Inter-seasonal and inter-annual variations of mean and eddy atmospheric energetics over India

Using daily upper air data from 1000 to 250 hPa of 20 stations during the period 1983-87 , the inter-sasonal and inter-annual variations of vertically intearated mean and eddy sensible and latent heat fluxes over India were examined. Vertically intearated meridional, sensible and latent fluxes (both mean and eddy fluxes) were generally southwards over the country except over northeastern parts. Large seasonal variation of mean sensible heat and latent heat flux values occur in association with the seasonal shifts of Hadley circulation. Maximum sensible heat fluxes were observed during pre-monsoon season over northern parts of India. Maximum latent heat fluxes were observed over central parts of India during monsoon season. Eddy fluxes were two order smaller than fluxes due to mean flow during all seasons. Maximum eddy fluxes occur in winter and are accomplished by large scale transient eddies. The eddy fluxes were practically negligible equatorwards of 15°N. Seasonal variations of fluxes over low latitudes were, however, different from the zonal pattern of annual cycle obtained by Oort (1971). There were significant differences in meridional mean and eddy flux values between 1983 (a good monsoon year) and 1987 (a bad monsoon year). During 1983 (1987) the sensible heat flux values due to transient eddies were equatorwards (polewards) during the premonsoon as well as monsoon seasons. Similarly during monsoon season of 1983 larger northward mean sensible and latent heat fluxes were observed. In addition there were significant differences in vertical structure of zonal sensible and latent heat fluxes between 1983 and 1987 also.

Preliminary results on the simulation of the 1999 Orissa super cyclone using a GCM with a new boundary layer code

& bl 'kks/k&Ik= esa ,u- ,e- vkbZ- Vh- ,y- vkbZ- ifj;kstuk ds ,d Hkkx ds :Ik esa fy[ks x, ,d u, ,- th- lh- ,e- dksM+ ¼uker% o"kkZ½ dk mi;ksx djrs gq, mM+hlk ds egkpØokr ds izfr:i.k ls izkIr fd, x, izkjfEHkd ifj.kkeksa dks izLrqr fd;k x;k gSA bZ- lh- ,e- MCY;w- ,Q- Vh-&106 dh vkjfEHkd voLFkkvksa dk mi;ksx djrs gq, 26 vDrwcj] 1999 dks 0000 ;w- Vh- lh- ij bl izfr:i.k dks vkjEHk fd;k x;k gSA gok ds >ksadsiu ds dkjd dks lfEefyr djrs gq, ekud eksuhu&vkscw[kkso ifjlhek Lrj dksM ls Vh&80 ds foHksnu ij o"kkZ dksM dk mi;ksx djrs gq, daVªksy ju fd;k x;k gSA 78 fd-eh- xzhM varjky ls 120 LisDVªy ekWMl esa mUur {kSfrt foHksnu vkSj eUn iouksa ij u, ifjlhek Lrj ds izkpyhdj.k ls dksM vla[; o`f);ksa dks n’kkZrk gS% izfr:i.k dks vkjEHk djus ds i'pkr~ vf/kdre =qfV esa 36 ?kaVksa dh vof/k esa 350 ls 234 fd-eh-] 48 ?kaVksa dh vof/k esa 310 ls 34 fd-eh- vkSj 96 ?kaVksa dh vof/k esa 410 ls 55 fd-eh- rd =qfV;ksa dh vf/kdre deh ikbZ xbZ gSA blesa ;g lq>ko fn;k x;k gS fd bl o`f) dk Js; i`"Bh; cyksa ds mUur vkdyu vkSj u, ifjlhek Lrj cy vk?kw.kZ ¼VkdZ½ dksM esa fufgr gSA blesa cy vk?kw.kZ ¼VkdZ½ dh Hkwfedk izeq[k ;ksxnku ds :Ik esa gh gS tksfd fo’ks"k :i ls pØokrksa dh i`"B Hkwfe ls lacaf/kr gSa tgk¡ ij iousa rqyukRed :i ls gYdh gksrh gSa fdarq ml {ks= esa fo|eku i`"Bh; cy rFkk bldh vk?kw.kZ Hkqtk ¼ewesaV vkeZ½ nksuksa vf/kd gksrh gSaA vk’p;Ztud :Ik ls mPprj i`"Bh; cy u, dksM }kjk iwokZuqekfur mPprj iouksa ls Hkh mRiUu gksrs gSaA blesa jkspd ckr ;g gS fd bldh i`"B Hkwfe pØokr ds ekxZ vkSj U;wure vonkc nksuksa esa u, ifjlhek Lrj ekM;wy ls mPprj foHksnu ds dkj.k gqbZ o`f) ls cgqr vf/kd lacaf/kr gSA pØokr iFk iwokZuqeku ij vU; Hkaoj ¶yDlksa ¼laos| m"ek] vknzZrk½ ds izHkko dk ewY;k¡du djus ds fy, vkSj vf/kd fo’ys"k.k djuk vko’;d gSA We present here preliminary results from the simulation of the Orissa super cyclone using a new AGCM code (named Varsha) written as part of a NMITLI project. The simulation is initialized at 0000 UTC, 26 October 1999, using ECMWF T-106 initial conditions. The control run is made using the Varsha code at a T-80 resolution with a standard Monin-Obukhov boundary layer code incorporating a gustiness factor. With the horizontal resolution improved to 120 spectral modes with a 78 km grid spacing, and a new boundary layer parameterization at low winds, the code shows substantial improvements: the maximum error is reduced from 350 to 234 km at 36 hr after initialization, 310 to 34 km at 48 hr, and 410 to 55 km at 96 hr. It is suggested that part of the explanation for this improvement lies in the improved estimation of surface forces and torque in the new boundary layer code. The role of torque is particularly interesting as the major contribution to it comes from the outer regions of the cyclone where the winds are relatively low but the area on which the surface force acts and its moment arm are both high. Intriguingly the higher surface forces arise also from the higher winds predicted by the new code. An interesting finding is that, on both track and minimum pressure, the improvement due to higher resolution is greater with the new boundary layer module. Further analysis is necessary to assess the effect of other eddy fluxes (sensible heat, moisture) on cyclone track prediction.

The relation between the zonal jets and ammonia anomalies in Jupiter

<div> <div>Juno's six‐channel MWR measurements might reveal information about the structure of the wind profile below the cloud level. These measurements are used to calculate the nadir brightness temperature (T<sub>b</sub>), a profile determined by temperature and by the opacity of the atmosphere. This opacity for the relevant frequencies of the MWR is determined mostly by ammonia abundance. The T<sub>b</sub> vary considerably between the different channels (indicating on different depths) and between latitudes. Here, we take the <!-- mathfontold --> T<sub>b</sub> as an indicator for ammonia concentration and examine the relation to the zonal jets. We find that different theoretical mechanisms can explain this relation at different latitudes. At the equatorial region, the superrotation is accompanied by vertical upwelling. This vertical advection, driven by a convergence of eddy fluxes directed perpendicular to the axis of rotation, is shown to explain the equatorial ammonia enrichment. At the mid-latitudes, assuming that the ammonia is enriched with depth, alternating Ferrel-like cells framed by opposite vertical velocities redistributes the ammonia, maximizing its meridional gradient where the jet peaks. This hypothesis is well apparent in the data, using both correlation analysis and theoretical arguments. We find that dynamical reasoning, suggesting on vertical velocities through the cloud-level zonal jets, can explain the latitudinal variations in <!-- mathfontold --> T<sub>b,</sub> under the assumption that they are caused by ammonia abundance anomalies.</div> </div>

Lagrangian eddy tracking reveals the Eratosthenes anticyclonicattractor in the eastern Levantine basin

<p>Statistics of anticyclone activity and trajectories in the southeastern Mediterranean sea over the period 2000-2018<br>is created using the DYNED atlas, which links the automated mesoscale eddy detection by the AMEDA algorithm with in<br>situ oceanographic observations. This easternmost region of the Mediterranean sea, delimited by the Levantine coast and<br>Cyprus, has a complex eddying activity, which has not yet been fully characterized. Using Lagrangian tracking<br>to investigate the eddy fluxes and interactions between different subregions in this area, we find that the southeastern Levantine<br>area is isolated, with no anticyclone exchanges with the western part of the basin. Moreover the anticyclonic structure above<br>the Eratosthenes seamount is identified as being an anticyclone attractor, differentiated from other anticyclones and staying<br>around this preferred position up to four years with successive mergings. Colocalized in situ profiles inside eddies provide<br>quantitative information on their subsurface structure and show that similar surface signatures correspond to very different<br>physical properties. Despite interannual variability, the so-called "Eratosthenes attractor" stores a larger amount of heat and<br>salt than neighboring anticyclones, in a deeper subsurface anomaly that usually extend down to 500 m. This suggests that this<br>attractor could concentrate heat and salt from this sub-basin, which will impact the properties of intermediate water masses<br>created there.</p>

Lagrangian eddy tracking reveals the Eratosthenes anticyclonic attractor in the eastern Levantine basin

Statistics of anticyclone activity and trajectories in the southeastern Mediterranean sea over the period 2000–2018 is created using the DYNED atlas, which links the automated mesoscale eddy detection by the AMEDA algorithm with in situ oceanographic observations. This easternmost region of the Mediterranean sea, delimited by the Levantine coast and Cyprus, has a complex eddying activity, which has not yet been fully characterized. In this paper we use Lagrangian tracking to investigate the eddy fluxes and interactions between different subregions in this area. We find that the southeastern Levantine area is isolated, with no anticyclone exchanges with the western part of the basin. Moreover the anticyclonic structure above the Eratosthenes seamount is identified as being an anticyclone attractor, differentiated from other anticyclones and staying around this preferred position up to four years with successive mergings. Colocalized in situ profiles inside eddies provide quantitative information on their subsurface structure and show that similar surface signatures correspond to very different physical properties. Despite interannual variability, the so-called Eratosthenes attractor stores a larger amount of heat and salt than neighbouring anticyclones, in a deeper subsurface anomaly that usually extend down to 500 m. This suggests that this attractor could concentrate heat and salt from this sub-basin, which will impact the properties of intermediate water masses created there.

A Geometric Perspective on the Modulation of Potential Energy Release by a Lateral Potential Vorticity Gradient

The release of available potential energy by growing baroclinic instability requires the slope of the eddy fluxes to be shallower than that of mean density surfaces, where the amount of energy released depends on both the flux angle and the distance of fluid parcel excursions against the background density gradient. The presence of a lateral potential vorticity (PV) gradient is known to affect the growth rate and energy release by baroclinic instability, but often makes the mathematics of formal linear stability analysis intractable. Here the effects of a lateral PV gradient on baroclinic growth are examined by considering its effects on the slope of the eddy fluxes. It is shown that the PV gradient systematically shifts the unstable modes toward higher wavenumbers and creates a cutoff to the instability at large scales, both of which steepen the eddy flux angle and limit the amount of energy released. This effect may contribute to the severe inhibition of baroclinic turbulence in systems dominated by barotropic jets, making them less likely to transition to turbulence-dominated flow regimes.

Metabolism of a subtidal rocky mussel reef in a high-temperate setting: pathways of organic C flow

Mytilid mussels form abundant, species-rich reefs on rocky substrates, but the role of this key habitat in carbon (C) cycling remains poorly understood. We performed a seasonal study on a 5 m deep photic Mytilus trossulus reef in the Central Baltic Sea to investigate pathways and rates of organic C flow. Reef gross primary production (GPP) and respiration (R) were estimated seasonally using underwater O2 eddy covariance on hourly and daily timescales. Photogrammetry and biotic sampling were used to quantify reef rugosity and mussel coverage, and to derive mussel filtration and biodeposition. Mussels were highly abundant, reaching ~50000 ind. m-2, and the reef structure increased the seabed surface area by 44%. GPPhourly was up to 20 mmol O2 m-2 h-1 and GPPdaily was up to 107 mmol O2 m-2 d-1, comparable to a nearby seagrass canopy. Hourly eddy fluxes responded linearly to light intensity and flow velocity, with higher velocities enhancing reef O2 uptake at night. Reef Rdaily exceeded GPPdaily on 12 of 13 measurement days, and Rannual (29 mol O2 m-2 yr-1) was 3-fold larger than GPPannual. The reef sustained a productive community of microbes and fauna whose activities accounted for ~50% of Rannual. Horizontal water advection promoted food supply to the reef and likely facilitated substantial lateral C export of mussel biodeposits. Our analyses suggest that a reduction in mussel reef extent due to ongoing environmental change will have major implications for the transport and transformation of C and nutrients within the coastal Baltic Sea.

The Generic Nature of the Tropospheric Response to Sudden Stratospheric Warmings

The tropospheric response to midwinter sudden stratospheric warmings (SSWs) is examined using an idealized model. SSW events are triggered by imposing high-latitude stratospheric heating perturbations of varying magnitude for only a few days, spun off from a free-running control integration (CTRL). The evolution of the thermally triggered SSWs is then compared with naturally occurring SSWs identified in CTRL. By applying a heating perturbation, with no modification to the momentum budget, it is possible to isolate the tropospheric response directly attributable to a change in the stratospheric polar vortex, independent of any planetary wave momentum torques involved in the initiation of an SSW. Zonal-wind anomalies associated with the thermally triggered SSWs first propagate downward to the high-latitude troposphere after ~2 weeks, before migrating equatorward and stalling at midlatitudes, where they straddle the near-surface jet. After ~3 weeks, the circulation and eddy fluxes associated with thermally triggered SSWs evolve very similarly to SSWs in CTRL, despite the lack of initial planetary wave driving. This suggests that at longer lags, the tropospheric response to SSWs is generic and it is found to be linearly governed by the strength of the lower-stratospheric warming, whereas at shorter lags, the initial formation of the SSW potentially plays a large role in the downward coupling. In agreement with previous studies, synoptic waves are found to play a key role in the persistent tropospheric jet shift at long lags. Synoptic waves appear to respond to the enhanced midlatitude baroclinicity associated with the tropospheric jet shift, and preferentially propagate poleward in an apparent positive feedback with changes in the high-latitude refractive index.