Can the Southern annular mode influence the Korean summer monsoon rainfall?

We demonstrate that a large-scale longitudinally symmetric global phenomenon in the Southern Hemisphere sub-polar region can transmit its influence over a remote local region of the Northern Hemisphere traveling more than 100° of latitudes (from ~70°S to ~40°N). This is illustrated by examining the relationship between the Southern Annular Mode (SAM) and the Korean Monsoon Rainfall (KMR) based on the data period 1983-2013. Results reveal that the May-June SAM (MJSAM) has a significant in-phase relationship with the subsequent KMR. A positive MJSAM is favorable for the summer monsoon rainfall over the Korean peninsula. The impact is relayed through the central Pacific Ocean. When a negative phase of MJSAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that propagates from sub-polar to equatorial latitudes and is associated with the central Pacific warming. The ascending motion over the central Pacific descends over the Korean peninsula during peak-boreal summer resulting in weakening of monsoon rainfall. The opposite features prevail during a positive phase of SAM. Thus, the extreme modes of MJSAM could possibly serve as a predictor for ensuing Korean summer monsoon rainfall.     

Diurnal characteristics of geoelectric fields and their changes associated with the Alxa Zuoqi M_S5.8 earthquake on 15 April 2015(Inner Mongolia)

In China, efforts are being made to monitor geoelectric fields through a large network of stations deployed and managed by the China Earthquake Administration. The diurnal variations in the geoelectric field waveforms were similar in the quiet magnetic periods when K5(generally, K3 indicates a quiet time). The arrival time points of the maxima in the geoelectric field waveforms exhibited differences in local time related to geographic longitude. The amplitude of diurnal variation was several to 16.6 mV/km and decreased with increasing latitude. Further,the amplitude of diurnal variation, which was related to seasonal changes, was larger in summer and autumn than in spring and winter. The periods of diurnal changes during quiet days were 24, 12, 8, 6, 4 hours and several minutes over large areas. Finally, the observed diurnal variations in geoelectric field prior to the Alxa Zuoqi M_S5.8 earthquake on 15 April 2015 were studied, and pronounced changes in the spectral values of the geoelectric fields were found to be associated with the Alxa Zuoqi earthquake in Inner Mongolia.     

A study on the systematic errors of the tropical forecasts: Influence of physical processes

Summary In this paper, an attempt is made to examine the influence of the physical forcings of an atmospheric general circulation model (AGCM) in the reduction of the systematic errors of the tropical forecasts. A number of major modifications in the parameterization of physical processes were carried out in the operational forecasting system of the European Centre for Medium Range Weather Forecasts (ECMWF) during the period 1984–88 largely in an attempt to reduce the conceptual weaknesses in their formulation. A large number of studies (Slingo et al., 1988; Tiedtke et al., 1988; etc) have demonstrated the positive impact on the reduction of tropical forecast errors to various changes in the treatment of physical processes in the ECMWF model.Keeping in view of these facts, the evaluation of the systematic errors of the ECMWF tropical forecasts is carried out for a period prior to the incorporation of major modifications in the parameterization of physical processes (1984) and corresponding period after such major changes are implemented in the operational AGCM of ECMWF (1988). The paper describes a detailed comparison of the tropical forecast errors for summer monsoon seasons (June-August [JJA]) of 1984 and 1988 in order to bring out the impact on tropical simulation of various improvements in the treatment of physical processes.The results demonstrate a dramatic reduction in the systematic errors of the tropical circulation together with an enhancement of the hydrological cycle to a realistic climatological level with the incorporation of major changes in the treatment of physical processes. Similar improvements are also observed in the winter simulation. In spite of major improvements in the simulation of tropical circulation, the nature of the tropical systematic errors of the ECMWF AGCM, however, remains unchanged. Thus, the inference of the study indicates the requirement of a new approach to the problem of parameterization of physical processes particularly, convection, radiation, boundary layer and their interactions for further reduction of the tropical forecast errors.With 14 Figures     

Studies of the atmospheric stability characteristics during the solar eclipse of February 16, 1980

Observations made with a monostatic sodar and from a 120 m instrumented tower have been used to study the variations in the atmospheric boundary layer at Tarapur (19° 50 N, 72° 41 E) during the solar eclipse of February 16, 1980. Atmospheric instability was reduced below normal values during the eclipse but the atmosphere at no time became stable.     

Evaporation over the Arabian Sea during two contrasting monsoons

Summary Monthly mean surface fields of different meteorological parameters and evaporation are studied for the 1979 (poor monsoon) and 1983 (good monsoon) monsoon seasons over the Arabian Sea, in order to understand the role of evaporation on the Indian monsoon rainfall. It is noticed that in general, the sea surface temperatures are higher in 1983 throughout the monsoon season than in 1979 in the Arabian Sea excepting western region. The mean rates of evaporation on a seasonal scale are found to be equal in both years (3.66×10¹⁰ and 3.59×10¹⁰ tons/day in 1979 and 1983, respectively). No coherence is observed between the evaporation and the west coast rainfall within a season. It is also noted that the pressure distribution over the Arabian Sea is even important to advect the moisture towards the west coast of India, through winds.With 10 Figures     

Evaluation of radiative fluxes over the north Indian Ocean

Theoretical and Applied Climatology - Radiative fluxes are a key component of the surface heat budget of the oceans. Yet, observations over oceanic region are sparse due to the complexity of...     

Objective determination of onset,advancement and withdrawal of the summer monsoon using large-scale forecast fields of a global spectral model over India

Summary In this study, a detailed examination on the evolution of summer monsoon onset over southern tip of the Indian peninsula, its advancement and withdrawal over the Indian sub-continent is carried out by utilizing the analysis/forecast fields of a global spectral model for Monsoon-1995. The data base used in this study is derived from the archives of global data assimilation and forecasting system of NCMRWF, India, valid for 00UTC at 1.5° latitude/longitude resolution for the summer monsoon period of 1995. By utilizing the analyses and forecast fields, and the established knowledge of the Indian monsoon, objective criteria are employed in this study for determining the onset, advancement, and withdrawal of the monsoon.It is found that all the major characteristics of Monsoon-1995 are captured well by the analysis-forecast system even though the criteria adopted in this study are more objective and different in nature as compared to the conventional procedures. The onset date of monsoon over the southern tip of the Indian peninsula as determined by the dynamical onset procedure is found to be matching well with the realized date. Further, the evolution of monsoon onset characteristics over the Arabian Sea both in the analyses and forecasts is found to be in good agreement with the earlier studies. However, the magnitudes of net tropospheric moisture build-up and tropospheric temperature increase differ with respect to analyses and corresponding forecast fields. In addition, all important characteristics of the advancement and withdrawal of monsoon over the Indian sub-continent viz. stagnation, revival etc., are brought out reasonably well by the analysis and forecast system.With 10 Figures     

On the Role of the Cross Equatorial Flow on Summer MonsoonRainfall over India using NCEP/NCAR Reanalysis Data

Summary  The role of the cross equatorial flow from the southern Indian Ocean on the Indian Summer monsoon is examined using the National Centre for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) data for the period January 1982 to December 1994. A comparison of NCEP/NCAR data with the satellite data retrieved from the Special Sensor Microwave Imager (SSM/I) sensor onboard the Defense Meteorological Satellite Program (DMSP) exhibited a negative bias for the wind speeds greater than 4 m/s. whereas in the case of specific humidity, SSMI values exhibited a positive bias and the precipitable water derived from the satellite data exhibited a negative bias. The NCEP reanalysis is able to depict the mean annual cycle of both the cross equatorial flow and moisture flow into the Indian subcontinent during the monsoon season, but it fails to depict these differences during excess (1983, 1988, 1994) and deficit monsoon (1982, 1986, 1987) composites. Further, it is seen that inter hemispheric flow far exceeds the excess moisture available over the Arabian Sea indicating that it is the cross equatorial flow which decides the fate of the Indian summer monsoon. Received September 29, 1998 Revised May 20, 1999