Based on long-time observational datasets, the inter-decadal variations of East Asian summer monsoon (EASM) and summer precipitations over North China together with the relationship between them are investigated by using composite analysis and wavelet transform. Results show that both EASM and summer precipitations over North China have undergone considerable inter-decadal variations over the last 100 years. The Inter-decadal variation of EASM is characterized by four major strong-weak phases, including two strong EASM periods, that is, the period of 1900~1910 and that from the late 1930s to end of 1960s, as well as two weak EASM periods from late 1910s to the end of 1930s and after 1970s. Corresponding to the inter-decadal variation of EASM, three evident abrupt changes have taken place in 1905, 1948 and 1971 respectively. It has been found that the atmospheric anomalous patterns for strong EASM years are completely distinct from that in weak EASM periods. The inter-decadal variability has been found in the summer precipitations over North China as well. Summer precipitations in North China have gone through four major dry-damp periods, and richer (less) rain periods are in good agreements with strong (weak) EASM periods on inter-decadal scale. Further investigations suggest that summer precipitation anomalies over North China are closely related to the variations of EASM on inter-decadal scale. During stronger (weaker) EASM periods, summer SLP and 500hPa geopotential height both exhibit negative (positive) anomalies over East Asia, implying Indian Low deepens and West Pacific Subtropical High (WSPH) is north (south) than normal. As a result, the North China summer precipitation is richer (less). It is noted that the relationship between precipitation and EASM is changeable with time and also shows inter-decadal features.

By using observational data, we studied the relationship of the interannual variation of sea surface temperature anomalies (SSTA) between tropical Indian and Pacific Oceans. The empirical orthogonal function (EOF) analyses of SSTA showed that the dominant modes in tropical Indian Ocean are the unipole mode with same SSTA sign in basin-scale and the dipole mode with a reversal in sign across the basin, respectively. The dominant mode in tropical Pacific Ocean is the El Nino mode. All unipole, dipole and El Nino modes display noticeable interannual variations. The wavelet squared coherency analyses showed that in the interannual time-scale, the SSTA in NINO3 region (150°W- 90°W, 5°S-5°N) in tropical eastern Pacific is closely related with the unipole and dipole modes in the tropical Indian Ocean. It is found that the El Nino lags the dipole mode and precedes the unipole mode. The El Nino from its developing phase to the decaying phase corresponds to SSTA in the tropical Indian Ocean varying from the dipole mode to the unipole mode. The physical connection of El Nino with dipole and unipole modes is also discussed. It is found that variations of the zonal wind anomalies over both tropical Indian and Pacific Oceans are affected greatly by the convection over the area in the eastern tropical Indian Ocean and western tropical Pacific. The variation of the convection accompanied with the evolution of El Nino alters the zonal winds and hence associated oceanic processes, which are responsible for SSTA in tropical Indian Ocean changing from the dipole to unipole mode.

The high quality dataset from the South China Sea (SCS) Monsoon Experiment and 40-year NCEP/NCAR reanalysis data are used to investigate the large scale features and abrupt change in meteorological elements during the onset of the SCS summer monsoon. It is found that the SCS summer monsoon establishment is characterized by the South Asian High migrating swiftly from the eastern side of Philippines to the northern part of Indo-China Peninsula and the enhancement of the Bay of Bengal trough and equatorial westerly over the Indian Ocean associated with the equatorial westerly expanding towards northeastward, and followed by the mid-low latitude interaction and continuous retreat eastward of the western Pacific subtropical high. Numerical results reveal that the Indial Peninsula acts as a critical role for the enhancement of the Bay of Bengal trough with a cyclonic difference circulation excited to the east side of the peninsula through ground sensible heating in such a way that the SCS summer monsoon occurs prior to the Indian summer monsoon.

The analysis of ERS-1,2 SAR data of the Bering Strait, obtained in summer 1995, 1998 and 2000 has allowed to observe many important oceanic processes. They include meandering fronts and vortex activity (well pronounced in the eastern part of the Strait), strong jet current at the Prince Wales Cape, intrusions of the cold Chukchi Sea water (extensions of the Siberian Coastal Current) in the western part of the Strait. These images demonstrate some interesting diversions from the northward current typical for the Bering Strait. The flow direction in the central part of the Bering Strait can be revealed from prominent wake features. Also, generation of internal waves on fronts can be detected in some images. Especially impressive is the large variety of surface manifestations of vortex streets north of the Fairway Rock due to high variability of the incident flow. The asymmetry of the Rock causes a special form of the Karman vortex street consisting of a row of single vortices. Specific arc-like features resembling internal wave manifestations can be observed in ERS-SAR images, obtained in the Bering Strait and surrounding waters. Two possible reasons of such features - meander of low salinity water or/and interaction of tidal currents with the bottom relief are discussed.

Convectively coupled, tropical low-frequency distrubances are examined by means of eigenanalysis to the linear dynamical operator based on a T21 multilevel primitive model that involves cumulus convetions and surface heat fluxes. With relevant dissipation terms and an adjustment scheme employed to parameterize the convections, no unstable mode emerges while some of the eigenmodes show decay timescale longer than the intrinsic dissipative timescale. Under the zonally unfiorm basic state, one of these less damped modes has a zonal wavenumber 1 structure with the period of 34dy, which may be considered as a prototype of the Madden-Julian Oscillation (MJO). While a forced Kelvin wave prevails on the equator in this mode, frictional convergence in the boundary layer to the east of heating appears crucial in generating the successive convective heating anomally hence slow eastward propagation of the mode. When we incorporate an idealized Walker circulation into the basic state, a similar mode is obtained with longer period and decay timescale but the structure localized over the Indian Ocean to the western Pacific. It is noteworthy that, however, the 2nd MJ mode is traced back, in the eigenspectrum, to a zonally uniform least damped mode but not to the 1st MJ mode identified under the zonal mean basic state. These results may indicate that the origin of the observed MJO resides in a zonally uniform convective mode which is modified by interacting with the mean Walker circulation, but not in zonal wavenumber 1 modes which have been discusssed in previous studies.

The secondary circulation of the southern hemispheric polar vortex diagnosed from objective analysis is compared wtih those estimated from minor constituent observation data by Halogen Occultation Experiment and by Improved Limb Atmospheric Spectrometer (ILAS). The secondary circulation driven by wave-mean-flow interactions plays an important role in the formation and maintenance of polar vortex. We are developing a diagnostic tool of the Lagrangian-mean circulation and wave-mean-flow interactions for the zonal mean states based on the pressure-isentrope hybrid vertical coordinate. Using this tool, we depict the secondary circulation from NCEP/NCAR reanalysis. The zonal mean vertical velocity is downward in the inner region of the polar vortex, while it is almost zero near the edge of the polar vortex. This is qualitatively consistent with the vertical displacement of material surface estimated from the ILAS data of minor constituents. In the mature stage, to our diagnosis, the outer region of polar vortex becomes a major downward branch of the Brewer-Dobson circulation. This must be validated with satellite observation in the future.

Equatorial upwelling in the eastern equatorial Pacific Ocean generates relatively cold temperatures and high iron concentrations in the surface ocean layer. The abundance of iron increases biological productivity in the eastern equatorial Pacific and leads to phytoplankton blooms, which in turn may affect the mixed-layer temperatures by an enhanced near-surface absorption of solar light. Here we use a simplified atmosphere-ocean model for the tropical Pacific to quantify the effect of ocean biology on tropical surface temperatures. It is shown that moderate phytoplankton blooms, occuring e.g. during La Nina conditions, lead to a vertical redistribution of heat in the surface layers of the eastern equatorial Pacific and an associated surface layer warming of about 20 W/m². The positive air-sea coupling in the eastern equatorial Pacific plays an important role in amplifying this signal, thereby damping La Nina conditions. This temperature-regulating feedback acts as a biological thermostat within the surface ocean and influences also the amplitude and asymmetry of the El Nino-Southern Oscillation.

The Arabian Sea surface chlorophyll data derived from the Sea Wifs sensor during the post ENSO (1997-98) months analyzed with reference to its corresponding monthly climatic data. The monthly color response computed through differentiation and normalization with reference to its climatic value and represented in percentages. The trends observed in inter and intra-annual mode for the months of 1998 to 2000 analyzed in relation to similar observation made with sea surface temperature (SST) over the area. Analysis also carried out in relation with the changes in weather and climate over the area and the prevailing oceanic processes. The color response indicated about 30% change in surface chlorophyll over the period. The lower concetraiton of sruface chlorophyll observed in 1998 increased from 40% in 1999 to 60% in 2000, respectively. The annual change observed in ocean color response was about 23.7% in 1999 and 3.4% in 200 over their previous years. The average annual change in surface chlorophyll over the period 1998-2000 was about 11.32%, while peak rates of monthly change recorded to an extent of -38.6% in April 1998 to a maximum value in 40.07% in February 1999. Similar responses also observed in the SST of the area. The thermal response observed in the Arabian Sea was compared with those in the central and the eastern Pacific Ocean. These changes were attributed to the changes in ocean and atmospheric processes during summer and winter months, including that of 1997-98 ENSO phenomena.

Satellite sensor designs, data assimilation and retrievals of geophysical parameters all require a fast and accurate radiative transfer model. In general, Stokes vector can be derived from the differential and integral radiative transfer equation. The discrete ordinate method was developed to approximate the integral term so that the equation is linearized to a set of the ordinary differential equations that are then solved from the eigenvalue method. In this study, we further derives the radiance gradient (Jacobian) for a scattering and emission atmosphere, which is a crucial component in satellite data assimilation. In addition, we also review land and ocean surface emissivity models affecting both the forward and adjoint computations.

The satellite data for June-July 1997 at the Southern Great Plains site of the Atmospheric Radiation Measurement program are analyzed. The observed clouds are classified into high, midlevel and low clouds according to their top heights. For each cloud type, the contribution to the total fractional cloud cover from clouds of different sizes is determined using a Lagrangian cloud classification scheme. It is found that in the midlatitude continental, convectively active environment, more than half of the total cloud cover is from high clouds, of which 80% comes from clouds with area > 4 × 10⁴ km². For midlevel clouds, more than 50% of the contribution to cloud cover is from small clouds (e.g. cloud area < 4 x 10⁴km²).. Almost all of the low clouds with significant contribution to cloud cover have spatial scales <4 × 10⁴km². This suggests that most of the midlevel and low clouds are of subgrid scale to a typical GCM resolution. We further found that cloud radiative properties, such as cloud albedo, outgoing longwave radiation and cloud radiative forcing, have strong scale dependence. Bigger clouds are brighter and have lower OLR. These results indicate that contributions to the observed cloud radiative forcing are dominated by large cloud systems.

During the Indoex experiment, a specific effort was done in LMD, France, for collecting the satellite data relevant to the region and period, and put them in a well conditioned data base. Meteosat-5 was moved by EUMETSAT over the Indian Ocean, and is the leading satellite for the studies presented here. METEOSAT allows the study and tracking of the convective systems and events, as well as estimation of the upper tropospheric humidity. Other satellite information on the water vapour in the atmosphere or precipitation come from microwave instruments as SSM/I or the instruments of TRMM. Concerning the radiative budget components, ScaRaB on the Russian satellite RESURS was providing outgoing radiative fluxes. All this information is combined here in order to study the fluctuations of convection at different time space scales and its relationship to environmental conditions such as humidity, sea surface temperature,...

A new generation of research aircraft, based on modern mid-sized business jets, will provide access to upper regions of the atmosphere and remote regions of the planet not reachable by the current research aircraft. Equipped with extensive research modifications, modern instruments, and advanced air-to-ground communication systems, these new aircraft will allow investigators to attack key questions in global atmospheric dynamics, global cycles of water and carbon, global energy budgets, and regional and global air quality and chemical transport. A three-aircraft fleet of these aircraft could provide unprecedented coordinated intercalibrated coverage of the planetary atmosphere and surfaces in a manner that greatly enhances the total ground, ocean, and satellite observing system.

Three methods of analyzing Stratospheric Aerosol and Gas Experiment (SAGE) II tropospheric aerosol extinction data are described and intercompared in terms of global maps and vertical contour plots of the extinction coefficient, or its equivalent. The first method, which has been in use for several years, is found to be biased toward smaller aerosols (effective radius < about 0.25 μm), while the second more recently developed method characterizes the distribution of larger aerosols (effective radius > 0.25 μm). The third method which, unlike the first two methods, is capable of producing an altitude resolved aerosol climatology down to about 1 km above the earth's surface, requires an assumption about the amount of cloud contamination in the data set. Given the correctness of this assumption, the method is able to derive the total extinction due to both large and small aerosols. Aerosol climatologies produced by all three methods are shown and intercompared, with particular emphasis on the lofting of dust from Asian and other Northern Hemisphere deserts and its subsequent advection over the western Pacific Ocean.

Due to the significant climatic effects of snow cover, it is very important to improve numerical simulation of snow cover in climate models. With the field data from Col de Porte, Freance and BOREAS, the evolution of seasonal snow cover is simulated with Compreshensive Land Surface Model. The objective of this study is to validate the model and investigate the snow cover proceses in both the alpine regions and the boreal forest. The sensitivity of the simulated results to some model parameters and the different phsyics responsible for the snow cover variation in vegetated and non-vegetated cases are investigated. The modeling results are in good agreements with the observational, and the model represents the snow-pack development and both the timing and the rate of seasonal snowmelt accurately in both cases, indicating that the model has the capacibilty to capture the main features of seasonal snow cover under water holding capacity have significant effects on the simulation of snow cover. The physical processes related to the snow cover variaiotn are different whether vegetation exits or not. Vegetation plays an important role in the dynamics of seasonal snow cover by controlling the radiative fluxes at the snow surface and thus the surface energy balance.

Results of microwave sounding of ocean surface are discussed. The study is based upon the data from airborne two-polarisation side-looking Ku-band radar, satellite based ERS SAR and the 'ALMAZ' SAR. The paper is dedicated to the theory and practice of analysis of radar images of sea surface, obtained under unstable atmosphere, when ocean is warmer than near-surface air. In this case, the sea surface reveals wind field variations in the MABL caused by atmospheric convective processes, accompanied by air motions with mainly vertical direction. Changes in radar manifestations of convection signatures are connected with the degree of thermodynamic instability of the atmosphere. It is shown that radar images of ocean under unstable atmosphere provide the imprints of convective processes in forms prescribed by theory, but in natural conditions air circulation in cylinder- or cell-formed structures differs from the model ones. It is suggested that the detection and investigation of active ocean-atmosphere energy exchange should be based on the polarization differences of radar cross section, especially under low grazing angles. The 2D-correlation functions of VV and HH-polarized radar images are considered with the aim to establish a quantitative criterion for the identification and discrimination between stable, unstable and neutral ocean-atmosphere stratifications.

Global radiosonde data are required by meteorological analysis centers for initializing numerical prediction models for weather forecasting, and represent an increasingly valuable resource for studies of climate change and in the development, calibration and validation of retrieval techniques for atmospheric temperature and water vapor profiles from satellite. Unfortunately, the usefulness of radiosonde data is limited by sensor accuracy, by data reporting practices, and by the fact that sonde and sensor types vary by location and with time. Numerous studies and reports have called for a reference sonde to serve as a transfer standard to compare and connect data from past, present and future sonde systems. We are working on developing a reference radiosonde system at the Atmospheric Technology Division (ATD) at NCAR. The reference radiosonde system will carry the best sensors, have a flexible infrastructure to host multiple and different user-provided sensors and will be recoverable to reduce costs. The first version of the reference radiosonde system was deployed in the Oklahoma panhandle and Dodge City, KS (NWS radiosonde site) during the International H2O Project (IHOP_2002). A total of sixteen reference sondes were launched during IHOP either with Vaisala RS80 or Sippican (VIZ) radiosondes. The humidity data from the reference humidity sensor (Snow White, SW) are compared with Vaisala and VIZ data. The comparisons show that (a) VIZ carbon hygristor fails to respond to humidity changes in the upper troposphere, (b) the carbon hygristor inside the reference sonde has slower response than that inside NWS VIZ sonde, (c) Vaisala RS80-H agrees with SW very well in the middle and lower troposphere, and (d) SW can detect cirrus clouds near the tropopause and possibly estimate their ice water content (IWC). The climate impacts of these results are also discussed.

A remarkable meso-scale anticyclonic vortex pair in the northern part of the South China Sea (SCS) from later August to early September 1994 is documented by the in situ observation data. Their spatial structures were examined in detail from the horizontal and two nearly perpendicular vertical angles of view. The horizontal scales of these two vortices were around 100 km, 50 km, and their vertical scales were about 500 m, 1000 m, respectively. Two 'warm core'structures associated with these two vortices were found in their horizontal and vertical analyses. The closer spacing of these two vortices (namely 60 km), which was smaller than the Rossby radius of deformation, suggested that they might merge with each other during their next evolutionary stages and form into a larger vortex eventually.

The dynamic and random processes of ocean features and their multi-element mixs make the detections of ocean phenomena and information seperations so much complicated. The multi-parameter synthetic aperture radar (SAR), including multi-frequencies, multi-polarizations, multi-incident angles multi-resolutions and multi-swaths etc., are quite significant approaches in order to obtain a lot of oceanic multi-elements and the parameter estimations of these elementss according to SAR images. In the paper, the complication of the ocean processes and their application needs as well as multi-parameter SAR remote sensing abilities are briefly introduced at the first. The remote sensing principles and methodologies of multi-parameter SAR studying on complicated oceanic dynamic features are described. Multi-parameter SAR simulations and detections of sea surface waves, internal waves, currents and sea surface winds etc. are studied in detail. The further development of multi-parameter SAR systems and their potential in ocean applications is discussed and concluded at the final.

Analysis of log-amplitude scintillation due to troposphere clear-air turbulent and meteorological parameters variation is shown at microwaves (MW) on slant paths, based on ITU-R turbulence atmosphere structure parameter, temperature and relative humidity along vertical path. Comparisons of Karasawa model based on the data obtained from a low-elevation microwave propagation experiment and ITU-R Recommendation model prediction results with evaluation results are shown and discussed. The results show that although the relative humidity effected on optical refractive index of a cell is not principally element at optical wave band, at microwave and millimeter-wave band, the relative humidity and temperature is the major factor impacted on log-amplitude scintillation. Hence, the variations of temperature and relative humidity with height, which can be obtained by experiment (or test) and weather observation method is important for low-elevation satellite communication and microwave remote sensing. A atmosphere structure constant C_n² model, which varies with height, is presented based on ITU-R and Karasawa amplitude scintillation model, existing ITU-R C_n² model for optical and meteorologic measured relative humidity and temperature data, at 10~30GHz. In this C_n² model it is considered that relative humidity and temperature varies with height. The log-amplitude scintillation deviation calculated in terms of the C_n² model based on humidity and temperature vertical profile compare with values predicted by means of ITU-R and Ortgies model applied to Italsat channels. It is emerged that the calculation results based on the C_n² model agree almost with prediction results by ITU-R and Ortgies model at 10~30GHz and there is an advantage that relative humidity and temperature varied with height has be considered in the C_n² model. Therefore, it is shown that the C_n² model is usable and is more practical.

The Megha-Tropiques satellite is devoted to the study of the atmospheric water cycle in the tropics and its relation to the radiative budget. It is aiming to study both the energy and water budget of the intertropical band and the life cycle of the convective complexes in the Tropics. The orbit of the satellite allows it to sample several times per day the zone from 23°N to 23°S, where most of the precipitation of the planet and large energy exchanges occur. The three instruments of the mission are a microwave imager, a microwave water vapor sounder and a radiative budget instrument. The launch of this mission by an Indian Rocket is foreseen in 2006-2007. It will hopefully coincide with the time frame of the Global Precipitation Mission, allowing to improve its tropical coverage.