The relationship between the carbon balance of terrestrial ecosystems and climate anomalies in 1998, the warmest year since 1860, was investigated by means of a mechanistic global biosphere model (Sim-CYCLE) based on the plant-production theory. We simulated the monthly time-series and spatial distribution of atmosphere-biosphere CO2 exchange from 1961 to 1998, based on the Sim-CYCLE by inputting the NCEP/NCAR-reanalysis climate data at the spatial resolution of T62 (containing 5828 land pixels after the Matthews biome map). The peculiar climate conditions in 1998, i. e., strong ENSO event and global warming (+0.58°C above the long-term mean), resulted in a remarkable anomaly (as much as 2.7PgC yr-1 of net emission) via the accelerated plant respiration and soil decomposition. The strong sources were in eastern Siberia, northern South America, and South Africa. This anomaly, equivalent to +1.26ppmv yr-1 of an increase rate of atmospheric CO2 concentration, can be a major cause of the extraordinarily high CO2 increase rate in 1998.
Axial and equatorial atmospheric angular momentum (AAM) functions for the rotational dynamics of the Earth are calculated monthly from ensemble mean data of three independent 40-year simulations during 1955-1994 by the global model of the Japan Meteorological Agency (JMA) forced by observed near-global sea surface temperature (SST) conditions. The model results are compared with those from the reanalysis data of the National Centers for Environmental Prediction (NCEP) and the operational objective analysis data of JMA and with the functions inferred from the observed length of day (LOD) and polar motion. The annual term of the simulated axial wind AAM function (dimensionless relative angular momentum of atmosphere due to zonal wind) during 1984-1994 agrees well with those from the two analysis data sets and roughly with the inferred function from LOD, while the semi-annual term is considerably over-estimated, suggesting an incompleteness in the simulated subtropical zonal winds. The annual term of the simulated equatorial pressure AAM function (dimensionless atmospheric inertia products due to atmospheric mass redistribution) is considerably over-estimated with respect to those from the two analysis data sets, presumably due to the large simulated redistribution of atmospheric mass between the Eurasian continent and the North Pacific Ocean. For interannual variations during 1955-1994, only the axial wind AAM function is reasonably simulated and shows good agreement with that from NCEP data as well as the Southern Oscillation Index. The above results lead to an understanding that the SST-forced AGCM simulates reasonably the atmospheric axial modes exciting LOD change but not the equatorial (non-axial) modes exciting the polar motion.
High time-resolution data observed with L-band boundary layer radar in the equatorial region of Indonesia during dry season periods have been analyzed. The existence of tropical sea-breeze circulation, whose delectability has been reported in earlier works, is corroborated by performing intercomparisons with rawinsonde and surface meteorological measurements. In addition to well defined circulation, anomalously weak echo patterns corresponding to the induced shear flow is also found to appear in several cases. Its origin can be identified as Kelvin-Helmholtz type of instability which is believed to generate long lived turbulence activity that caused the gradient of potential refractive index to be locally minimum. After seabreeze intrusion, the planetary boundary layer is divided into layers with different characteristics and cannot be considered as a homogeneous atmosphere throughout the daytime. Although quantitative comparison has not been done, it is found that the observed sea-breeze scales do not seem to critically depend on Coriolis factor f as a primary scaling parameter.
The large- and meso-α-scale features of the active Meiyu/Baiu front 1-10 July 1991 are studied by utilizing mainly the Geostationary Meteorological Satellite (GMS) IR data and ECMWF re-analysis data. The intense Meiyu/Baiu frontal precipitation occurs over the Yangtze River Basin in association with the westward elongation of the North Pacific subtropical anticyclone. The intense precipitation zone of -500km width extends from the eastern foot of the Tibetan Plateau to the western North Pacific. The frontal zone is characterized by intense precipitation, low-level jet stream, nearly moist neutral stratification and strong gradient of equivalent potential temperature θe. The large-scale confluence/convergence in the frontal zone sustains strong gradient of θe against the sink of θe due to the convective transport. The differential advection of θe generates the convective instability against the stabilizing effect of the convection, and thus, the moist neutral stratification is sustained during the period of intense convective rainfalls. The strong condensation heating is one of the factors to sustain the ascent motion in the frontal zone. The strong low-level convergence in the frontal zone is accompanied by the northward strong ageostrophic wind, which is associated with the strong acceleration along the northwestern periphery of the westward protruding subtropical anticyclone. The intrusion of the mid-latitude disturbances into the frontal zone, which occurs in the vicinity of the cut off vortex, enhances the precipitation in the frontal zone by inducing the ascent motion, the cold and dry advection. The largest diurnal variation of convective clouds is found in 90-100°E. Within the heavy rainfall zone, such significant diurnal variation is not seen, whereas the eastward passage of meso-α-scale cloud systems is evident. They form in the heavy rainfall area, and develop into meso-α-scale frontal depressions during propagation along the frontal zone, where the significant baroclinicity is seen within the nearly moist neutral layer in the lower troposphere.
An eigen analysis of the simple air-sea coupled model is carried out to understand the coupled mechanism with the slow time scale (so called ‘slow mode’) related to the zonal phase difference between the SST and atmospheric heating anomalies. Both frequency and instability of the slow mode are very sensitive to the zonal phase difference between the SST and atmospheric heating anomalies. When the positive atmospheric heating is located between one-quarter wavelength west and one-quarter wavelength east of the positive SST anomaly, the slow mode becomes the unstable eastward-propagating mode. The further eastward shifting of the atmospheric heating results in damping of the eastward-propagating mode resembling the forced Kelvin mode. On the other hand, the slow mode becomes the unstable westward-propagating mode when atmospheric heating lies farther west than one-quarter wavelength west from the SST anomaly. This unstable westward-propagating mode resembles the forced Rossby mode. SST changes in the eastward- and westward-propagating slow modes are mainly induced by the changes of the oceanic height and the zonal advection by the current, respectively. The slow mode in the fast-wave limit and the non-rotating system is also discussed.
The authors argue that certain aspects of the rotational, synoptic-scale disturbances of the wind field that are observed in ITCZ or monsoon trough regions can be understood by considering the linear response of a dry, initially resting atmosphere to a pulse of heating whose amplitude and spatial and temporal scales are characteristic of a large mesoscale convective system. The key points are that short Rossby waves have small intrinsic group and phase velocities, and that a heating pulse projects much more energy on the Rossby modes if it is located slightly off rather than on the equator. It follows that synoptic-scale Rossby waves, with characteristics broadly similar to those of observed disturbances, should be present in off-equatorial regions of persistent deep convection, since large mesoscale convective systems tend to develop in such regions.
In this study, precipitable water is estimated from GPS data with high time resolution at Lhasa. Mean precipitable water in the premonsoon and the monsoon periods are about 10mm and 25mm, respectively, while precipitable water increases in short term at around the onset. Prominent diurnal variation of precipitable water can be observed in both periods. The minima of the diurnal variation appear around 1800 LST and 1500 LST in the premonsoon and the monsoon periods, respectively. These characteristics indicate that the diurnal variation of water vapor is strongly affected by the local circulation over the deep valley.
The stability of convection between the day and night sides on the sphere is examined for the case including the dynamical effect of planetary rotation (the Coriolis force). First, nonlinear solutions representing convection between the day and night sides are numerically obtained for various parameter values. For some solutions, the convective motion is restricted to the equatorial region by the equatorial β-effect. The linear analysis shows that all the convection cells are stable in the parameter range examined in this study.
Folland and Parker (1995) proposed the correction (so-called bucket correction) to historical sea surface temperature (SST) data from ship reports such as the Comprehensive Ocean-Atmosphere Data Set (COADS). In order to examine the validation of this correction, comparison is made between SST data and long-term coastal SST (CSST) data taken at nine stations around Japan. For this purpose, we extract SST data in the adjacent areas surrounding nine CSST stations, from the files of COADS and the Kobe Collection data which have been recently released by the Japan Meteorological Agency and the Japan Weather Association. As a result, it is found that the data of five CSST stations among nine stations are suitable for comparison. When Folland and Parker's correction is adopted to the historical SST data, the systematic biases in monthly mean SST anomalies have been corrected almost perfectly at three stations, and the biases at the other two stations have been reduced by 40-50%.