based or elevated, plays a significant role in the dispersion of polluted particles and in aviation meteorology. The rate of rise of the ground based inversion top and the base of elevated inversion causes the decrease of inversion strength and thereby permits vertical mixing of pollutants as the stability of the atmosphere is reduced. A simple thermodynamical model using the global radiation and vertical temperature profile has been proposed to estimate the rate of rise of (i) the ground based inversion top and (ii) the base of the elevated inversion. The depth of inversion thus estimated can be used in the pollution/fog dispersion models. The model is simple and operationally practicable. The limitations of the model are also discussed.

On the relationship of energetic particle precipitation and mesopause temperature

Energetic particle precipitation (EPP) has the potential to change the neutral atmospheric temperature in the mesopause region. However, recent results are inconsistent, leaving the mechanism and the actual effect still unresolved. In this study we have searched for electron precipitation events and investigated a possible correlation between D-region electron density enhancements and simultaneous neutral temperature changes. The rotational temperature of the excited hydroxyl (OH) molecules is retrieved from the infrared spectrum of the OH airglow. The electron density is monitored by the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar. We use all available experiments from the International Polar Year (IPY) in 2007–2008 until February 2019. Particle precipitation events are characterized by rapid increases in electron density by a factor of 4 at an altitude range of 80–95 km, which overlaps with the nominal altitude of the infrared OH airglow layer. The OH airglow measurements and the electron density measurements are co-located. Six of the 10 analysed electron precipitation events are associated with a temperature decrease of 10–20 K. Four events were related to a temperature change of less than 10 K. We interpret the results in terms of the change in the chemical composition in the mesosphere. Due to EPP ionization the population of excited OH at the top of the airglow layer may decrease. As a consequence, the airglow peak height changes and the temperatures are probed at lower altitudes. The observed change in temperature thus depends on the behaviour of the vertical temperature profile within the airglow layer. This is in agreement with conclusions of earlier studies but is, for the first time, constructed from electron precipitation measurements as opposed to proxies. The EPP-related temperature change recovers very fast, typically within less than 60 min. We therefore further conclude that this type of EPP event reaching the mesopause region would only have a significant impact on the longer-term heat balance in the mesosphere if the lifetime of the precipitation was much longer than that of an EPP event (30–60 min) found in this study.

Novel Method for the Estimation of Vertical Temperature Profiles Using a Coastal Acoustic Tomography System

Systems based on remote sensing technology, which use reciprocal acoustic signals to continuously monitor changes in the coastal oceanic environment, are referred to as coastal acoustic tomography (CAT) systems. These systems have been applied in regions in which heavy ship traffics, fishing and marine aquaculture activities make it difficult to establish in situ oceanic sensor moorings. Conventionally, CAT measurements were used to successfully produce horizontal maps of the depth-averaged current velocity and temperature in these coastal regions without attempting to produce a vertical temperature profile. This prompted us to propose a new method for vertical temperature profile estimation (VTPE) from CAT data using the available sea surface temperature (SST), near-bottom temperature (NBT), and water depth. The VTPE method was validated using data-assimilated and tide-included high-resolution ocean model outputs, including tide data, by comparing the estimated and simulated temperatures. Measurements were performed in the southern coastal region of Korea, where two CAT stations were moored to establish a continuous coastal ocean monitoring system. The validation results revealed that the algorithm performed well across all seasons. Sensitivity tests of the VTPE method with reasonable realistic random errors in the SST, NBT, and acoustic travel time measurements demonstrate that the method is applicable to CAT observation data because the monthly mean root-mean-squared difference (RMSD) for the vertical profiles for February, May, August, and November were 0.23, 0.30, 0.50, and 0.24°C, respectively. The VTPE method was applied to the CAT observation datasets acquired in February and August. The transceivers at the CAT stations were at depths 11 and 6 m on average. The RMSD between the estimated and observed temperatures in the middle layer (∼3 m depth) between two stations in February and August were 0.08 and 0.60°C, respectively, the accuracy of which is sufficient in largely time-varying coastal environments. We provide a novel method for continuous coastal subsurface environmental monitoring without interrupting maritime traffic, fishing, and marine aquaculture activities.

Sensitivity of steady states in a degenerately damped stochastic Lorenz system

We study stability of solutions for a randomly driven and degenerately damped version of the Lorenz ’63 model. Specifically, we prove that when damping is absent in one of the temperature components, the system possesses a unique invariant probability measure if and only if noise acts on the convection variable. On the other hand, if there is a positive growth term on the vertical temperature profile, we prove that there is no normalizable invariant state. Our approach relies on the derivation and analysis of nontrivial Lyapunov functions which ensure positive recurrence or null-recurrence/transience of the dynamics.

SIMO v1.0: Simplified model of the vertical temperature profile in a small warm monomictic lake

A simple 1-D energy budget model (SIMO) for the prediction of the vertical temperature profiles in small, monomictic lakes forced by a reduced number of input meteorological variables is proposed. The model estimates the net heat flux and thermal diffusion using only routinely measured hourly mean meteorological variables (namely, the air temperature, relative humidity, atmospheric pressure, wind speed, and precipitation), hourly mean ultraviolet B radiation (UVB), and climatological monthly mean cloudiness data. Except for the initial vertical temperature profile, the model does not use any lake-specific variables. The model performance was evaluated against lake temperatures measured continuously during an observational campaign in two lakes belonging to the Plitvice Lakes, Croatia (Lake 1 and Lake 12). Temperatures were measured at 15 and 16 depths ranging from 0.2 to 27 in Lake 1 (maximum depth of 37.4 m) and 0.2 to 43 m in Lake 12 (maximum depth of 46 m). A sensitivity analysis of the simulation length was performed for simulation lengths from 1 to 30 days. The model performed reasonably well and it was able to satisfactorily reproduce the vertical temperature profile at the hourly scale, the deepening of the thermocline with time, and the annual variation in the vertical temperature profile. A yearlong simulation initiated with an approximately constant vertical profile of the lake temperature (≈ 4 °C) was able to reproduce the onset of stratification and convective overturn. However, the thermocline depth was underestimated while the epilimnion temperatures were overestimated. Nevertheless, the values of the model performance measures obtained for a yearlong simulation were comparable with those reported for other more complex models. Thus, the presented model can be used for the assessment of the onset and duration of lake stratification periods when water temperature data are unavailable, which can be useful for various lake studies performed in other scientific fields, such as biology, geochemistry, and sedimentology.