Research on Internal Solitary Wave Detection and Analysis Based on Interferometric Imaging Radar Altimeter Onboard the Tiangong-2 Space Laboratory

The Tiangong-2 space laboratory was launched by China on 15 September 2016, carrying the Interferometric Imaging Radar Altimeter (InIRA), the first of the latest generation of imaging altimeters that can perform imaging and acquire elevation information simultaneously. This paper analyzes the feasibility of using InIRA images to obtain two-dimensional characteristics of oceanic internal solitary waves (ISWs) and information about vertical sea surface fluctuations caused by the propagation of ISWs. The results show that InIRA demonstrates a relatively reliable ability to observe ISWs with high resolution and can identify the fine-scale features of ISWs of different forms. Furthermore, InIRA can observe centimeter-level changes in the Sea Surface Height Anomaly (SSHA) caused by ISWs. The geometric relationship between the sensor’s flight direction and the propagation direction of ISWs does not affect its detection effect. However, the swath width of InIRA is too narrow to fully capture ISW information, and the height accuracy of InIRA height product images is not insufficient to detect the height information of small-scale ISWs. These shortcomings need to be considered in the future development of imaging altimeters to increase their potential for detecting mesoscale phenomena in the ocean.

Normalized anomaly patterns of meteorological elements: A case study of Northeast monsoon 2002 and 2004

ekSle foKkfud vk¡dM+ksa dks lkekU;h—r folaxfr;ksa ds laca/k esa crkuk izk;% lgk;d jgrk gS D;ksafd blls lkekU; cuke vlkekU; ekuksa dks igpkuuk ljy gks tkrk gSA blds vykok blls LFkku ds izHkko rFkk vk¡dM+ksa ds izlkj dk izHkko nwj gksrk gS vkSj nks fHkUu LFkkuksa esa izs{k.kksa dh rqyuk lqfo/kktud gks tkrh gSA bl izdkj lkekU;h—r folaxfr ¼,u- ,-½ iSVuZ vFkkZr fu/kkZfjr le; esa folaxfr;ksa dk LFkkfud forj.k izfrdwy ekSle dh ?kVukvksa esa iwokZuqekudrkZvksa ds fy, ,d l’kDr midj.k cu tkrk gSA bl 'kks/k i= esa mRrjiwohZ ekWulwu 2002 dh varj&ekSleh fof’k"V iz—fr ij fopkj djrs gq, ekSle dh izfrdwy ?kVukvksa dk fo’ys"k.k djus ds fy, ,u- ,- iSVuZ ds mi;ksx ij dk;Z fd;k x;k gSA mRrj iwohZ ekWulwu 2002 ds nkSjku lw[ks tSlh fLFkfr;ksa ds ckjs esa foLrkj ls ppkZ dh xbZ gS vkSj muds dkj.kksa dh tk¡p dh xbZ gSA ;g Hkh ns[kk x;k gS fd mRrj iwohZ ekWulwu 2002 ds varj ekSleh iz—fr iSVuZ esa izsf{kr lw[ks tSls fLFkfr dk ,d dkj.k 200 ,p- ih- ,- Åijh ry fjt dk gksuk vFkok ldkjkRed HkwfoHko Å¡pkbZ folaxfr] uoEcj esa lkbcsfj;u gkbZ esa udkjkRed ek/; leqnz Lrj nkc folaxfr] 200 ,p- ih- ,- iou folaxfr dh rhozrk gks ldrk gSA fuEu es?k ek=k] 'kq"d cYc rkieku vkSj lkis{k vknzZrk ls mRrj iwohZ ekWulwu 2002 esa lw[ks tSlh fLFkfr;ksa dk irk pyk tcfd vkSlr iou xfr ds ,u- ,- ls caxky dh [kkM+h esa pØokrksa ds {kh.k gksus vkSj izk;}hih; Hkkjr rd ugha igq¡pus ds ckjs esa irk pykA mRrj iwohZ ekWulwu 2004 ds fy, fuEu es?k ek=k] lkis{k vknzZrk] 'kq"d cYc rkieku rFkk vkSlr iou xfr ds ,u- ,- iSVuZ ls mRrj iwohZ ekWulwu 2002 ds ekeys esa bu ekSle foKkfud izkpyksa ds fy, ,u- ,- iSVuZ esa lw[ks tSls fLFkfr;ksa ds izs{k.kksa dh iqf"V gqbZA It is often helpful to express the meteorological data in terms of normalized anomalies as they make it easier to discern normal versus unusual values. Also it removes influence of location and spread from data and facilitates the comparison of observations at two different locations. Thus, Normalized Anomaly (NA) patterns i.e., spatial distribution of anomalies at specified time make a powerful tool in hand of forecasters to analyze extreme events. The present study explores the utilization of NA patterns for the purpose of analyzing extreme events by focusing on the inter-seasonal peculiar behavior of Northeast monsoon 2002. A detailed discussion is given and reasons are explored for droughts like situations during Northeast monsoon 2002. It was also noticed that the persistence of 200 hPa upper level ridge or positive geopotential height anomaly, negative mean sea level pressure anomaly over Siberian High during November, strength of 200 hPa wind anomaly can be one of the reasons for drought-like situation observed in the inter-seasonal behavior pattern of Northeast monsoon 2002. NA patterns of low cloud amount, dry bulb temperature and relative humidity captured drought-like situations during Northeast monsoon 2002 while NA of average wind speed captured the scenario of dissipating cyclones in the Bay of Bengal itself and not reaching to Peninsular India. The NA patterns of low cloud amount, relative humidity, dry bulb temperature and average wind speed for Northeast Monsoon 2004 confirm the observations of drought like situations seen in NA patterns for these meteorological parameters in case of Northeast monsoon 2002.

Evaluation of altimetry satellite data products and sea level trends in the Indonesian maritime continent

This study examines the accuracy of the sea surface height anomaly (SSHA) altimetry data products of Copernicus, Colorado University (CU), and X-TRACK-Centre for Topographic studies of the Ocean and Hydrosphere (X-TRACk-CTOH). The SSHA derived from altimetry accuracy was tested by comparison with tide gauge (TG) observations. Taking measurements along the IMC coast demonstrates the excellent agreement between the SSHA derived from altimetry and the TG observations, with an average root mean square deviation (RMSD) as low as 10 cm and a strong correlation. The study’s findings revealed that the Copernicus data products could be used to monitor sea-level variability and trends in the IMC accurately. The 25-year time series data from SSHA demonstrated that the sea-level trend in the IMC is higher than the global trend.

Evolution of Warm Season Intense Rainfall in Yaan Against a Cold-Anomaly Background

This study investigates the rainfall characteristics during intense rainfall over Yaan against a cold-anomaly background, aiming to refine the understanding of different kinds of rainfall events across complex terrain. Hourly rain gauge records, ERA5 reanalysis data and the black body temperature of cloud tops derived from FY-2E were used. The results show that against a cold-anomaly background, the regional rainfall events (RREs) in Yaan exhibit west-to-east propagation, which is different from the north-to-south evolution of warm RREs. The middle and upper troposphere is dominated by a negative geopotential height anomaly corresponding to the cold anomaly. The cyclonic circulation at the higher level associated with the negative geopotential height anomaly bends the high-level jet to the south, forming a divergent zone over the Tibetan Plateau (TP) and guiding mid-level systems to move eastward. The cyclonic circulation at the mid-level produces a wind shear zone over the TP, generating anomalous vorticity that continuously moves eastward and develops to influence the rainfall over Yaan. The cold Yaan RREs are closely related to the TP low-pressure systems (both vortex and shearline). The anomalous vorticity over the TP can influence the local vortex over the eastern periphery of the TP at a distance mainly by the horizontal advection of anomalous vorticity by the mean flow and then enhance the local vortex mainly by anomalous convergence when it moves near Yaan.

The Quasi-Biweekly Oscillation of Summer Rainfall in Southern China and Its Relationship With the Geopotential Height Anomaly Over the North Atlantic Ocean

Summer precipitation in East Asia has significant quasi-biweekly (10–30-day) oscillation characteristics. By using gauge-based precipitation and ERA-Interim reanalysis data, the basic mode of the quasi-biweekly oscillation of summer precipitation in East Asia and the related circulation from 1979 to 2012 were analyzed. It was found that the middle and lower reaches of the Yangtze River and its south in China were among the key areas for the 10- to 30-day oscillation of summer precipitation. After selecting typical summer precipitation events with 10- to 30-day oscillation characteristics in key areas and conducting composite analysis, it is found that in the dry (wet) phase of quasi-biweekly precipitation in southern China, it is controlled by quasi-biweekly anticyclone (cyclone) at 500 hPa above the key area. During the evolution of quasi-biweekly precipitation, the ridge of the Northwest Pacific Subtropical High is located between 20 and 22°N latitude, and there is no significant variability in the large-scale background circulation. Furthermore, composite analysis of the precursory signal at 500 hPa during quasi-biweekly precipitation in southern China found that there was an obvious quasi-biweekly geopotential height anomaly over the North Atlantic Ocean almost 30 days before the peak day of quasi-biweekly precipitation. While the quasi-biweekly geopotential height anomaly at 500 hPa in the North Atlantic propagates eastward, it also leads the cold air to transport southward. Cold air from high latitudes and warm air from low latitudes converge in southern China, which affects the quasi-biweekly oscillation of precipitation. Hysteresis synthesis of precipitation based on 500 hPa geopotential height’s quasi-biweekly oscillation events over the North Atlantic Ocean comes to almost the same conclusion. Therefore, the 500 hPa geopotential height quasi-biweekly anomaly in the North Atlantic may have important prediction significance for an extended-range forecast of summer rainfall in China.

The Combined Effects of ENSO and Solar Activity on Mid-Winter Precipitation Anomalies Over Southern China

Both the El Niño-Southern Oscillation (ENSO) and the 11-years solar cycle had been identified as important factors that may influence the wintertime southern China precipitation (SCP). However, the interactions between these two factors remain less noticed. In this study, the combined effects of the ENSO and the solar activity on mid-winter (January) SCP are investigated using observational and reanalysis data. Results suggest that both the ENSO and the solar activity are positively correlated with the SCP, although exhibiting distinct spatial patterns. Under different combinations of the ENSO and solar phases, the SCP anomalies show superposition of these two factors to some extent. Generally, the ENSO-related SCP anomalies tend to be enhanced (disturbed) when the ENSO and the solar activity are in-phase (out-of-phase). But this solar modulation effect appears more clear and significant under cold ENSO (cENSO) phase rather than under warm ENSO (wENSO) phase. Further analysis suggests, during the wENSO phase, solar influences on the Northern Hemisphere circulation are generally weak with little significance. In contrast, during the cENSO phase, the solar effect resembles the positive phase of the Arctic Oscillation but with an evident zonal asymmetric component. Its manifestation over the Asia-Pacific domain features by negative geopotential height anomaly over the West Asia and positive geopotential height anomaly over the East Asian coast, a pattern that is favorable for the SCP, thus causing a significant solar modulation on the cENSO-related precipitation anomalies. Further, the potential physical causes of solar effects on circulation are also discussed. Our results highlight the importance of considering solar cycle phase when ENSO is used to predict the East Asian winter climate.

Impact of the El Niño type and PDO on the Winter Sub-seasonal North American Zonal Temperature Dipole via the Variability of Positive PNA Events

In recent years, the winter (from December to February, DJF) North American surface air temperature (SAT) anomaly in midlatitudes shows a “warm west/cold east” (WWCE) dipole pattern. To some extent, the winter WWCE dipole can be considered as being a result of the winter mean of sub-seasonal WWCE events. In this paper, the Pacific SST condition linked to the WWCE SAT dipole is investigated. It is found that while the sub-seasonal WWCE dipole is related to the positive Pacific North American (PNA+) pattern, the impact of the PNA+ on the WWCE dipole depends on the El Niño SST type and the phase of Pacific decadal Oscillation (PDO). For a central-Pacific (CP) type El Niño, the positive (negative) height anomaly center of PNA+ is located in the western (eastern) North America to result in an intensified WWCE dipole, though the positive PDO favors the WWCE dipole. In contrast, the WWCE dipole is suppressed under an Eastern-Pacific (EP) type El Niño because the PNA+ anticyclonic anomaly dominates the whole North America. Moreover, the physical cause of why the El Niño type influences PNA+ is further examined. It is found that the type of El Niño can significantly influence the location of PNA+ through changing North Pacific midlatitude westerly winds associated with the Pacific Hadley cell change. For the CP-type El Niño, the eastward migration of PNA+ is suppressed to favor its anticyclonic (cyclonic) anomaly appearing in the west (east) region of North American owing to reduced midlatitude westerly winds. But for the EP-type El Niño, midlatitude westerly wind is intensified to cause the appearance of PNA+ anticyclonic anomaly over the whole North America due to enhanced Hadley cell.

Ocean Response to Tropical Cyclone Seroja at East Nusa Tenggara Waters

Tropical Cyclone (TC) Seroja is a unique tropical cyclone that has significant impacts along its path, such as floods in East Nusa Tenggara and high waves along the southern coast of Indonesia. Research related to ocean responses to tropical cyclones in Indonesia is still limited due to its rarely occurence in Indonesian waters. The responses of the upper ocean to TC Seroja were investigated using multi-satellite remote sensing of sea surface wind (SSW), sea surface temperature (SST), sea surface height anomaly (SSHA), and numerical model of mixed layer depth (MLD) and chlorophyll-a (Chl-a). The SST cooling occurred around the TC Seroja track at 0.5 – 3°C after the storm had passed. During April 3 – 7, 2021, in addition to spatial SST cooling, changes in chlorophyll-a, SSHA, and MLD were also detected. The chlorophyll-a increase to 2.57 mg/m3 and SSHA reached -10 cm. Thus, the MLD was deeper around the eye of the storm during the cyclone and became uniform after the storm passed. These characteristics indicate the upwelling phenomenon induced by the cyclone.

Dynamics of widespread extreme precipitation events and the associated large-scale environment using AMeDAS and JRA-55 data

This study examines disastrous historical precipitation cases that generate extreme precipitation simultaneously over a wide area in Japan (as in July 2018), defined as widespread extreme precipitation events. A statistically significant large-scale environment conducive for widespread extreme precipitation events over western Japan is investigated based on composite analysis. During a widespread precipitation event, a zonally elongated positive anomaly of the column-integrated water vapor extends from East China to western Japan. In the lower troposphere, a dipole of a geopotential height anomaly exists with positive and negative values at the east and west of the precipitation area, respectively. It is found that the negative geopotential anomaly is enhanced over East China at two days before the event and moves toward the precipitating area mainly due to the PV production term by diabatic heating, in analogy of a diabatic Rossby wave. The temporal evolution of the dynamical forced vertical velocity is well in phase with that the PV production term, inferring the importance of the coupling between the dynamical forced motion and diabatic heating. This result provides a physical understanding of the reason why both the background moisture and the baroclinicity are essential in the composited atmospheric fields and another view to the importance of the feedback parameter between the dynamical motion and diabatic heating.