Entire Analysis Period Research Articles

Investigating the Influence of Carbon Dioxide and the Stratosphere on the Long-Term Tropospheric Temperature Monitoring from HIRS

Abstract Contrary to a midtropospheric warming trend detected from Microwave Sounding Unit (MSU) measurements, High-Resolution Infrared Radiation Sounder (HIRS) temperature (15 μm) channels, sensitive to the thermal emission from the troposphere, produce distinct cooling trends for the period 1980–99. This apparent discrepancy in the tropospheric temperature trend is investigated through radiative transfer simulations using Geophysical Fluid Dynamics Laboratory climate model output and the profiles of the standard model atmospheres. Radiative simulations with time-invariant carbon dioxide concentration throughout the entire analysis period produce trends that are qualitatively similar to that obtained from the MSU observations, implying that the observed cooling trends of the HIRS temperature channels are attributable to increased carbon dioxide concentration over the 20-yr period. Additional simulations with the observed time-varying concentration of carbon dioxide confirm this basic result. Whereas temperature fluctuations dominate variability on monthly to interannual time scales, carbon dioxide changes dominate the decadal trends in both the observations and model simulations. Further simulations examined the sensitivity of the brightness temperature change with respect to the changes in tropospheric and stratospheric temperature. These calculations indicate that the influences of stratospheric temperature on the measured radiances are greater for the HIRS temperature channels relative to the MSU midtropospheric channel. These results highlight the contributions of time-varying carbon dioxide concentrations and stratospheric temperature to the HIRS 15-μm (temperature channel) radiance record and underscore the importance of accurately accounting for these changes when using HIRS measurements for long-term monitoring.

Air–Sea Heat Exchanges Characteristic of a Prominent Midlatitude Oceanic Front in the South Indian Ocean as Simulated in a High-Resolution Coupled GCM

Abstract An integration of a high-resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature (SST) is analyzed to investigate air–sea heat exchanges characteristic of the midlatitude oceanic frontal zone. The focus of this paper is placed on a prominent SST front in the south Indian Ocean, which is collocated with the core of the Southern Hemisphere storm track. Time-mean distribution of sensible heat flux is characterized by a distinct cross-frontal contrast. It is upward and downward on the warmer and cooler flanks, respectively, of the SST front, acting to maintain the sharp gradient of surface air temperature (SAT) that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track. Induced by cross-frontal advection of cold (warm) air associated with migratory atmospheric disturbances, the surface flux is highly variable with intermittent enhancement of the upward (downward) flux predominantly on the warmer (cooler) flank of the front. Indeed, several intermittent events of cold (warm) air advection, whose total duration accounts for only 21% (19%) of the entire analysis period, contribute to as much as 60% (44%) of the total amount of sensible heat flux during the analysis period on the warmer (cooler) flank. This antisymmetric behavior yields the sharp cross-frontal gradient in the time-mean flux. Since the flux intensity is strongly influenced by local magnitude of the SST–SAT difference that tends to increase with the SST gradient, the concentration of the flux variance to the frontal zone and cross-frontal contrasts in the mean and skewness of the flux all become stronger during the spinup of the SST front. Synoptically, the enhanced sensible heat flux near the SST front can restore SAT toward the underlying SST effectively with a time scale of a day, to maintain a frontal SAT gradient against the relaxing effect of atmospheric disturbances. The restoration effect of the differential surface heating at the SST front, augmented by the surface latent heating concentrated on the warm side of the front, represents a key process through which the atmospheric baroclinicity and ultimately the storm track are linked to the underlying ocean.

Comparison of GPCP Monthly and Daily Precipitation Estimates with High-Latitude Gauge Observations

Abstract Monthly and daily products of the Global Precipitation Climatology Project (GPCP) are evaluated through a comparison with Finnish Meteorological Institute (FMI) gauge observations for the period January 1995–December 2007 to assess the quality of the GPCP estimates at high latitudes. At the monthly scale both the final GPCP combination satellite–gauge (SG) product is evaluated, along with the satellite-only multisatellite (MS) product. The GPCP daily product is scaled to sum to the monthly product, so it implicitly contains monthly-scale gauge influence, although it contains no daily gauge information. As expected, the monthly SG product agrees well with the FMI observations because of the inclusion of limited gauge information. Over the entire analysis period the SG estimates are biased low by 6% when the same wind-loss adjustment is applied to the FMI gauges as is used in the SG analysis. The interannual anomaly correlation is about 0.9. The satellite-only MS product has a lesser, but still reasonably good, interannual correlation (∼0.6) while retaining a similar bias due to the use of a climatological bias adjustment. These results indicate the value of using even a few gauges in the analysis and provide an estimate of the correlation error to be expected in the SG analysis over ocean and remote land areas where gauges are absent. The daily GPCP precipitation estimates compare reasonably well at the 1° latitude × 2° longitude scale with the FMI gauge observations in the summer with a correlation of 0.55, but less so in the winter with a correlation of 0.45. Correlations increase somewhat when larger areas and multiday periods are analyzed. The day-to-day occurrence of precipitation is captured fairly well by the GPCP estimates, but the corresponding precipitation event amounts tend to show wide variability. The results of this study indicate that the GPCP monthly and daily fields are useful for meteorological and hydrological studies but that there is significant room for improvement of satellite retrievals and analysis techniques in this region. It is hoped that the research here provides a framework for future high-latitude assessment efforts such as those that will be necessary for the upcoming satellite-based Global Precipitation Measurement (GPM) mission.

The Use of Implanted Programmable Infusion Pumps in the Management of Nonmalignant, Chronic Low-Back Pain

Objectives. To assess the mode-of-use of implanted programmable infusion pumps in patients with nonmalignant, chronic low-back pain. Materials and Methods. Charts from 101 consecutive eligible patients were analyzed retrospectively. Data were extracted relating to patient demographics, pump mode of infusion and flow rate, and medications used. Results. Morphine was the agent most frequently used and most patients received one medication at each visit. At the last visit, 94.1% of patients were receiving constant-flow treatment; 90.1% had received such treatment for≥sixmonths and 68.3% throughout the entire analysis period. For patients attaining constant-flow treatment, mean time from implantation to start of such treatment was 2.7months. Discussion. The results suggest that many patients with nonmalignant low-back pain could be implanted with a constant-flow pump when their programmable device needs replacing or, in some cases, at the start of intrathecal treatment. This would reduce costs and the requirement for surgery.

Demand Elasticity and Benefit Measurement in a Waterway Simulation Model

Waterway simulation models can be used to evaluate system performance and optimize investment and operation decisions, provided the effects of such decisions on demand are properly considered. Some simulation models have considered demand changes due to seasonal variations, economic growth, congestion effects on travel times, and user responses to service interruptions—but not all of these factors together. An elastic demand relationship embedded in a simulation model is used to estimate the effects of changing service times and lock closures during the simulation. Because traffic demand and benefits may be significantly affected by the simulated decisions, evaluation or optimization of the system merely on the basis of total costs is unreasonable. Estimation of the benefits to waterway users also is demonstrated during simulation runs while accounting for the users' responses to lock closures and other factors that affect travel times. Specifically, the present worth of net benefits for the entire analysis period can be computed and used as the objective function for optimization. This approach can account for infrastructure construction and maintenance costs, the effects of service quality and interruptions on user costs, and possible mode shifts in response to waterway service quality.

Surveillance of hazardous materials events in 17 states, 1993-2001: a report from the Hazardous Substances Emergency Events Surveillance (HSEES) system.

Thousands of acute hazardous materials (HazMat) releases occur annually throughout the United States. To prevent human exposure and resulting injuries, it is critical to understand the frequency with which these releases occur, the locations involved, the industries associated, and the specific substances being released. HazMat events data from the Agency for Toxic Substances and Disease Registry's Hazardous Substances Emergency Events Surveillance (HSEES) system were analyzed for frequency and locations of occurrence, major industry categories and sub-categories involved, and substances released. The data analyzed were collected from 17 participating state health departments for 1993 through 2001. During 1993 through 2001, 53,142 HazMat events occurred. Of the 17 states analyzed, Texas had the most releases, comprising 38.3% of all HSEES events. Of the 14 major US Census industry categories analyzed, the manufacturing category had the highest percentage of events (48.7%) followed by transportation, communication, and other public utilities (27.5%). Of the 10 states that participated during the entire analysis period, the numbers of events increased 64.3%. Twelve of 14 major industrial categories experienced increases in numbers of events over the analysis period, while public administration and active duty military events decreased. The substances released most frequently overall included ammonia, sulfur dioxide, and sulfuric acid, respectively. The HSEES data appear to reflect an upward trend in the occurrence of hazardous HazMat events. While it is difficult to definitively conclude whether this trend is due to more events actually occurring or from other factors, reviewing historical HazMat data may help communities, government agencies, and industries prevent or better prepare for potential events in the future.

Evaluation of Portfolio Performance of Turkish Investment Funds

Bu makale A ve B tipi fonlarin 1998 0cak-2000 Haziran donemindeki performanslarini, Sharpe, Treynor, Jensen ve Graham&Harvey kriterlerini kullanarak Hazine bonosu ve IMKB-100 indeksine kiyasla olcumlemeyi amaclamaktadir. Analize 55 A Tipi, 77 B tipi fon dahil edilmistir. Bu kriterlerin fonlari ayni sekilde siralayip siralamadigini gormek icin Spearman dizi korelasyonundan yararlanilmistir. Ikinci olarak, dort farkli yatirim aracinin ortalama Sharp katsayilarinin birbirinden anlamli olcude farkli olup olmadigi Wilcoxon Isaretli Sira testiyle irdelenmistir. Yapilan analizler portfoy performansini degerlendirmede kullanilan dort kriterin fonlari benzer sekilde siraya koydugunu gostermistir. Ama daha onemlisi, gerek tum analiz doneminde gerekse alt donemlerde hazine bonosunun en iyi yatirim araci oldugu, onu sirasiyla IMKB-100 endeksi, B Tipi fon ve A Tipi fonun izledigi gorulmustur. Bu sonuc, fon yoneticilerinin, analiz donemi boyunca, pazar ortalamasindan daha iyi fonlar olusturma cabalarinin yarari konusunda kusku yaratmaktadir.

Population trends of large non‐migratory wild herbivores and livestock in the Masai Mara ecosystem, Kenya, between 1977 and 1997

The total of all non‐migratory wildlife species in the Masai Mara ecosystem has declined by 58% in the last 20 years. This decline ranges from 49% in small brown antelopes to 72% in medium brown antelopes. In individual wildlife species, the decline ranges from 52% in Grant's gazelle to 88% in the warthog. Declines of over 70% have been recorded in buffalo, giraffe, eland and waterbuck. Only elephant, impala and ostrich have not shown any significant decline or increase. Overall, there has not been any significant difference in decline of all wildlife population sizes inside and outside the reserve, except for Thomson's gazelle and warthog. Livestock have not significantly declined over the entire analysis period. However, livestock and cattle populations significantly declined during the 1983–88 period. Donkey declined by 67%, while shoats (goats and sheep) remained stable. In the case of wildlife, land use and vegetation changes, drought effects and poaching are considered to be among the potential factors that may have been responsible for the decline; the decline in livestock during the 1983–84 period was probably due to drought effects.

Leaf photosynthesis and carbon isotope discrimination of cotton in response to potassium deficiency

Leaf photosynthesis and stable carbon isotope composition in response to potassium (K) deficiency was determined with cotton. Cotton plants were grown in sand-filled 8-l pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, Arkansas. Plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting (the fourth true leaf stage) the treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Leaf photosynthesis and related gas exchange measurements were taken 13, 19, and 26 days later. Leaf samples from each analysis date were then dried and reserved for nutrient and carbon isotope analyses. Photosynthesis declined as the K deficiency developed in the no-K treatment. Decreased ∂ A/∂ c i and increased Γ also resulted from declined leaf K concentration, which is attributed to changes in A and respiration in the light. Potassium deficiency also resulted in increased stomatal and non-stomatal limitations to A. Gas exchange studies showed stomatal conductance was most limiting to A at 13 days after treatment establishment (DATE), whereas instantaneous measurements at 19 and 26 DATE indicated non-stomatal conductances were most limiting. However, carbon isotope analyses, which integrated stomatal and non-stomatal conductances over the entire analysis period, indicated that the most limiting resistance to A was stomatal. We conclude from these studies that, during a mild K deficiency, increased stomatal resistance is first to result in a decrease in A and, as the deficiency becomes more acute, biochemical factors also contribute.

Effect of intermediate- and high-purity factor VIII concentrates on immune function in HIV-seropositive haemophiliacs as assessed by quantitative CD 4 counts.

Intermediate-purity factor VIII (FVIII) concentrates are believed to adversely influence cellular immune function and accelerate HIV progression in haemophiliac patients. There are reports that cellular immunity, as measured by serial CD4 lymphocyte counts, is better preserved in HIV-infected haemophiliacs who receive high-purity concentrates compared with those receiving intermediate- or low-purity products. We retrospectively evaluated the rate of CD4 cell count decrease in 44 asymptomatic HIV-seropositive severe haemophilia A patients whose purity of prescribed FVIII concentrate was primarily determined by State of residence. Prior to January 1989 all study subjects received treatment with intermediate- or low-purity products. In January 1989 the patients from Mississippi (n = 15) began to exclusively receive a high-purity, monoclonal antibody purified, plasma-derived product from their State Department of Health. The Mississippi cohort was subsequently converted to a high-purity, recombinant FVIII product in May 1993. Patients from Tennessee and Arkansas (n = 29) received intermediate-purity factor during the entire analysis period. Patients were monitored for an average of 68 months with an average of 11 CD4 cell count measurements. The rate of CD4 cell count decrease was derived from the calculated slope of a simple regression in order to account for large individual CD4 count fluctuations during the study period. There was no statistically significant difference in starting CD4 cell count between the 2 study groups. The rate of CD4 cell count decrease was 21.8 ± 52.9 cells μL(-1) year(-1) and 17.0 ± 32.6 cells μL(-1) year(-1) in the high-purity FVIII group and inter-mediate-purity FVIII group, respectively (P = 0.83). The difference in rate of CD4:CD8 ratio decrease between the two groups was also not statistically significant (P = 0.41). These data suggest that the use of the more costly, high-purity monoclonal antibody purified and recombinant FVIII concentrates does not influence the rate of decrease in CD4 cell count in HIV-seropositive haemophiliacs compared with concentrates of lower specific activity obtained using standard chromatographic techniques.

Analysis of pre-monsoon thunderstorm frequency over Srlniketan, Alipore and Kalaikunda -The possible association with solar activity

ABSTRACT -General characteristic features of thunderstorm frequency (TSF) observed during (1951-89) during pre-monsoon season at Sriniketan (23°39'N, 87"42'E), Alipore (22° 32'N, 88"20'E) and Kalaikunda (21°20'N, 87" 13'E) have been studied. It is seen that premonsoon TSF follows a rough periodicity 0f 6.6) year. For Kalaikunda (KLK) there is an overal1 upward trend and for Sriniketan (SKT) an overall downward trend; whereas, for Alipore (ALP) the trend pattern remains practically constant. The maximum TSF attained by all these three stations is nearly twice that of mean TSF of respective stations.
 The solar influence on the frequency of thunderstorm (TS) has been investigated and found to be interesting. TSF over SKT and KLK attained minimum value while that over ALP was near minimum during 1957; which in turn was the year of maximum sunspot (SS) number over the entire period of analysis. Now in general, if we take SS number and TSF of same year and calculate correlation coefficient (CC) considering all the years. i.e., taking SS without any restriction, the CC comes out to be quite small. But the result is just the reverse when the TSF value of those years is considered when SS number is higher. In particular when SS number exceeds some critical value (~140), TSF decreases sharply.
 The effect of solar sub-cycle, 11-yearcycle and 22-yearcycle un TS has also been discussed. It is seen that during min-max sub-phases, mean TSF is comparatively higher than its value in neighbouring max-min sub-phases and also it is in opposite phase in relation with mean SS. During 11-yearcycle also in most of the cases an opposite phase relationship exists between mean TSF and mean SS.
 

Nevada's Approach to Pavement Management

The Nevada Department of Transportation has a fully implemented pavement management system (PMS) at the network level and an extensive pavement evaluation system at the project level. Both systems use actual field performance data that are collected annually from pavement sections throughout the state. The PMS is being further developed to incorporate performance modeling, life-cycle cost analysis, and network optimization processes. Once fully developed the system will allow the engineer to select the best rehabilitation and maintenance alternative that can carry the pavement over the entire analysis period. The project-level evaluation process includes the use of nondestructive testing data and condition surveys from the PMS. The overall systems are summarized at both levels, and the individual steps that are involved within each system are described.

Nevada's Approach to Pavement Management

The Nevada Department of Transportation has a fully implemented pavement management system (PMS) at the network level and an extensive pavement evaluation system at the project level. Both systems use actual field performance data that are collected annually from pavement sections throughout the state. The PMS is being further developed to incorporate performance modeling, life-cycle cost analysis, and network optimization processes. Once fully developed the system will allow the engineer to select the best rehabilitation and maintenance alternative that can carry the pavement over the entire analysis period. The project-level evaluation process includes the use of nondestructive testing data and condition surveys from the PMS. The overall systems are summarized at both levels, and the individual steps that are involved within each system are described.

Wind Profiler Observations of Tropical Storm Flo at Saipan

Wind profiler and serial sounding observations extending to the upper troposphere are used to analyze Tropical Storm Flo (1990) as it passed within 115 km of the experimental site on Saipan. These data resolve details of the circulation and precipitation structure of the storm and its rainbands. Analysis of principal and secondary rainbands in outer radii indicate that there are considerable similarities with previous studies. Although the bands contained distinct precipitation maxima, there is no evidence of active convection and the mean structure is similar to that observed in the stratiform regions of squall lines. The vertical circulations in the rainbands are weak and complex, but distinct azimuthal wind maxima are observed that have maxima of relative vorticity and inertial stability on the inner edge. The divergence fields for the entire analysis period are strongly coherent and are indicative of vertically propagating gravity waves generated in the near inertially neutral outflow layer. The analysis thus demonstrates the usefulness of wind profilers for tropical cyclone observations.

Tax Reform's Impact on Insurance Industry Stock Returns

This article analyzes the market response of insurers' stock returns to the formulation debate, and enactment of the Tax Reform Act of 1986. Provisions of the Tax Reform Act portended increases in the effective tax rates of insurers despite the proposed lowering of marginal rates. The stock prices of insurers reacted negatively in the formulation, debate, and Committee mark-up phases of the legislative process. Significant abnormal returns were not evidenced in the enactment phase. Several provisions of the Tax Reform Act of 1986 (hereafter referred to as TRA '86) boded unfavorable consequences for insurers. The repeal of the 20 percent special life insurers' deduction, limitations of loss reserves to the present value of unpaid losses, reduction n the deductibility of unearned premiums, taxation of a portion of certain dividends (those subject to the intercorporate exclusion) and previously tax-exempt securities, and the potential tax on inside buildup, were aimed directly at the operations of insurers.(1) Stockholders' expectations could have been adversely impacted by the announcement of any one or combination of these provisions as they progressed through the legislative process. The purpose of this article is to analyze the market response of insurers' stock returns to the formulation, debate, and enactment of TRA '86. Data and Methodology The sample analyzed in this study consists of 19 large, publicly-traded insurers.(2) Each company in the final sample successfully completed the following screening process. First, a sample participant had to have an uninterrupted return series for the entire analysis period. Second, the shares of a sample company had to be actively traded so that non-synchronous price data were not an important problem. Third, a sample participant could have no major firm-specific announcements during the estimation and event intervals. The screening for firm-specific announcements entailed a search of the Wall Street Journal Index beginning six months prior to an event date and extending through the analysis period. When a relevant firm-specific event occurred, the company was eliminated as a sample observation. The well-known Fama, Fisher, Jensen, and Roll methodology is used to estimate the market's reaction to new information about TRA '86.(3) The Fama, et.al. approach facilitates the construction of statistical tests that can reveal significant departures of actual returns from those predicted by the single-index return generating model. Once a sample has been screened for return variations due to specific firm effects, the remaining residual (abnormal) returns are attributable to the event being studied. The event interval analyzed in this article extends from 60 days prior to a particular event date (ED-60) to 60 days after the event date (ED+60). Furthermore, each of the four event windows (EWs) was separated into several sub-phases around its specific event date. The reasoning behind this approach is as follows. The content of pending tax legislation begins to leak to the public prior to the scheduling of hearings and other official proclamations. Hence, adjustments of returns may begin to occur in the pre-announcement and pre-enactment phases of the event period. As investors come to anticipate specific changes in the tax code, they act on their expectations and returns begin to adjust before the event's official announcement. Return adjustments following the announcement and passage of TRA '86 were evaluated in terms of the significance of cumulative residuals over the period ED+1 to ED+60. The event windows considered in this article are listed in Table 1. The announcement of President Reagan's tax reform proposal and Chairman Rostenkowski's agreement to work with the Administration to draft a tax package are the main focuses of EW-1. Both Treasury I and II included modifications to the tax code that had important implications for insurers. …

An Analysis of Mesoscale Transport Phenomena during the Evening Transition Period near Sacramento, California

An analytical study of transport phenomena during the evening transition period in the vicinity of Sacramento, California is presented. The study is based on a network of double-theodolite wind stations, aircraft soundings and micrometeorological measurements made in the city. The transition period could be described in terms of three stability regimes: 1) moderately unstable (h/L = −4.19), 2) moderately stable (h/L = 1.06) and, later in the evening 3) very stable (h/L = 295). During the analysis period, the boundary layer depth first increased in the late afternoon unstable period, reaching a maximum depth of about 1 km, then dropped discontinuously to about 200 m in the early evening (moderately stable period). During the remainder of the evening, the boundary-layer depth increased steadily, extending to over 700 m after midnight. Comparison of aircraft soundings made up- and downwind of the city of Sacramento indicated that the city had the effect of increasing the boundary layer depth by an average of 165 m. During the stability transition, the temperature profile rapidly developed a strong, low level inversion, capping an extremely shallow (< = 100 m) unstable layer, presumably associated with the urban heat island. The most prominent feature of the soundings was the rapid development, during the period of moderate stability, of low-level transient jets in the wind field. The jet was associated with low-level maxima in the horizontal transport of moisture and sensible heat. The boundary layer water vapor budget was evaluated for the entire analysis period. All three stability regimes displayed approximate equilibrium. For each period, the depth-integrated balance was between vertical diffusion, as a source, and horizontal and vertical advection, as sinks. It is noteworthy that subsiding dry air was found to be important throughout the entire period.

Thunderstorm electrification: A case study

The paper presents interpretation of triple Doppler radar observations of a thunderstorm that occurred at the Kennedy Space Center, Florida. Precipitation particle motions inside the storm, as evaluated from the three radial velocity radar data sets, are presented in a selected vertical plane throughout the storm development. These data are interpreted and compared with observations of VHF radio emission sources and lightning charge centers derived from an earlier analysis (Krehbiel, 1981). The main feature of the particle motion field is the persistence, at nearly the same altitude throughout the entire period of analysis, of a “balance level” characterized by a zero value of the precipitation particle mean vertical velocity. Further analysis based on considerations of radar reflectivity and air velocity suggests the presence, at this altitude, of relatively large precipitation particles suspended in an updraft. The lightning negative charge centers appear to be less than 1 km above the particle balance level.

Energy Votes in the U.S. Senate, 1973-1980

The highly salient issue of energy policy presents an excellent opportunity to analyze roll-call voting in the U.S. Senate. In this study, both political party and state energy interests are shown to have importance in understanding senators' voting on energy matters in the 91st through 96th Congresses. Political party, together with region, however, is clearly the single most important variable in determining how senators vote during the entire period of analysis. A four-fold party/region variable proved to be the optimal explanatory variable of energy votes because it demonstrates the strategic position of the southern Democrats in the Senate from 1973-1980 on energy policy.

A Direct Recording Instrument for Size Analysis of Coarse Granular Material

I HAVE constructed a modified form of Emery's sedimentation tube1, by the help of which a direct picture of the size distribution of particles of coarse granular material can be obtained without recourse to calculations, computations and graphical representations. The new instrument consists mainly of a special form of long settling tube and a constant-speed revolving drum as shown in Fig. 1. The successive cumulative heights of the sedimentation column, over the entire period of analysis, are recorded on a photographic paper wrapped over the cylindrical drum. This photographic record at the successive stages of analysis presents a direct picture of the size-distribution character of the particles of the material analysed.

Space satellite may relav TV across ocean

SARAL/AltiKa, a joint Ka-band altimetry mission of the Centre National d’Etudes Spatiales (CNES) and Indian Space Research Organisation (ISRO) was successfully launched on February 25, 2013. The main purpose of this mission is to explore the ocean surface topography. As it is a Ka-band altimeter mission unlike other altimeters which were primarily in Ku-band, it is essential to calibrate and validate AltiKa data products before using the data for oceanographic applications. With this objective, two important geophysical parameters, Significant Wave Height (SWH) and Wind Speed (WS) from SARAL/AltiKa are inter-compared with those from 18 moored buoy stations in the North Indian Ocean (NIO) for a two year period from March 2013 to March 2015. SARAL/AltiKa GDR-T patch-2 version products are collocated with moored buoy observations with a collocation criteria of spatio-temporal window of 50 km radius about the buoy location and 30 min time for all the altimeter measurements. Following this, linear regression relations are developed and statistical analyses carried out to assess the performance of SARAL/AltiKa. The correlation between SARAL/AltiKa derived SWHs and those from moored buoys is 0.98 m with a bias of −0.02 m and Root Mean Square Error (RMSE) of 0.15 m at 95% confidence level. The WSs derived from SARAL/AltiKa Ka-band correlates reasonably well with buoy observations with a correlation coefficient of 0.91, bias of −0.28 m/s and RMSE of 1.13 m/s. The inter-comparison results are found to be interesting with a good agreement between SARAL/AltiKa and moored buoys observations of SWH and WS in the NIO where SWHs are less than ∼4 m and WS are less than ∼13 m/s during the entire analysis period.