Simulation of north India Ocean circulation Using a simple barotropic model and Some sensitivity studies

A non-divergent barotropic model has been formulated on the basis of splitting up method and used to study the circulation in the north Indian Ocean (1-26° N, 4~-99° E). The circulation was simulated for summer and winter seasons separately. It IS found that the model simulated the summer and winter calculation satisfactorily. It is also found that the meridional component of wind stress IS dominant over the zonal component in shaping the Somali current. Some sensitivity studies were also carried out and the results indicate the importance of wind stress curl.

Upper air circulation and thermal anomalies over India and neighbourhood vis-à-vis Indian summer monsoon activity

The three dimensional circulation and thermal anomaly features associated with droughts and floods India are examined using 20 year of upper wind data over India and neighbourhood. The analysis reveals that years of droughts (floods) in India are associated with cyclonic (anticyclonic) circulation anomalies and cold (warm) thermal anomalies in the troposphere between 500 hPa and 200 hPa over northwestern India. In drought years (flood years) upper tropospheric westerly (easterly) anomalies are observed in the lower latitudes in the months of May and June. Tibetan anticyclone shifted to east of its normal position in drought years , during the month of June. The correlation coefficient between the meridional component of the wind at 200 hPa over northwestern India and the summer monsoon rainfall found to be -0.72 which is significant.

Structure and properties of summer monsoon stationary B,"Operational use of Ozone over .southern Asia: an observational study

A study of ten-year (1976-1985) mean July climatology of southern Asia and adjoining ocean areas confirms the presence of a well-defined stationary wave, believed to be due mainly to land-sea thermal contrast over the region, in the fields of several meteorological variables. The wave extends laterally over about 10 degrees of latitude with maximum intensity along about 20° N and vertically from surface to about 300 hPa. Its zonal wavelength is about 2000-2500 km and its amplitude in the field of zonal anomaly of temperature and meridional component of wind is 1 oC and 4ms-l respectively. The trough-ridge system of the wave appears to tilt eastward with height from surface to about 700 hPa and westward aloft up to about 300 hPa, while the warmest-coldest anomaly system appears to tilt eastward all the way from surface to about 300 hPa. A phase difference appears to exist between the geopotential and the temperature fields in both the lower and the upper tropospheres. The aforesaid zonal-vertical tilt of the monsoon trough and phase difference between the geopotential and the temperature fields appears to be compatible, through thermal advection, With a direct conversion of eddy available potential energy into eddy kinetic energy via a west-east (clockwise) overturning with warm air rising in the west and cold air sinking in the east in the case of the eastward-tilting lower-tropospheric trough and an east-west (anti-clockwise) overturning with warm air rising in the east and cold air sinking in the west in the case of the westward-tilting middle and upper-tropospheric trough, An enhancement of the thermal advection and hence the vertical circulation may occasionally lead to development of the trough into a I(JW or depression. However, the question of development of the trough and physical factors, which may contribute to such development, needs to be examined by further study.

The modification of turbulent thermal wind balance by non-traditional effects

The meridional component of the earth's rotation is often neglected in geophysical contexts. This is referred to as the ‘traditional approximation’ and is justified by the typically small vertical velocity and aspect ratio of such problems. Ocean fronts are regions of strong horizontal buoyancy gradient and are associated with strong vertical transport of tracers and nutrients. Given these comparatively large vertical velocities, non-traditional rotation may play a role in governing frontal dynamics. Here the effects of non-traditional rotation on a front in turbulent thermal wind balance are considered using an asymptotic approach. Solutions are presented for a general horizontal buoyancy profile and examined in the simple case of a straight front. Non-traditional effects are found to depend strongly on the direction of the front and may lead to the generation of jets and the modification of the frontal circulation and vertical transport.

Calculation of Deflection of Vertical and Gravity Anomalies Over the South China Sea Derived from ICESat-2 Data

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) satellite uses a synchronized multi-beam photon-counting method to collect data from three pairs of synchronous ground tracks. The sampling rate along the ground tracks is designed to be ∼0.7 m, much smaller than that used in conventional radar altimeters. Hence, it is reasonable to expect an improvement in marine gravity recovery over coastal zones using ICESat-2 data. ICESat-2 provides valid sea surface height (SSH) measurements and a standard data product (ATL12) over ocean areas. This led us to consider the possibility of investigating its ability to calculate the deflection of vertical (DOV) and marine gravity anomalies. We processed ATL12 data about 22 months over the South China Sea (0°–23°N, 103°–120°E) and verified the ability of ICESat-2 SSH measurements to be used in calculating directional components of DOV. The results show that the ICESat-2 SSH data have a similar centimeter-magnitude accuracy level as data from the Jason-2 satellite. Furthermore, the accuracy of cross-track deflection of vertical (CTDOV) calculations between non-identical side beams is lower. For along-track points, the difference in accuracy between the solution of the prime component and the meridional component is significantly reduced, the prime component accuracy is significantly better than the directional components of the gridded deflection of vertical (GDOV), although the enhancement is weak for the meridional component. We also implemented the inversion of the ICESat-2 single mission based on the inverse Vening Meinesz formula, and verified the capability of ICESat-2 gravity field detection using shipborne gravity measurements and XGM2019 gravity field model, and found that the accuracy is 1.35 mGal and 2.47 mGal, respectively. ICESat-2 deserves the attention of the altimetry community, and its advantages are expected to make it an alternative data source for multi-mission fusion inversion of the ocean gravity field in the future.

METEOROLOGICAL ROCKET SOUNDING FOR ATMOSPHERIC RESEARCH AND MONITORING OF GEOPHYSICAL CONDITIONS

The brief description of technical specification of meteorological rockets used at Roshydromet stations, including the exposition of the MERA new meteorological rocket with a lift up to 100 km, MRS 100 rocketsonde, onboard measuring and service equipment, is presented. The technique for measuring atmospheric parameters and the results of investigating long-term variability of temperature and wind in the stratosphere and mesosphere according to long-term (1969-1995) data of meteorological rocket sounding at Volgograd station are considered. It is shown that in the altitude range from 25 to 75 km, trends in temperature and wind speed over Volgograd station for 1969-1995 are nonlinear and, at most altitudes, nonmonotonic. An increase with altitude in the range of trend variations in the analyzed parameters during the surveyed period is discovered: up to 15-19 K in the lower and middle mesosphere for temperature, up to 15 m/s at the stratopause for the zonal component of wind speed, up to 10 m/s in the lower mesosphere for its meridional component.

Validation of wind measurements of two MST radars in northern Sweden and in Antarctica

Two atmospheric VHF radars: ESRAD located near Kiruna in the Swedish Artic and MARA at Indian research station Maitri in Antarctica perform wind measurements in the troposphere and lower stratosphere on a regular basis. We compared horizontal winds at altitudes between about 0.5 km and 14 km derived from the radar data using the full correlation analysis technique with radiosonde observations and models. The comparison with 28 radiosondes launched from January 2017 to August 2019 showed that ESRAD underestimates the zonal and meridional winds by about 8 % and 25 %, respectively. The mean differences between the radar and radiosonde winds are −1.4 m/s and 0.4 m/s. A similar result was found when comparing with the regional NWP model HARMONIE-AROME for the period September 2018–May 2019. The ESRAD random error was estimated to be 2.8 m/s (2.4 m/s) for the zonal (meridional) component. The comparison of MARA with the ECMWF ERA5 reanalysis for January–December 2019 reveals good agreement between them with the mean difference between 0.1 m/s and −0.5 m/s depending on the component and season. The MARA random errors are 2.6 m/s and 2.3 m/s for the zonal and meridional winds, respectively.

Nonlinear MHD Rossby wave interactions and persistent geomagnetic field structures

The geomagnetic field presents several stationary features that are thought to be linked to inhomogeneities at the core–mantle boundary. Particularly important stationary structures of the geomagnetic field are the flux lobes, which appear in pairs in mid- to high mid- to high latitudes. A recently discovered stratified layer at the top of the Earth’s core poses important constraints on the dynamics at this layer and on the interaction of the core dynamics and the base of the mantle. In this article, we introduce the linear and nonlinear theories of magnetic Rossby waves in a thin shell at the top of the Earth’s core. We study the nonlinear interaction of these waves in the presence of prescribed forcings at the base of the mantle of both a thermal and a topographic nature. We show that the combined effects of forcing and nonlinear interaction can lead the wave phases to be locked around a particular geographical longitude, generating a quasi- stationary flow pattern with a significant meridional component. The solutions of the system are shown to be analogous to atmospheric blocking phenomena. Therefore, we argue that persistent and long-lived structures of the geomagnetic field, such as the geomagnetic lobes, might be associated with a blocking at the top of the Earth’s core due to nonlinear stationary waves.

Variability of the lunar semidiurnal tidal amplitudes in the ionosphere over Brazil

The variability in the amplitudes of the lunar semidiurnal tide was investigated using maps of Total Electron Content over Brazil from January 2011 to December 2014. Long period variability showed that the annual variation is always present in all investigated magnetic latitudes and it represents the main component of the temporal variability. Semiannual and intra-seasonal (~ 120 days) oscillations were the second and third components, respectively, but they presented significant temporal and spatial variation without a well-defined pattern. Among the short period oscillations in the amplitude of the lunar tide, the most pronounced ones were concentrated between 7–11 days. These oscillations were stronger around the equinoxes, in special between September and November in almost all latitudes. In some years, as in 2013 and 2014, for instance, they appeared with large power spectral density in the winter hemisphere. There was also observed evidence of antisymetry in the amplitudes maxima and minima of the 7–11 days oscillation with respect to the magnetic equator. These characteristics are compatible with normal mode westward propagating quasi 10 days planetary wave with horizontal wavenumber equal to 1. Besides, using data from a meteor radar located at low latitudes in Brazil for November 2013, when the amplitude of the 7–11 days oscillation was strong, it was possible to identify the presence of quasi 10 days oscillation in the both zonal and meridional component of the horizontal winds. These results suggest a possible coupling process by modulation of the lunar semidiurnal tidal amplitudes that allows the propagation of the 7–11 days waves into the thermosphere-ionosphere system.

PENGARUH MADDEN-JULIAN OSCILLATION TERHADAP DISTRIBUSI TEMPORAL DAN PROPAGASI HUJAN BERDASARKAN PENGAMATAN RADAR CUACA (Studi Kasus : Intensive Observation Period 2016 di Wilayah Jakarta dan Sekitarnya)

IntisariDistribusi temporal dan propagasi hujan selama Intensive Observation Period 2016 (IOP 2016, 18 Januari – 16 Februari 2016) di wilayah Jakarta dan sekitarnya dianalisis berdasarkan rataan longitudinal dan latitudinal data Constant Altitude Plan Position Indicator (CAPPI) radar cuaca, pada periode sebelum, saat dan sesudah fase aktif Madden-Julian Oscillation (MJO). Hasil analisis menunjukkan bahwa distribusi temporal hujan berkurang secara signifikan pada periode MJO aktif dan sesudah MJO, terutama pada dini hari. Di sisi lain, intensitas hujan semakin meningkat dengan nilai rata-rata di atas 30 mm/jam pada periode setelah MJO. Pada komponen zonal, arah propagasi hujan umumnya dominan dari barat ke timur pada ketiga periode analisis, sedangkan untuk komponen meridional, terdapat variasi yang cukup signifikan pada periode saat dan setelah MJO aktif . Pergerakan hujan dari selatan ke utara pada kedua periode tersebut menunjukkan pengaruh siklus diurnal yang semakin kuat dibandingkan pengaruh monsun, setelah MJO melintasi wilayah barat Benua Maritim Indonesia. AbstractTemporal distribution and propagation of rainfall during Intensive Observation Period 2016 campaign (IOP 2016, January 18 – February 16, 2016) in Jakarta and surrounding area were investigated based on the longitudinal dan latitudinal averages of Constant Altitude Plan Position Indicator (CAPPI) dataset of weather radar, during the active Madden-Julian Oscillation (MJO) phase, as well as, pre-MJO and post-MJO periods. The results show a significant decrease of rainfall temporal distribution during the active MJO and post-MJO periods, particularly in the early morning, meanwhile, the rainfall intensity shows significant increase, with the averages of more than 30 mm/hr during the post-MJO period. On the zonal component, the rainfall mostly has eastward propagation for all period while having more significant variations on the meridional component during the active and post-MJO periods. Northward rainfall propagation during the active and post-MJO periods indicates the strengthen effect of diurnal cycle over monsoon after the MJO passed by the western part of Indonesian Maritime Continent.