High-resolution Beijing mesosphere–stratosphere–troposphere (MST) radar detection of tropopause structure and variability over Xianghe (39.75° N, 116.96° E), China

As a result of partial specular reflection from the atmospheric stable layer, the radar tropopause (RT) can simply and directly be detected by VHF radars with vertical incidence. Here, the Beijing mesosphere–stratosphere–troposphere (MST) radar measurements are used to investigate the structure and the variabilities in the tropopause in Xianghe, China, with a temporal resolution of 0.5 h from November 2011 to May 2017. The high-resolution radar-derived tropopause is compared with the thermal lapse-rate tropopause (LRT) that is defined by the World Meteorological Organization (WMO) criterion from twice-daily radiosonde soundings and with the dynamical potential vorticity tropopause (PVT) that is defined as the height of the 2 PVU (PVU – potential vorticity units; 1 PVU = 106 m2 s−1 K kg−1) surface. We only consider tropopauses below 16 km in this study because of limitations with the radar system. During all the seasons, the RT and the LRT in altitude agree well with each other, with a correlation coefficient of ≥0.74. Statistically, weaker (higher) tropopause sharpness seems to contribute to larger (smaller) difference between the RT and the LRT in altitude. The RT agrees well with the PVT in altitude during winter and spring, with a correlation coefficient of ≥0.72, while the correlation coefficient in summer is only 0.33. As expected, the monthly mean RT and LRT height both show seasonal variations. Lomb–Scargle periodograms show that the tropopause exhibits obvious diurnal variation throughout the seasons, whereas the semidiurnal oscillations are rare and are occasionally observed during summer and later spring. Our study shows the potential of the Beijing MST radar to determine the tropopause height as well as present its diurnal oscillations.

High-resolution Beijing MST radar detection of tropopause structure and variability over Xianghe (39.75° N, 116.96° E), China

As a result of partial specular reflection from the atmospheric stable layer, the radar tropopause (RT) can simply and directly be detected by VHF radars with vertical incidence. Here, the Beijing MST radar measurements are used to investigate the structure and the variabilities of the tropopause in Xianghe, China with a temporal resolution of 0.5 hour from November 2011 to May 2017. High-resolution radar-derived tropopause is compared with the thermal lapse-rate tropopause (LRT) that defined by the World Meteorological Organization (WMO) criterion from twice daily radiosonde soundings and with the dynamical potential vorticity tropopause (PVT) that defined as the height of 2 PVU surface. During all the seasons, the RT and the LRT in altitude agree well with each other with a correlation coefficient of ≥ 0.74. Statistically, weaker (higher) tropopause sharpness seems to contribute to larger (smaller) difference between the RT and the LRT in altitude. The RT agrees well with the PVT in altitude during winter and spring with a correlation coefficient of ≥ 0.72, while the correlation coefficient in summer is only 0.33. As expected, the monthly mean RT and LRT height both show seasonal variations. Lomb-Scargle periodograms show that the tropopause exhibits obvious diurnal variation throughout the seasons, whereas the semidiurnal oscillations are rare and occasionally observed during summer and later spring. Our study shows the good capability of the Beijing MST radar to determine the tropopause height, as well as present its diurnal oscillations.

Dynamical Potential Energy: A New Approach to Ocean Energetics

The concept of available potential energy is supposed to indicate which part of the potential energy is available to transform into kinetic energy. Yet it is impossible to obtain a unique definition of available potential energy for the real ocean because of nonlinearities of the equation of state, rendering its usefulness largely hypothetical. In this paper, the conservation of energy is first reformulated in terms of horizontal anomalies of density and pressure for a simplified ocean model using the Boussinesq and hydrostatic approximations. This framework introduces the concept of “dynamical potential energy,” defined as the horizontal anomaly of potential energy, to replace available potential energy. Modified conservation equations are derived that make it much simpler to identify oceanic power input by buoyancy and mechanical forces. Closed budgets of energy are presented for idealized circulations obtained with a general circulation model, comparing spatial patterns of power inputs generated by wind and thermal forcings. Finally, a generalization of the framework to compressible fluids is presented, opening the way to applications in atmosphere energetics.

Comparison and Analyses of Existing Objective, Quantificational Blocking Indices

There are existing objective, quantitative blocking indices that could be classified into five types: the departure method, the Tibaldi and Molteni（TM） method, the dynamical index(PV-θindex), the dynamical potential vorticity (PV) based index, and the circumfluent type method. Persistent blocking highs can be associated with destructive weather including low temperatures, snowfall, and anomalous freezing from January 1st to February 2nd 2008 in China. Using the daily reanalysis data provided by NCEP/NCAR, the merits and flaws of these five objective methods are studied individually, including the intensity、size and frequency of block. Generally speaking, each method has both advantages and clearly identifiable limitations because of the mathematical formulation for each objective blocking index. Based on the merits and flaws of these blocking indices summarized in this study, investigators and operational meteorologists could apply these blocking indices better if they can select an index compatible with their study objectives, or improve upon and innovate a new method.