JMSJ, 2015, Vol. 93, No. 4 (August)
Kodama et al. (2015)
Kodama, C., Y. Yamada, A. T. Noda, K. Kikuchi, Y. Kajikawa, T. Nasuno, T. Tomita, T. Yamaura, H. G. Takahashi, M. Hara, Y. Kawatani, M. Satoh, and M. Sugi, 2015: A 20-year climatology of a NICAM AMIP-type simulation. J. Meteor. Soc. Japan, 93, 393-424.
http://doi.org/10.2151/jmsj.2015-024 Graphical Abstract
- A 20-year integration by 14-km mesh Non-hydrostatic Icosahedral Atmospheric Model (NICAM) was conducted for the first time to obtain a climatological mean and diurnal-to-interannual variability of a simulated atmosphere under the Atmospheric Model Intercomparison Project (AMIP)-type conditions.
- NICAM simulates many aspects of atmospheric climatological mean state and diurnal-to-interannual variability of precipitation, clouds, radiation, and zonal mean field.
- Tropical cyclones (TCs) are detected without setting artificial thresholds of wind speed, and the number of TCs is close to that of the observed. Seasonal march of TC genesis for each ocean basin is well simulated. Statistical property of the Madden-Julian oscillation and tropical waves is well reproduced in the space-time power spectra. Asian monsoon, Baiu front, and stratospheric variability were also analyzed. Some significant model biases still exist, which indicates a need for further model improvements.
- The results of this study indicate that a high-resolution global non-hydrostatic model has the potential to reveal multi-scale phenomena in the climate system.
Oda et al. (2015)
- The interaction between westward-propagating upper Rossby and westward- and eastward-propagating lower gravity waves is examined in a simple vertical-zonal two-dimensional model. We analytically solve the initial value problem for the buoyancy and vorticity disturbances.
- For the parameter values for exponential instability, the upper Rossby wave and the lower gravity waves are phase locked and grows as an exponential function of time(Fig 1). For the parameter values for marginal instability, the solution grows as a linear function of time and asymptotically approaches an in-phase or anti-phase configuration between the upper and lower disturbances. For the parameter values for stability, the upper and lower waves are not phase-locked but pass away from each other, just like free waves.
- Although the resonant interaction occurs between the westward-propagating upper Rossby wave and the eastward-propagating lower gravity wave, the westward-propagating lower gravity wave also plays a role in the resonance. The westward-propagating gravity wave regulates the westward propagation velocity of the Rossby wave, helping the Rossby and eastward-propagating gravity waves to become phase-locked(Fig.2). By the presence of the westward-propagating gravity wave, the unstable region in the parameter space is enlarged.
Taguchi, M., 2015: On the asymmetry of forecast errors in the Northern winter stratosphere between vortex weakening and strengthening conditions. J. Meteor. Soc. Japan, 93,
http://doi.org/10.2151/jmsj.2015-029 Graphical Abstract
- The asymmetry of forecast errors in the Northern winter stratosphere between vortex weakening and strengthening conditions, suggested from previous studies, is investigated.
- One-month hindcast data of the Japan Meteorological Agency are compared to the JRA-55 reanalysis data. The vortex weakening and strengthening conditions are defined in the Polar-Jet Oscillation framework using an empirical orthogonal function analysis of JRA-55 polar stratospheric temperatures.
- Results demonstrate that forecast errors in the stratosphere are larger for the vortex weakening conditions than for the strengthening conditions (Fig. 1a). It is also shown that forecast errors in the planetary wave forcing in the upper troposphere are responsible for this feature. Namely, it is more difficult to forecast planetary wave amplification leading to the vortex weakening conditions than wave attenuation to the vortex strengthening conditions (Fig. 1b).
- Major stratospheric sudden warming events and vortex intensification events also exhibit similar asymmetry in forecast errors.
Otsuka et al. (2015)
Otsuka, M., M. Kunii, H. Seko, K. Shimoji, M. Hayashi, K. Yamashita, 2015: Assimilation experiments of MTSAT rapid scan atmospheric motion vectors on a heavy rainfall event. J. Meteor. Soc. Japan, 93, 459-475.
http://doi.org/10.2151/jmsj.2015-030 Graphical Abstract
- The impact of atmospheric motion vectors derived from MTSAT-1R 5-min rapid scan imagery (RS-AMV) on numerical forecasting of a heavy rainfall near a stationary front was investigated by conducting assimilation experiments with the JMA's operational non-hydrostatic model with 4-dimensional variational data assimilation (JNoVA).
- Assimilation experiments covering a heavy rainfall event were conducted by using different lengths of assimilation time slot and time intervals of spatial thinning for the assimilation of the RS-AMV (Table 2).
- The assimilation of RS-AMVs caused the initial wind fields to enhance upper-level divergence and low-level convergence around the front (Fig. 12), and as a result, the forecast of the rainfall amount was increased near the front and the verification scores were slightly improved over the control experiment in the early forecast hours (Fig. 11).
Hira et al. (2015)
- An analytical solution of nocturnal low level jets is presented. The present model is an extension of Blackadar who described the nocturnal low level jet as a result of an inertial oscillation (see Fig. 1).
- In the present model, the momentum equation in the daytime atmospheric boundary layer includes a term representing convective mixing in addition to a mixing with a constant diffusion coefficient.
- With the convective mixing, the daytime equilibrium wind velocity becomes vertically more uniform than the Ekman solution. In the nighttime atmospheric boundary layer, the convective mixing is assumed to be absent, and the diffusion coefficient, which is assumed to be constant, is smaller than that in the daytime. Without the convective mixing, the nighttime equilibrium wind velocity is the same as that of the Ekman solution.
- The analytical solution describes the temporal evolution of nighttime wind velocity as a damped inertial oscillation around the nighttime equilibrium wind velocity, starting from the daytime equilibrium wind velocity.
- By appropriately choosing the values of parameters in the analytical solution, already published some results are reproduced. For example, the height of maximum wind speed decreases as time goes on. There exist backward inertial oscillations in addition to the well-known forward inertial oscillations. In the lower levels, the oscillations are damped rapidly (see Fig. 2).
Notes and Correspondence
Satoh et al. (2015)
Satoh, M., Y. Yamada, M. Sugi, C. Kodama, and A. T. Noda, 2015: Constraint on future change in global frequency of tropical cyclones due to global warming. J. Meteor. Soc. Japan, 93, 489-500.
Special Edition on Contributions to Asia Oceania Atmospheric Sciences
http://doi.org/10.2151/jmsj.2015-025 Graphical Abstract
- A diagnostic relation based on the convective mass flux to constrain the global frequency of tropical cyclones is proposed.
- The simulation results with 20-year 14km-mesh NICAM showed that the future reduction in the global frequency is much larger than that of the total tropical convective mass flux.
- Either a future increase in the frequency of stronger tropical cyclones or an areal increase in strong updrafts explains the difference in the global frequency of tropical cyclones.
- This study suggests the future intensification of tropical cyclones leads to the future reduction of their frequency under the constraint that the contribution of tropical cyclone remains the same or smaller.
Fujibe, F., 2015: Comments on "Anthropogenic heat release: Estimation of global distribution and possible climate effect" by Chen, B. et al. J. Meteor. Soc. Japan, 93, 501-503.
http://doi.org/10.2151/jmsj.2015-027 Graphical Abstract
- Figs. 2 and 3 of Chen et al. (2014; C14) show a rapid increase of anthropogenic heat release in many regions of the world.
- However, existing data show no remarkable increase in energy consumption in Europe and North America (Figure 1). Also, no remarkable change is found for the intensity of night lights (SOL = sum of lights), except in China and India (Figure 2).
- There is therefore serious doubt about the validity of C14’s results.
Chen et al. (2015)
Chen, B., J.-Q. Zhao, L. Chen, G. Shi, 2015: Reply to the comments of F. Fujibe on "Anthropogenic heat release: Estimation of global distribution and possible climate effect" by Chen, B. et al. J. Meteor. Soc. Japan, 93, 505-508.
http://doi.org/10.2151/jmsj.2015-028 Graphical Abstract
- Due to the high-precision grid and unique ability to detect low levels of visible and near-infrared radiance at night, the DMSP/OLS data provides an effective way to estimate large-scale and high-resolution distribution of AHR. Above all, the results of global distribution of AHR by applying DMSP/OLS data is generally consistent with energy consumption statistics, while errors occur inevitably. This method provide us a new way to obtain credible large-scale continuous high-precision grid distribution of AHR, which is very important for the research of AHR in climate models.